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Possibility of Power Tapping From
Composite ACDC Power Transmission
Lines
ABSTRACT
Large power (steam, hydro, nuclear) stations are usually located far from load
centers. The wheeling of this available electric energy from these remotely located
stations to load centers is achieved either with extra high voltage (EHV) ac or HVDC
transmission lines. These EHV ac/HVDC transmission lines often pass over relatively
small communities/rural areas that do not have access to a major power transmission
network. It is most desirable to find methods for connecting these communities to the
main transmission system to supply cheap and abundant electrical energy. However, the
HVDC transmission system does suffer a significant disadvantage compared to EHV ac
transmission, in regards to the tapping of power from a transmission system. Techno-
economical reasons prevent the tapping of a small amount of power from HVDC
transmission lines. This is considered a major drawback due to the fact that in many
instances, HVDC transmission lines pass over many rural communities that have little orno access to electricity.
A recently proposed concept of simultaneous acdc power transmission
enables the long extra high-voltage ac lines to be loaded close to their thermal limits. The
conductors are allowed to carry a certain amount of dc current superimposed on usual ac.
This paper presents the feasibility of small power tapping from composite acdc power
transmission lines which would pass over relatively small communities/rural areas having
no access to a major power transmission network. The proposed scheme is digitally
simulated with the help of a PSCAD/EMTDC software package. Simulation results
clearly indicate that the tapping of a small amount of ac power from the composite acdc
transmission line has a negligible impact on the normal functioning of the composite ac
dc power transmission system.
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CHAPTER 1
INTRODUCTION
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INTRODUCTION
1.1 INTRODUCTION ABOUT HVDC
High Voltage Direct Current (HVDC) transmission is widely recognized as
being advantageous for long-distance, bulk power delivery, asynchronous
interconnections and long submarine cable crossings. HVDC lines and cables are less
expensive and have lower losses than those for three-phase ac transmission.
Typical HVDC lines utilize a bipolar configuration with two independent poles and are
comparable to a double circuit ac line. Because of their controllability HVDC links offer
firm capacity without limitation due to network congestion or loop flow on parallel paths.
Higher power transfers are possible over longer distances with fewer lines with HVDC
transmission than with ac transmission. Higher power transfers are possible without
distance limitation on HVDC cables systems using fewer cables than with ac cable
systems due to their charging current.
HVDC systems became practical and commercially viable with the advent of high
voltage mercury-arc valves in the 1950s. Solid-state thyristor valves were introduced in
the late 1960s leading to simpler converter designs with lower operation and
maintenance expenses and improved availability. In the late 1990s a number of newer
converter technologies were introduced permitting wider use of HVDC transmission in
applications which might not otherwise be considered.
1.2 NEED FOR HVDC
High Voltage Direct Current (HVDC) transmission is widely recognized as beingadvantageous for long-distance, bulk power delivery, asynchronous interconnections and
long submarine cable crossings. HVDC lines and cables are less expensive and have
lower losses than those for three-phase ac transmission
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HVDC links offer firm capacity without limitation due to network congestion or
loop flow on parallel paths. Higher power transfers are possible over longer distances
with fewer lines with HVDC transmission than with ac transmission. Higher power
transfers are possible without distance limitation on HVDC cables systems using fewer
cables than with ac cable systems due to their charging current.
The main advantages of HVDC transmission systems are
1. Greater power per conductor
2. Simpler line construction
3. Ground return can be used hence each conductor can be operated as an independent
circuit.
4. No charging current
5. No skin effect
6. Cables can be worked at a higher voltage gradient
7. Line power factor is always unity; line does not require reactive compensation
8. Less corona loss.
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power upgrading has already been demonstrated by converting the EHV ac line into a
composite ac-dc transmission line without any alteration. The transmission angle can be
increased up to 80 in a composite ac-dc line without losing transient stability, which is
impossible in a pure EHV ac line.
From this composite acdc line, small power tapping is also possible
despite the presence of a dc component in it. This paper proposes a simple scheme of
small power tapping from the composite acdc power transmission line along its route. In
this study, the tapping stations are assumed to draw power up to 10% of the total power
transfer capability of the composite line. However, more power tapping is also possible
subject to the condition that it is always less than the ac power component.
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CHAPTER 2
INTRODUCTION
SIMULTANEOUS ACDC
POWER TRANSMISSION
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CHAPTER 2 INTRODUCTION
SIMULTANEOUS ACDC POWER TRANSMISSION
Fig. 1.1 depicts the basic scheme for simultaneous acdc power flow through
a double circuit ac transmission line. The dc power is obtained through line commutated12-pulse rectifier bridge used in conventional HVDC and injected to the neutral point of
the zigzag connected secondary of sending end transformer and is reconverted to ac again
by the conventional line commutated 12-pulse bridge inverter at the receiving end. The
inverter bridge is again connected to the neutral of zig-zag connected winding of the
receiving end transformer.
The double circuit ac transmission line carriers both three-phase ac and dc
power. Each conductor of each line carries one third of the total dc current along with ac
current. Resistance being equal in all the three phases of secondary winding of zigzag
transformer as well as the three conductors of the line, the dc current is equally divided
among all the three phases.
Fig. 1.1 Basic scheme for composite acdc transmission.
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Fig 1.2
2.1SYSTEM UNDER STUDY:
The network depicted in Fig.1.1 has been taken up for the feasibility of a small power tapfor remote communities from the composite acdc power transmission system. The
details of power tap substations are shown in Fig.1.2 A synchronous machine is
delivering power to an infinite bus via a double-circuit three-phase, 400-kV, 50-Hz, 450-
km ac transmission line. The minimum value of ac phase voltage and maximum value of
dc voltage with respect to ground of the converted composite acdc line, respectively, are
1/2 and times that of per phase voltage before conversion of the conventional pure
EHV ac line. The line considered is converted to a composite acdc transmission line
with an ac rated voltage of 220 kV and a dc voltage of 320 kV. In a composite acdc
transmission line, the dc component is obtained by converting a part of the ac through a
line-commutated 12-pulse rectifier bridge similar to that used in a conventional HVDC.
The dc current thus obtained is injected into the neutral point of the zig-zag-connected
secondary windings of sending end transformer. The injected current is distributed
equally among the three windings of the transformer. The same is reconverted to ac by
the conventional line commutated inverter at the receiving end. The inverter bridge is
connected to the neutral of zig-zag-connected winding of the receiving end transformer.
The transmission line is connected between the terminals of the zig-zag windings at both
ends. The double-circuit transmission line carries both three-phase ac as well as dc power
after conversion to a composite acdc line. The zig-zag connection of secondary
windings of the transformer is used at both ends to avoid saturation of the core due to the
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flow of the dc component of current. The replacement of a Y-connected transformer from
a conventional EHV ac line with a zig-zag transformer in composite acdc power
transmission is accomplished along with the reduction of ac voltage in such a way that
the insulation-level requirements remain unaltered. However, the neutral point of this
transformer needs insulation to withstand the dc voltage. Moreover, the zig-zag
transformer transfers only 25% of the total power by transformer action. To tap ac power
from the line, the transformer can be directly connected to the conductors of the line
without breaking them.
In this study of a composite ac-dc transmission line, the ac-line voltage component has
been selected as 220 kV. Each tapping station transformer (rated as 120 MVA, 220/66
kV, is connected to the local ac load via a circuit breaker (CB) as depicted in
Fig. 1(b). These CBs are provided for local protection, to clear the fault within the local
ac network. The nature of the local load considered here is that of a summer time
residential class with the following characteristics.
The three conductors of the second line provide return path for the dc current.
Zig-zag connected winding is used at both ends to avoid saturation of transformer due to
dc current. Two fluxes produced by the dc current Id /3 flowing through each of a winding
in each limb of the core of a zig-zag transformer are equal in magnitude and opposite in
direction. So the net dc flux at any instant of time becomes zero in each limb of the core.
Thus, the dc saturation of the core is avoided. A high value of reactor Xd is used to reduce
harmonics in dc current. In the absence of zero sequence and third harmonics or its
multiple harmonic voltages, under normal operating conditions, the ac current flow
through each transmission line will be restricted between the zigzag connected windings
and the three conductors of the transmission line. Even the presence of these components
of voltages may only be able to produce negligible current through the ground due to
high value of Xd. Assuming the usual constant current control of rectifier and constant
extinction angle control of inverter, the equivalent circuit of the scheme under normal
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steady-state operating condition is given in Fig. 2. The dotted lines in the figure show the
path of ac return current only. The second transmission line carries the return dc current,
and each conductor of the line carries Id/3 along with the ac current per phase and are the
maximum values of rectifier and inverter side dc voltages and are equal totimes converter ac input line-to-line voltage. R, L, and C are the line parameters per
phase of each line. , are commutating resistances, and, are firing and
extinction angles of rectifier and inverter, respectively. Neglecting the resistive drops in
the line conductors and transformer windings due to dc current, expressions for ac
voltage and current, and for active and reactive powers in terms of A, B, C, and D
parameters of each line may be written as
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Fig 2.1
Neglecting ac resistive drop in the line and transformer, the dc power Pdr and Pdi of each
rectifier and inverter may be expressed as
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The net current I in any conductor is offseted from zero. In case of a fault in the
transmission system, gate signals to all the SCRs are blocked and that to the bypass SCRs
are released to protect rectifier and inverter bridges. The current in any conductor is no
more offseted. Circuit breakers (CBs) are then tripped at both ends to isolate the faulty
line. CBs connected at the two ends of transmission line interrupt current at natural
current zeroes, and no special dc CB is required. Now, allowing the net current through
the conductor equal to its thermal limit (Ith)
Let Vph be per-phase rms voltage of original ac line. Let also V a be the per-phase voltage
of ac component of composite acdc line with dc voltage Vd superimposed on it. As
insulators remain unchanged, the peak voltage in both cases should be equal
Electric field produced by any conductor possesses a dc component superimpose on it a
sinusoidally varying ac component. However, the instantaneous electric field polarity
changes its sign twice in a cycle if is insured. Therefore, higher
creepage distance requirement for insulator discs used for HVDC lines are not required.
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Each conductor is to be insulated for, Vmax but the line-to-line voltage has no dc
component and. Therefore, conductor-to-conductor separation
distance of each line is determined only by rated ac voltage of the line. Allowing
maximum permissible voltage offset such that the composite voltage wave just toucheszero in each every cycle;
The total power transfer through the double circuit line before conversion is as follows:
Where X the transfer reactance per phase of the double is circuit line, and is the
power angle between the voltages at the two ends. To keep sufficient stability margin,
is generally kept low for long lines and seldom exceeds 30. With the increasing
length of line, the loadability of the line is decreased. An approximate value of may
be computed from the loadability curve by knowing the values of surge impedance
loading (SIL) and transfer reactance of the line
Where M is the multiplying factor, and its magnitude decreases with the length of line.
The value of M can be obtained from the loadability curve. The total power transfer
through the composite line
The power angle between the ac voltages at the two ends of the composite line may
be increased to a high value due to fast controllability of dc component of power. For a
constant value of total power, may be modulated by fast control of the current
controller of dc power converters. Approximate value of ac current per phase per circuit
of the double circuit line may be computed as
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The rectifier dc current order is adjusted online as
Preliminary qualitative analysis suggests that commonly used techniques in HVDC/AC
system may be adopted for the purpose of the design of protective scheme, filter, and
instrumentation network to be used with the composite line for simultaneous acdc power
flow. In case of a fault in the transmission system, gate signals to all the SCRs are
blocked and that to the bypass SCRs are released to protect rectifier and inverter bridges.
CBs are then tripped at both ends to isolate the complete system. A surge diverter
connected between the zig-zag neutral and the ground protects the converter bridge
against any over voltage.
2.2 SMALL POWER TAPPING STATION
REQUIREMENTS:The main requirements of a small power tapping stations are as follows.
The per unit cost of the tap must be strongly constrained (i.e., the fixed cost must be
kept as low as possible).
The tap must have a negligible impact on the reliability of the acdc system. This
implies that any fault in the tap must not be able to shutdown the whole system.
The tap controls should not interfere with the main system (i.e., the tap control system
has to be strictly local). Failure to achieve this leads to a complex control system
requirement and, thus, higher cost of hardware.
Small tap stations having a total rating less than 10% of the main terminal rating have
potential applications where small, remote communities or industries require economic
electric power.
The tapping stations considered in this study are of fairly small power rating, up to 10%
of the total transfer capacity of the composite ac-dc power transmission line. Short
interruption of the power supplies should be tolerable at the occurrence of temporary
earth faults on the main simultaneous acdc power transmission system. Further, any
fault occurring within tapping station and its local ac network is to be cleared by local
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CHAPTER 3
DESCRIPTION OF THE SYSTEM MODEL:
A synchronous machine is feeding power to infinite bus via a double circuit, three-phase,
400-KV, 50-Hz, 450-Km ac transmission line. The 2750-MVA (5 * 550), 240-KV
synchronous machine is dynamically modeled, a field coil on d-axis and a damper coil on
q-axis, by Parks equations with the frame of reference based in rotor. It is equipped with
an IEEE type
Fig 3.1
Fig 3.2
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AC4A excitation system of which block diagram is shown in Fig. 3. Transmission lines
are represented as the Bergeron model. It is based on a distributed LC parameter
travelling wave line model, with lumped resistance. It represents the L and C elements of
a PI section in a distributed manner (i.e., it does not use lumped parameters).
It is roughly equivalent to using an infinite number of PI sections, except that the
resistance is lumped (1/2 in the middle of the line, 1/4 at each end). Like PI sections,
the Bergeron model accurately represents the fundamental frequency only. It also
represents impedances at other frequencies, except that the losses do not change. This
model is suitable for studies where the fundamental frequency load flow is most
important. The converters on each end of dc link are modeled as line commutated two
six- pulse bridge (12-pulse), Their control system consist of constant current (CC) and
constant extinction angle (CEA) and voltage dependent current order limiters (VDCOL)
control. The converters are connected to ac buses via Y-Y and Y- converter transformers.
Each bridge is a compact power system computer-aided design (SIMULINK)
representation of a dc converter, which includes a built in six-pulse Graetz converter
bridge (can be inverter or rectifier), an internal phase locked oscillator (PLO), firing and
valve blocking controls, and firing angle /extinction angle measurements. It also
includes built in RC snubber circuits for each thyristor. The controls used in dc system
are those of CIGRE Benchmark , modified to suit at desired dc voltage. AC filters at each
end on ac sides of converter transformers are connected to filter out 11th and 13th
harmonics. These filters and shunt capacitor supply reactive power requirements of
converters.
A master current controller (MCC), shown in Fig. 3.2, is used to control the current order
for converters. It measures the conductor ac current, computes the permissible dc current,
and produces dc current order for inverters and rectifiers.
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CHAPTER 4
HVDC
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CHAPTER 4
4.1HVDC
Over long distances bulk power transfer can be carried out by a high
voltage direct current (HVDC) connection cheaper than by a long distance AC
transmission line. HVDC transmission can also be used where an AC transmission
scheme could not (e.g. through very long cables or across borders where the two AC
systems are not synchronized or operating at the same frequency). However, in order to
achieve these long distance transmission links, power convertor equipment is required,
which is a possible point of failure and any interruption in delivered power can be costly.
It is therefore of critical importance to design a HVDC scheme for a given availability.
The HVDC technology is a high power electronics technology used in
electric power systems. It is an efficient and flexible method to transmit large amounts of
electric power over long distances by overhead transmission lines or
underground/submarine cables. It can also be used to interconnect asynchronous power
systems
The fundamental process that occurs in an HVDC system is the conversion of
electrical current from AC to DC (rectifier) at the transmitting end and from DC to AC
(inverter) at the receiving end.
There are three ways of achieving conversion
1. Natural commutated converters.
2. Capacitor Commutated Converters.
3. Forced Commutated Converters.
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4.1.1Natural commutated converters (NCC):
NCC is most used in the HVDC systems as of today. The component
that enables this conversion process is the thyristor, which is a controllable
semiconductor that can carry very high currents (4000 A) and is able to block very high
voltages (up to 10 kV). By means of connecting the thyristors in series it is possible to
build up a thyristor valve, which is able to operate at very high voltages (several
hundred of kV).The thyristor valve is operated at net frequency (50 Hz or 60 Hz) and by
means of a control angle it is possible to change the DC voltage level of the bridge..
4.1.2Capacitor Commutated Converters (CCC):
An improvement in the thyristor-based Commutation, the CCC
concept is characterized by the use of commutation capacitors inserted in series between
the converter transformers and the thyristor valves. The commutation capacitors improve
the commutation failure performance of the converters when connected to weak
networks.
4.1.3Forced Commutated Converters(FCC).
This type of converters introduces a spectrum of advantages, e.g. feed
of passive networks (without generation), independent control of active and reactive
power, power quality. The valves of these converters are built up with semiconductors
with the ability not only toturn-on but also to turn-off. They are known as VSC (Voltage
Source Converters). a new type of HVDC has become available. It makes use of the more
advancedsemiconductor technology instead of thyristors for power conversion between
AC and DC. The semiconductors used are insulated gate bipolar transistors (IGBTs), and
theconverters are voltage source converters (VSCs) which operate with high switching
frequencies (1-2 kHz) utilizing pulse width modulation (PWM).
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4.2Configurations of HVDC
There are different types of HVDC systems which are
4.2.1Mono-polar HVDC system:
In the mono-polar configuration, two converters are connected by a single
pole line and a positive or a negative DC voltage is used. In Fig 4.1. There is only one
Insulated transmission conductor installed and the ground or sea provides the path for the
return current.
Fig 4.1
4.2.2Bipolar HVDC system:
This is the most commonly used configuration of HVDC transmission
systems. The bipolar configuration, shown in Fig. 4.2 Uses two insulated conductors as
Positive and negative poles. The two poles can be operated independently if both
Neutrals are grounded. The bipolar configuration increases the power transfer capacity.
Under normal operation, the currents flowing in both poles are identical and there is no
ground current. In case of failure of one pole power transmission can continue in the
other pole which increases the reliability. Most overhead line HVDC transmission
systems use the bipolar configuration.
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Fig 4.4
4.3 VOLTAGE-SOURCE CONVERTER:
A voltage-source converter is connected on its ac-voltage side to a
three-phase electric power network via a transformer and on its dc-voltage side to
capacitor equipment. The transformer has on its secondary side a first, a second, and a
third phase winding, each one with a first and a second winding terminal. Resistor
equipment is arranged at the transformer for limiting the current through the converter
when connecting the transformer to the power network. The resistor equipment includes a
first resistor, connected to the first winding terminal of the second phase winding, and
switching equipment is adapted, in an initial position, to block current through the phase
windings, in a transition position to form a current path which includes at least the first
and the second phase windings and, in series therewith, the first resistor, which current
path, when the converter is connected to the transformer, closes through the converter
and the capacitor equipment, and, in an operating position, to interconnect all the first
winding terminals for forming the common neutral point.
In VSC HVDC, Pulse Width Modulation (PWM) is used for generation of
the fundamental voltage. Using PWM, the magnitude and phase of the voltage can be
controlled freely and almost instantaneously within certain limits. This allows
independent and very fast control of active and reactive power flows. PWM VSC is
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therefore a close to ideal component in the transmission network. From a system point of
view, it acts as a zero inertia motor or generator that can control active and reactive
power almost instantaneously. Furthermore, it does not contribute to the short-circuit
power, as the AC current can be controlled.
4.4Voltage Source Converter based on IGBT technology
The modular low voltage power electronic platform is called
PowerPak. It is a power electronics building block (PEBB) with three integrated
Insulated Gate Bipolar Transistor (IGBT) modules. Each IGBT module consists of six
switches forming three phase legs. Various configurations are possible. For example
three individual three-phase bridges on one PEBB, one three phase bridge plus
chopper(s) etc. The PowerPak is easily adaptable for different applications.
The IGBT modules used are one Power Pak as it is used for the SVR. It
consists of one three-phase bridge (the three terminals at the right hand side), which
provides the input to the DC link (one IGBT module is used for it) and one output in form
of one single phase H-bridge (the two terminals to the left) acting as the booster
converter. For the latter two IGBT modules are used with three paralleled phase legs per
output terminal. By paralleling such PEBBs adaptation to various ratings is possible.
4.5GTO/IGBT (Thyristor based HVDC):
Normal thyristors (silicon controlled rectifiers) are not fully controllable
switches (a "fully controllable switch" can be turned on and off at will.) Thyristors can
only be turned ON and cannot be turned OFF. Thyristors are switched ON by a gate
signal, but even after the gate signal is de-asserted (removed), the thyristor remains in the
ON-state until any turn-off condition occurs (which can be the application of a reverse
voltage to the terminals, or when the current flowing through (forward current) falls
below a certain threshold value known as the holding current.) Thus, a thyristor behaves
like a normal semiconductor diode after it is turned on or "fired".
The GTO can be turned-on by a gate signal, and can also be turned-off
by a gate signal of negative polarity.
Turn on is accomplished by a positive current pulse between the gate and cathode
terminals. As the gate-cathode behaves like PN junction, there will be some relatively
small voltage between the terminals. The turn on phenomenon in GTO is however, not as
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reliable as an SCR (thyristor) and small positive gate current must be maintained even
after turn on to improve relieabilty.
Turn off is accomplished by a negative voltage pulse between the gate and cathode
terminals. Some of the forward current (about one third to one fifth) is "stolen" and used
to induce a cathode-gate voltage which in turn induces the forward current to fall and the
GTO will switch off (transitioning to the 'blocking' state.)
GTO thyristors suffer from long switch off times, whereby after the
forward current falls, there is a long tail time where residual current continues to flow
until all remaining charge from the device is taken away. This restricts the maximum
switching frequency to approx 1 kHz.
It may however be noted that the turn off time of a comparable SCR is
ten times that of a GTO.Thus switching frequency of GTO is much better than SCR.
Gate turn-off (GTO) thyristors are able to not only turn on the main
current but also turn it off, provided with a gate drive circuit. Unlike conventional
thyristors, they have no commutation circuit, downsizing application systems while
improving efficiency. They are the most suitable for high-current, high speed switching
applications, such as inverters and chopper circuits.
Bipolar devices made with SiC offer 20-50X lower switching losses as
compared to conventional semiconductors. A rough estimate of the switching power
losses as a function of switching frequency is shown in Figure 4. Another very significant
property of SiC bipolar devices is their lower differential on-state voltage drop than
similarly rated Si bipolar device, even with order of magnitude smaller carrier lifetimes in
the drift region.
This property allows high voltage (>20 kV) to be far more reliable and
thermally stable as compared to those made with Silicon. The switching losses and the
temperature stability of bipolar power devices depends on the physics of operation of the
device. The two major categories of bipolar power devices are: (a) single injecting
junction devices (for example BJT and IGBT); and (b) double injecting junction devices
(like Thyristor-based GTO/MTO/JCT/FCT and PIN diodes). In a power BJT, most of the
minority carrier charge resides in the low doped collector layer, and hence its operation
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has been approximated as an IGBT. The limited gain of a BJT will make the following
analysis less relevant for lower voltage devices.
Silicon carbide has been projected to have tremendous potential for high voltage
solid-state power devices with very high voltage and current ratings because of its
electrical and physical properties. The rapid development of the technology for producing
high quality single crystal SiC wafers and thin films presents the opportunity to fabricate
solid- state devices with power-temperature capability far greater than devices currently
available. This capability is ideally suited to the applications of power conditioning in
new more- electric or all-electric military and commercial vehicles.
These applications require switches and amplifiers capable of large currents with
relatively low voltage drops. One of the most pervasive power devices in silicon is the
Insulated Gate Bipolar Transistor (IGBT). However, these devices are limited in their
operating temperature and their achievable power ratings compared to that possible with
SiC. Because of the nearly ideal combination of characteristics of these devices, we
propose to demonstrate the first 4H-SiC Insulated Gate Bipolar Transistor in this Phase I
effort. Both n-channel and p-channel SiC IGBT devices will be investigated. The targeted
current and voltage rating for the Phase I IGBT will be a >200 Volt, 200 mA device, that
can operate at 350 C.
4.6 12-pulse converters:The basic design for practically all HVDC converters is the 12-pulse double
bridge converter which is shown in Figure below. The converter consists of two 6-pulse
bridge converters connected in series on the DC side. One of them is connected to the AC
side by a YY-transformer, the other by a YD transformer. The AC currents from each 6-
pulse converter will then be phase shifted 30. This will reduce the harmonic content in
the total current drawn from the grid, and leave only the characteristic harmonics of order
12 m1, m=1,2,3..., or the 11th, 13th, 23th, 25th etc. harmonic. The non-characteristic
harmonics will still be present, but considerably reduced. Thus the need for filtering is
substantially reduced, compared to 6-pulse converters. The 12-pulse converter is usually
built up of 12 thyristor valves. Each valve consists of the necessary number of thyristors
in series to withstand the required blocking voltage with sufficient margin. Normally
there is only one string of thyristors in each valve, no parallel connection. Four valves are
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built together in series to form a quadruple valve and three quadruple valves, together
with converter transformer, controls and protection
Figure:4.5 -12-pulse converter.
Fig 4.6 Main elements of a HVDC converter station with one bipole consisting
of two 12-pulse converter unit.
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equipment, constitute a converter. The converter transformers are usually three winding
transformers with thewindings in Yy d N-connection. There can be one three-phase or
three single phase transformers, according to local circumstances. In order to optimize the
relationship between AC- and DC voltage the converter transformers are equipped with
tap changers.
4.7 HVDC converter stations:
An HVDC converter station is normally built up of one or two 12-pulse converters
as described above, depending on the system being mono- or bipolar. In some cases each
pole of a bipolar system consists of two converters in series to increase the voltage and
power rating of the transmission. It is not common to connect converters directly in
parallel in one pole. The poles are normally as independent as possible to improve the
reliability of the system, and each pole is equipped with a DC reactor and DC filters.
Additionally the converter station consists of some jointly used equipment.
This can be the connection to the earth electrode, which normally is situated some
distance away from the converter station area, AC filters and equipment for supply of the
necessary reactive power.
Fig 4.7 Mono-polar HVDC transmission Voltage in station B according to reversed
polarity convention.
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CHAPTER 5
BASIC CONTROL PRINCIPLES
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CHAPTER 5
BASIC CONTROL PRINCIPLES
5.1Control System Model:
The control model mainly consists of measurements and generation of firing signals for
both the rectifier and inverter. The PLO is used to build the firing signals. The output
signal of the PLO is a ramp, synchronized to the phase-A commutating bus line-to-
ground voltage, which is used to generate the firing signal for Valve 1. The ramps for
other valves are generated by adding 60 to the Valve 1 ramp. As a result, an equidistant
pulse is realized. The actual firing time is calculated by comparing the order to the value
of the ramp and using interpolation technique. At the same time, if the valve is pulsed but
its voltage is still less than the forward voltage drop, this model has logic to delay firing
until the voltage is exactly equal to the forward voltage drop. The firing pulse is
maintained across each valve for 120.
The and measurement circuits use zero-crossing information from commutating bus
voltages and valve switching times and then convert this time difference to an angle
(using measured PLO frequency). Firing angle (in seconds) is the time when valve turns
on minus the zero crossing time for valve.
Extinction angle (in seconds) for valve is the time at which the commutation bus voltage
for valve crosses zero (negative to positive) minus the time valve turns off.
Following are the controllers used in the control schemes:
Extinction Angle Controller;
DC Current Controller;
Voltage Dependent Current Limiter (VDCOL).
5.1.1 Rectifier Control: The rectifier control system uses Constant Current Control
(CCC) technique. The reference for current limit is obtained from the inverter side.
This is done to ensure the protection of the converter in situations when inverter side does
not have sufficient dc voltage support (due to a fault) or does not have sufficient load
requirement (load rejection). The reference current used in rectifier control depends on
the dc voltage available at the inverter side. Dc current on the rectifier side is measured
using proper transducers and passed through necessary filters before they are compared to
produce the error signal. The error signal is then passed through a PI controller, which
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produces the necessary firing angle order. The firing circuit uses this information to
generate the equidistant pulses for the valves using the technique described earlier.
5.1.2 Inverter Control:The Extinction Angle Control or control and current control
have been implemented on the inverter side. The CCC with Voltage Dependent Current
Order Limiter (VDCOL) has been used here through PI controllers. The reference limit
for the current control is obtained through a comparison of the external reference
(selected by the operator or load requirement) and VDCOL (implemented through lookup
table) output. The measured current is then subtracted from the reference limit to produce
an error signal that is sent to the PI controller to produce the required angle order.
The control uses another PI controller to produce gamma angle order for the inverter.
The two angle orders are compared, and the minimum of the two is used to calculate the
firing instant.
5.2 Control System Model:
The control blocks available in SIMULINK have been used to emulate the control
algorithm described above Section, and enough care has been taken. Some control
parameters required conversion to their proper values due to differences in units. The
rectifier side uses current control with a reference obtained from the inverter VDCOL
output (implemented through a lookup table), and the inverter control has both current
control and control operating in parallel, and the lower output of the two is used to
generate the firing pulses. The angle is not provided directly from the converter valve
data. It needed to be implemented through measurements taken from valve data. The
control block diagrams are shown in following figures.
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fig 5.1
fig 5.2
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Fig 5.3
5.3DC transmission controlThe current flowing in the DC transmission line shown in Figure below is determined by
the DC voltage difference between station A and station B. Using the notation shown in
the figure, where rdrepresents the total resistance of the line, we get for the DC current
and the power transmitted into station B is
2In rectifier operation the firing angle should not be decreased below a certain
minimum value min, normally 3-5 in order to make sure that there really is a positive
voltage across the valve at the firing instant. In inverter operation the extinction angle
should never decrease below a certain minimum value min, normally 17-19 otherwise
the risk of commutation failures becomes too high. On the other hand, both and
should be as low as possible to keep the necessary nominal rating of the equipment to a
minimum. Low values of and also decrease the consumption of reactive power and
the harmonic distortion in the AC networks.
To achieve this, most HVDC systems are controlled to maintain = min in normal
operation. The DC voltage level is controlled by the transformer tap changer in inverter
station B. The DC current is controlled by varying the DC voltage in rectifier station A,
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The current/voltage characteristics expressed in above are shown for normal values ofid
and dxN. In order to create a characteristic diagram for the complete transmission, it is
usual to define positive voltage in inverter operation in the opposite direction compared
to rectifier operation.
It is clear that to operate both converters on a constant firing/extinction angle principle is
like leaving them without control. This will not give a stable point of operation, as both
characteristics have approximately the same slope. Small differences appear due to
variations in transformer data and voltage drop along the line. To gain the best possible
control the characteristics should cross at as close to a right angle as possible. This means
that one of the characteristics should preferably be constant current. This can only be
achieved by a current controller.
If the current/voltage diagram of the rectifier is combined with a constant current
controller characteristic we get the steady state diagram in Figure below for converter
station A. A similar diagram can be drawn for converter station B. If we apply the
reversed polarity convention for the inverter and combine the diagrams for station A and
station B we get the diagram in Figure below In normal operation, the rectifier will be
operating in current control mode with the firing angle
Fig 5.4 Steady state ud/id diagram for converter station A Steady state ud/id diagram
for converter station A.&B
The inverter has a slightly lower current command than the rectifier and tries to decrease
the current by increasing the counter voltage, but cannot decrease beyond min. Thus
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we get the operating point A. We assume that the characteristic for station B is referred to
station A that is it is corrected for the voltage drop along the transmission line. This
voltage drop is in the magnitude of 1-5 % of the rated DC voltage. If the AC voltage at
the rectifier station drops, due to some external disturbance, the voltage difference is
reduced and the DC current starts to sink. The current controller in the rectifier station
starts to reduce the firing angle , but soon meets the limit min, so the current cannot be
upheld. When the current sinks below the current command of the inverter, the inverter
control reduces the counter voltage to keep the current at the inverter current command,
until a new stable operating point B is reached. If the current command at station A is
decreased below that of station B, station A will see a current that is to high and start to
increase the firing angle , to reduce the voltage. Station B will see a diminishing current
and try to keep it up by increasing the extinction angle to reduce the counter voltage.
Finally station A meets the min limit and cannot reduce the voltage any further and the
new operating point will be at point C. Here the voltage has been reversed to negative
while the current is still positive, that is the power flow has been reversed. Station A is
operating as inverter and station B as rectifier. The difference between the current
commands of the rectifier and the inverter is called the current margin. It is possible to
change the power flow in the transmission simply by changing the sign of the current
margin, but in practice it is desirable to do this in more controllable ways. Therefore the
inverter is normally equipped with a min limitation in the range of 95-105. To avoid
current fluctuations between operating points A and B at small voltage variations the
corner of the inverter characteristic is often cut off. Finally, it is not desirable to operate
the transmission with high currents at low voltages, and most HVDC controls are
equipped with voltage dependent current command limitation.
CHAPTER 6
Master control system:
The controls described above are basic and fairly standardized and similar for all HVDC
converter stations. The master control, however, is usually system specific and
individually designed. Depending on the requirements of the transmission, the control
can be designed for constant current or constant power transmitted, or it can be designed
to help stabilizing the frequency in one of the AC networks by varying the amount of
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active power transmitted. The control systems are normally identical in both converter
systems in a transmission, but the master control is only active in the station selected to
act as the master station, which controls the current command. The calculated current
command is transmitted by a communication system to the slave converter station, where
the pre-designed current margin is added if the slave is to act as rectifier, subtracted if it
is to act as inverter. In order to synchronize the two converters and assure that they
operate with same current command (apart from the current margin), a
telecommunications channel is required.
Should the telecommunications system fail for any reason, the current commands to both
converters are frozen, thus allowing the transmission to stay in operation. Special fail-
safe techniques are applied to ensure that the telecommunications system is fault-free.
The requirements for the telecommunications system are especially high if the
transmission is required to have a fast control of the transmitted power, and the time
delay in processing and transmitting these signals will influence the dynamics of the total
control system.
CHAPTER 7
7.1Comparison of Different HVAC-HVDC
In order to examine the behavior of the losses in combined transmission and not in order
to provide the best economical solutions for real case projects. Thus, most of the
configurations are overrated, increasing the initial investment cost and consequently the
energy transmission cost. The small number of different configurations analyzed provides
a limited set of results, from which specific conclusions can be drawn regarding the
energy transmission cost. Nevertheless, the same approach, as for the individual
HVACHVDC systems, is followed in order to evaluate the energy availability and the
energy transmission cost.
7.2 Presentation of Selected Configurations and Calculation of theEnergy Transmission Cost
For the combined HVAC-HVDC transmission systems only 500 MW and 1000 MW
windfarm were considered.
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The choices for the transmission distance were limited to 50, 100 and 200 km. The three
following, general combinations were compared:
1. HVAC + HVDC VSC
2. HVAC + HVDC LCC
3. HVDC LCC + HVDC VSC
The specific configurations for each solution, based on the transmission distance and the
size of the wind farm, are presented in Tables.
500MW Wind Farm, 50Km Transmission DistanceHVAC+HVDC VSC HVAC+HVDC LCC HVDC LCC+HVDC
Case 1 Case 2 Case 1 Case2 Case 1 Case 2
Rated Power 280MW(
400KV )AC+
230MV
VSC
150MW(2
30KV)Ac+
350MW
VSC
200MW(2
20KV)AC+
300MW
LCC
60MW(220K
v) AC+400MW
LCC
300MW
LCC+220MW
VSC
250MW
LCC+350MW
VSC
CableNumbers
1 (AC)+
2 VSC
1 (AC)+
2 VSC
1 (AC)+
1 LCC
1 (AC)+
1 LCC
1 (LCC)+
2 VSC
1 (LCC)+
2 VSC
500MW Wind Farm, 100Km Transmission DistanceHVAC+HVDC VSC HVAC+HVDC LCC HVDC LCC+HVDC
Case 1 Case 2 Case 1 Case 2 Case 1 Case 2
Rated Power 280MW
(400KV)
AC +230MV
VSC
150MW
(230KV)
AC +350MW
VSC
370MW
(400KV)A
C +130MW
LCC
250MW
(400KV)AC
+ 250MWLCC
300MW
LCC +
220MWVSC
250MW
LCC +
350MWVSC
Cable
Numbers
1 (AC)+
2 VSC
1 (AC)+
2 VSC
1 (AC)+
1 LCC
1 (AC)+
1 LCC
1 (LCC)+
2 VSC
1 (LCC)+
2 VSC
500MW Wind Farm, 200Km Transmission Distance
HVAC+HVDC VSC HVAC+HVDC LCC HVDC LCC+HVDC
Case 1 Case 2 Case 1 Case 2 Case 1 Case 2
Rated Power 280MW
(220KV)Ac +
220MV
VSC
150MW
(230KV)AC +
350MW
VSC
370MW
(400KV)AC +
130MW
LCC
250MW
(400KV)AC+ 250MW
LCC
300MW
LCC +220MW
VSC
250MW
LCC +350Mw
VSC
Cable
Numbers
1 (AC)+
2 VSC
1 (AC)+
2 VSC
1 (AC)+
1 LCC
1 (AC)+
1 LCC
1 (LCC)+
2 VSC
1 (LCC)+
2 VSC
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Table 1:Configurations for the study of combined transmission systems. Windfarm
rated at 500 MW
1000MW Wind Farm, 50Km Transmission DistanceHVAC+HVDC VSC HVAC+HVDC LCC HVDC LCC+HVDC
Case 1 Case2 Case 1 Case 2
Rated Power 200MW(220Kv)AC+ (2x350+220)MW
VSC
200MW(400KV)
AC+(600+2
50)MW
LCC
330MW(400KV)AC
+(600+130)
MW LCC
600MWLCC+
(350+220)
MWVSC
250MWLCC+
(2x350+
220) VSC
Cable
Numbers
1 (Ac)+ 4 (VSC) 1 (AC)+
2 LCC
1 (AC)+
2 LCC
1 (LCC)+
24 VSC
1 (LCC)+
6 VSC
1000MW Wind Farm, 100Km Transmission DistanceHVAC+HVDC VSC HVAC+HVDC LCC HVDC LCC+HVDC
Case 1 Case 2 Case 1 Case 2
Rated Power 500MW(400KV)
AC+ (350+220)MW VSC
800MW
(400KV)AC
+ 250MW
LCC
900MW
(400KV)AC+ 130MW
LCC
600MW
LCC+(350+220)
MW
VSC
250MW
LCC+(2x350+220) VSC
Cable
Numbers
1 (AC)+ 4(VSC) 2 (AC)+
1 LCC
2 (AC)+
1 LCC
1 (LCC)+
4 VSC
1 (LCC)+
6 VSC1000MW Wind Farm, 200Km Transmission Distance
HVAC+HVDC VSC HVAC+HVDC LCC HVDC LCC+HVDC
Case 1 Case 2 Case 1 Case 2
Rated Power 500MW(220KV)A
C+ (350+220)MWVSC
800MW
(220KV)AC +
250MW
LCC
9000MW
(220KV)AC+ 130MW
LCC
600MW
LCC+(350+22
0)MW
VSC
250MW LCC
+(2x350+220)
VSC
CableNumbers
2(AC)+ 24(VSC) 3 (AC)+1 LCC
4(AC)+1 LCC
1 (LCC)+4 VSC
1 (LCC)+6 VSC
Tab 2 Configurations for the study of combined transmission systems. Wind farm
rated at 1000
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Only the rated power of each transmission technology changes every time while the
distance to shore and the condition of the onshore grid remain the same.
1. The HVAC system has a voltage level of 220 kV and it connected to a weak
grid 50 km from the offshore substation.
2. The HVDC VSC system is connected to a grid of medium strength at a distance
of 100 km from the offshore substation.
3. The HVDC LCC system is connected to a strong grid 200 km from the offshore
substation. The average losses for the cases described above were calculated by
Barberis table-1 and Todorovic table-2. The losses and the results concerning
the energy unavailability and the energy transmission cost are presented in
Table -3.
1000 MW Windfarm with Multiple Connection Points to Shore
Besides the combinations of the transmission technologies presented above, three cases
of transmission solutions from a 1000 MW windfarm are analyzed. In these cases the
windfarm is connected to three different onshore grids, utilizing all three transmission
technologies studied so far.
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Tab 3
Average power losses, energy unavailability and energy transmission cost for
transmission solutions from a 1000 MW windfarm with multiple connection points
to shore.
CHAPTER 8
Simulink circuit:
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Fig 8.1
Zig zag transformer
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Fig 8.2
Controlling circuit
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fig 8.3
fig8.4
CHAPTER 9
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Blocks functionalities :
9.1Three-Phase Source:
The Three-Phase Source block implements a balanced three-phase voltage source with
internal R-L impedance. The three voltage sources are connected in Y with a neutral
connection that can be internally grounded or made accessible. You can specify the
source internal resistance and inductance either directly by entering R and L values or
indirectly by specifying the source inductive short-circuit level and X/R ratio.
9.2Three-Phase Parallel RLC Branch:
The Three-Phase Parallel RLC Branch block implements three balanced branches
consisting each of a resistor, an inductor, a capacitor, or a parallel combination of these.
To eliminate either the resistance, inductance, or capacitance of each branch, the R, L,and C values must be set respectively to infinity (inf), infinity (inf), and 0. Only existing
elements are displayed in the block icon. Negative values are allowed for resistance,
inductance, and capacitance
9.3Three-Phase Transformer (Three Windings):
This block implements a three-phase transformer by using three single-phase
transformers with three windings. You can simulate the saturable core or not simply by
setting the appropriate check box in the parameter menu of the block. See the Linear
Transformer and Saturable Transformer block sections for a detailed description of the
electrical model of a single-phase transformer.
The three windings of the transformer can be connected in the following manner: Y Y
with accessible neutral (for windings 1 and 3 only) Grounded Y Delta (D1), delta lagging
Y by 30 degrees Delta (D11), delta leading Y by 30 degrees.
9.4Universal Bridge:
The Universal Bridge block implements a universal three-phase power converter that
consists of up to six power switches connected in a bridge configuration. The types of
power switch and converter configuration are selectable from the dialog box.
The Universal Bridge block allows simulation of converters using both naturally
commutated (and line-commutated) power electronic devices (diodes or thyristors) and
forced-commutated devices (GTO, IGBT, and MOSFET).
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The Universal Bridge block is the basic block for building two-level voltage-sourced
converters (VSC).
9.5Connection Port:
The Connection Port block, placed inside a subsystem composed of SimPowerSystems
blocks, creates a Physical Modeling open round connector port on the boundary of the
subsystem. Once connected to a connection line, the port becomes solid. Once you begin
the simulation, the solid port becomes an electrical terminal port, an open square.
You connect individual SimPowerSystems blocks and subsystems made of sim Power
Systems blocks to one another with Sim Power Systems connection lines, instead of
normal Simulink signal lines. These are anchored at the open, round connector ports.
Subsystems constructed of SimPowerSystems blocks automatically have such open round
connector ports. You can add additional connector ports by adding Connection Port
blocks to your subsystem
9.6Breaker
The Breaker block implements a circuit breaker where the opening and closing times can
be controlled either from an external Simulink signal (external control mode), or from an
internal control timer (internal control mode).
The arc extinction process is simulated by opening the breaker device when the current
passes through 0 (first current zero crossing following the transition of the Simulink
control input from 1 to 0).
When the breaker is closed it behaves as a resistive circuit. It is represented by a
resistance Ron. The Ron value can be set as small as necessary in order to be negligible
compared with external components (typical value is 10 m). When the breaker is open it
has an infinite resistance.
If the Breaker block is set in external control mode, a Simulink input appears on the
block icon. The control signal connected to the Simulink input must be either 0 or 1: 0 to
open the breaker, 1 to close it. If the Breaker block is set in internal control mode, the
switching times are specified in the dialog box of the block.
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If the breaker initial state is set to 1 (closed), SimPowerSystems automatically initializes
all the states of the linear circuit and the Breaker block initial current so that the
simulation starts in steady state.
A series Rs-Cs snubber circuit is included in the model. It can be connected to the circuit
breaker. If the Breaker block happens to be in series with an inductive circuit, an open
circuit or a current source, you must use a snubber.
9.7 Distributed Parameter Line:
Implement an N-phase distributed parameter transmission line model with lumped losses.
The Distributed Parameter Line block implements an N-phase distributed parameter line
model with lumped losses. The model is based on the Bergeron's traveling wave method
used by the Electromagnetic Transient Program (EMTP).In this model, the lossless
distributed LC line is characterized by two values (for a single-phase line) For multiphase
line models, modal transformation is used to convert line quantities from phase values
(line currents and voltages) into modal values independent of each other. The previous
calculations are made in the modal domain before being converted back to phase values.
In comparison to the PI section line model, the distributed line represents wave
propagation phenomena and line end reflections with much better accuracy.
CHAPTER 10
Description of the Control and Protection Systems:
The control systems of the rectifier and of the inverter use the same Discrete HVDC
Controller block from the Discrete Control Blocks library of the SimPowerSystems
Extras library. The block can operate in either rectifier or inverter mode. At the inverter,
the Gamma Measurement block is used and it is found in the same library. The Master
Control system generates the current reference for both converters and initiates the
starting and stopping of the DC power transmission.
The protection systems can be switched on and off. At the rectifier, the DC fault
protection detects a fault on the line and takes the necessary action to clear the fault. The
Low AC Voltage Detection subsystem at the rectifier and inverter serves to discriminate
between an AC fault and a DC fault. At the inverter, the Commutation Failure Prevention
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Control subsystem [2] mitigates commutation failures due to AC voltage dips. A more
detailed description is given in each of these protection blocks.
10.1HVDC Controller Block Inputs and Outputs
Inputs 1and 2 are the DC line voltage (VdL) and current (Id). Note that the measured DC
currents (Id_R and Id_I in A) and DC voltages (VdL_R and VdL_I in V) are scaled to
p.u. (1 p.u. current = 2 kA; 1 p.u. voltage = 500 kV) before they are used in the
controllers. The VdL and Id inputs are filtered before being processed by the regulators.
A first-order filter is used on the Id input and a second-order filter is used on the VdL
input.
Inputs 3 and 4 (Id_ref and Vd_ref) are the Vd and Id reference values in p.u.
Input 5 (Block) accepts a logical signal (0 or 1) used to block the converter when Block =
1.
Input 6 (Forced-alpha) is also a logical signal that can be used for protection purposes. If
this signal is high (1), the firing angle is forced at the value defined in the block dialog
box.
Input 7 (gamma_meas) is the measured minimum extinction angle of the converter 12
valves. It is obtained by combining the outputs of two 6-pulse Gamma Measurement
blocks. Input 8 (gamma_ref) is the extinction angle reference in degrees. To minimize the
reactive power absorption, the reference is set to a minimum acceptable angle (e.g., 18deg).
Finally, input 9 (D_alpha) is a value that is subtracted from the delay angle maximum
limit to increase the commutation margin during transients.
The first output (alpha_ord) is the firing delay angle in degrees ordered by the regulator.
The second output (Id_ref_lim) is the actual reference current value (value of Id_ref
limited by the VDCOL function as explained below). The third output (Mode) is an
indication of the actual state of the converter control mode. The state is given by a
number (from 0 to 6) as follows:
0 Blocked pulses
1. Current control
2. Voltage control
3. Alpha minimum limitations
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CHAPTER 11
RESULTS:
Fig 12.1
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Fig 12.2
Fig 12.3
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Fig 12.4
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Fig 12.5
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Fig 12.6
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Fig 12.7
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Fig 12.8
CHAPTER 12
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CONCLUSION:
The feasibility of tapping a small amount of power to feed remotely located communities
in the same simple way as tapping in the case of an EHV ac line is demonstrated for the
composite acdc transmission system. It is also economical compared to complicated
methods of tapping from the HVDC line. The results clearly demonstrate that the tapping
of a small amount of ac component of power from the composite acdc transmission line
has a negligible impact on the dc power transfer.
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APPENDIX
SOFTWARE
MATLAB - SIMULINK
What is MATLAB?
MATLAB (Matrix Laboratory) is a tool for numerical
computation and visualization. The basic data element is a matrix, so if you need a
program that manipulates array-based data it is generally fast to write and run in
MATLAB (unless you have very large arrays or lots of computations, in which case
youre better off using C or Fortran).
MATLAB is a numerical computing environment andfourth-
generation programming language. Developed by Math Works, MATLAB allowsmatrix
manipulations, plotting offunctions and data, implementation ofalgorithms, creation of
user interfaces, and interfacing with programs written in other languages, including C,C+
+, and Fortran.
HISTORY:
MATLAB was created in the late 1970s by Cleve Molar, then chairman of the
computer science department at the University of New Mexico.[4] He designed it to give
his students access to LINPACKand EISPACKwithout having to learn Fortran. It soon
spread to other universities and found a strong audience within the applied mathematics
community. Jack little, an engineer, was exposed to it during a visit Molar made to
Stanford University in 1983. Recognizing its commercial potential, he joined with Moler
and Steve Bangert. They rewrote MATLAB in C and founded Math Works in 1984 to
continue its development. These rewritten libraries were known as JACKPAC. In 2000,
MATLAB was rewritten to use a newer set of libraries for matrix manipulation,
LAPACK. MATLAB was first adopted by control design engineers, Little's specialty, but
quickly spread to many other domains. It is now also used in education, in particular the
teaching oflinear algebra and numerical analysis, and is popular amongst scientists
involved with image processing.
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MATLAB ADVANTAGES:
1. Matlab is an interpreted language for numerical computation.
2. It allows one to perform numerical calculations, and visualize the results without
the need for complicated and time consuming programming.
3. Matlab allows its users to accurately solve problems.
4. Which produce graphics easily and produce code efficiently.
SOME FEATURES OF MATLAB:
1. Matlab help facilities.
2. Matlab matrices and vectors.
3. Matlab arithmetic operations.
4. Matlab software.
5. Matlab graphics.
6. Matlab data handling.
WHAT IS SIMULINK:
INTRODUCTION:
Simulink is an environment for multidomain simulation and
Model-Based Design for dynamic and embedded systems. It provides an interactive
graphical environment and a customizable set of block libraries that let you design,
simulate, implement, and test a variety of time-varying systems, including
communications, controls, signal processing, video processing, and image processing.
Simulink is integrated with MATLAB, providing
immediate access to an extensive range of tools that let you develop algorithms, analyze
and visualize simulations, create batch processing scripts, customize the modeling
environment, and define signal, parameter, and test data.
Key Features
Extensive and expandable libraries of predefined blocks
Interactive graphical editor for assembling and managing intuitive block diagrams
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Ability to manage complex designs by segmenting models into hierarchies of
design components
Model Explorer to navigate, create, configure, and search all signals, parameters,
properties, and generated code associated with your model
Application programming interfaces (APIs) that let you connect with other
simulation programs and incorporate hand-written code
Embedded MATLAB Function blocks for bringing MATLAB algorithms into
Simulink and embedded system implementations
simulations interpretively or at compiled C-code speeds using fixed- or variable-
step solvers
Graphical debugger and profiler to examine simulation results and then diagnose
performance and unexpected behavior in your design
Full access to MATLAB for analyzing and visualizing results, customizing the
modeling environment, and defining signal, parameter, and test data
Model analysis and diagnostics tools to ensure model consistency and identify
modeling errors Simulation modes (Normal, Accelerator, and Rapid Accelerator)
for running
TOOL BOXES of MATLAB
SIGNAL PROCESSING:
The Signal Processing Blockset extends Simulink with efficient
frame-based processing and blocks for designing, implementing, and verifying signal
processing systems. The blockset enables you to model streaming data and multirate
systems in communications, audio/video, digital control, radar/sonar, consumer and
medical electronics, and other numerically intensive application areas.
Embedded Target for Motorola MPC555:
The Embedded Target for Motorola MPC555 lets you deploy
production code generated from Real-Time Workshop Embedded Coder directly onto
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MPC5xx microcontrollers. You can use the Embedded Target for Motorola MPC555 to
execute code in real time on the Motorola MPC5xx for on-target rapid prototyping,
production deployment of embedded applications, or validation and performance
analysis.
Real-Time Windows Target:
Real-Time Windows Target enables you to run Simulink and
State flow models in real time on your desktop or laptop PC. You can create and control a
real-time execution entirely through Simulink. Using Real-Time Workshop, you generate
C code, compile it, and start real-time execution on Microsoft Windows while interfacing
to real hardware using PC I/O boards. Other Windows applications continue to run during
operation and can use all CPU cycles not needed by the real-time task.
Real-Time Workshop:
Real-Time Workshop generates and executes stand-alone C code for
developing and testing algorithms modeled in Simulink. The resulting code can be used
for many real-time and non-real-time applications, including simulation acceleration,
rapid prototyping, and hardware-in-the-loop testing. You can interactively tune and
monitor the generated code using Simulink blocks and built-in analysis capabilities, or
run and interact with the code outside the MATLAB and Simulink environment.
Real-Time Workshop Embedded:
Real-Time Workshop Embedded Coder generates C code from
Simulink and State flow models that has the clarity and efficiency of professional
handwritten code. The generated code is exceptionally compact and fastessential
requirements for embedded systems, on-target rapid prototyping boards, microprocessors
used in mass production, and real-time simulators. You can use Real-Time Workshop
Embedded Coder to specify, deploy, and verify production-quality software. To let you
make a side-by-side comparison between the capabilities and characteristics of the codegenerated by Real-Time Workshop and Real-Time Workshop Embedded Coder, the
demos for both products have been placed together on the Real-Time Workshop.
SimDriveline:
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SimDriveline extends Simulink with tools for modeling and simulating the
mechanics of driveline (drivetrain) systems. These tools include components such as
gears, rotating shafts, and clutches; standard transmission templates; and engine and tire
models. SimDriveline is optimized for ease of use and speed of calculation for driveline
mechanics. It is integrated with Math Works control design and code generation products,
enabling you to design controllers and test them in real time with the model of the
mechanical system.
SimEvents:
SimEvents extends Simulink with tools for modeling and simulating discrete-
event systems using queues and servers. With SimEvents you can create a discrete-event
simulation model in Simulink to model the passing of entities through a network of
queues, servers, gates, and switches based on events. You can configure entities with
user-defined attributes to model networks in packet-based communications,
manufacturing, logistics, mission planning, supervisory control, service scheduling, and
other applications. SimEvents lets you model systems that are not time-driven but are
based on discrete events, such as the creation or movement of an entity, the opening of a
gate, or the change in value of a signal.
SimMechanics:
SimMechanics extends Simulink with tools for modeling and simulating
mechanical systems. It is integrated with Math Works control design and code generation
products, enabling you to design controllers and test them in real time with the model of
the mechanical system.
Simulink Accelerator:
The Simulink Accelerator increases the simulation speed of your model by
accelerating model execution and using model profiling to help you identify performance
bottlenecks.
Simulink Control Design:
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Simulink Control Design provides advanced functionality for
performing linear analysis of nonlinear models. You can extract linear approximations of
a model to analyze characteristics such as time and frequency responses and pole-zero
dynamics. A graphical user interface (GUI) and programming capabilities reduce the
complexity and time required to develop the linearized models.
Simulink Fixed Point:
Simulink Fixed Point enables the intrinsic fixed-point capabilities of
the Simulink product family, letting you design control and signal processing systems
that will be implemented using fixed-point arithmetic.
Simulink Parameter Estimation:
Simulink Parameter Estimation is a tool that helps you calibrate the
response of your Simulink model to the outputs of a physical system, eliminating the
need to tune model parameters by trial and error or develop your own optimization
routines. You can use time-domain test data and optimization methods to estimate model
parameters and initial conditions and generate adaptive lookup tables in Simulink.
Simulink Report Generator:
The Simulink Report Generator automatically creates documentation
from Simulink and State flow models. You can document software requirements and
design specifications and produce reports from your models, all in a standard format. You
can use the pre built templates or create a template that incorporates your own styles and
standards.
Simulink Response Optimization:
Simulink Response Optimization is a tool that helps you tune design
parameters in Simulink models by optimizing time-based signals to meet user-defined
constraints. It optimizes scalar, vector, and matrix-type variables and constrains multiple
signals at any level in the model. Simulink Response Optimization supports continuous,
discrete, and multirate models and enables you to account for model uncertainty by
conducting Monte Carlo simulations.
Simulink Verification and Validation:
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KEY FEATURES:
Modeling environment for building electrical power system models for AC, DC,
and mixed AC/DC systems
Libraries of application-specific models, including models of common AC and
DC electric drives, Flexible AC Transmission Systems (FACTS), and wind-power
generation
Discretization and phasor simulation modes for faster model execution
Ideal switching algorithm, enabling fast and accurate simulation of power
electronic devices
Analysis methods for obtaining state-space representations of circuits and
computing load flow for machines
Demonstration models of key electrical technologies
MODELING ELECTRICAL POWER STSTEMS:
With SimPowerSystems, you build a model of a system just as you
would assemble a physical system. The components in your model are connected by
physical connections that represent ideal conduction paths. This approach lets you
describe the physical structure of the system rather than deriving and implementing the
equations for the system. From your model, which closely resembles a schematic,
SimPowerSystems automatically constructs the differential algebraic equations (DAEs)
that characterize the behavior of the system. These equations are integrated with the rest
of the Simulink model.
You can use the sensor blocks in SimPowerSystems to measure
current and voltage in your power network, and you can then pass these signals intostandard Simulink blocks. Source blocks enable Simulink signals to assign values to the
electrical variables current and voltage. Sensor and source blocks let you connect a
control algorithm developed in Simulink to a SimPowerSystems network.
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REFERENCES:
[1] L. Chetty, N. M. Ijumba, and A. C. Britten, Parallel-cascaded tapping station, in
Proc. IEEE Int. Conf. Power System Technology, 2004, pp. 16741878.
[2] H. Rahman and B. H. Khan, Power upgrading of transmission line by combining ac-dc transmission,IEEE Trans. Power Syst., vol. 22, no.1, pp. 459466, Feb. 2007.
[3] A. Ekstrom and P. Lamell, HVDC tapping station: Power tapping from a dctransmission line to a local ac network, inProc. AC-DCConf., London, U.K., 1991, pp.
126131.
[4] Task force on SmallHVDCTaps,Working Group, Integration of small taps into
(existing) HVDC links,IEEE Trans. Power Del., vol. 10, no. 3, pp. 16991706, Jul.
1995.
[5] M. R. Aghaebrahimi and R. W. Menzies, Small power tapping from HVDCtransmission system: A novel approach,IEEE Trans. PowerDel., vol. 12, no. 4, pp.16981703, Oct. 1997.
[6] PSCAD/EMTDC, Users Guide Manitoba-HVDC Research Centre. Winnipeg, MB,Canada, Jan. 2003.
[7] P. S. Kundur, Power System Stability and Control. New York: Mc-
Graw-Hill, 1994.