Analysis of STATCOM Performance with Single Phase and ...

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Vol.07,Issue.20,

December-2015,

Pages:4064-4072

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Analysis of STATCOM Performance with Single Phase and Three Phase

Balanced and Un-Balanced Loads KATCHALA Y. N. VENUGOPAL

1, B. KRISHNA

2, V. KAMARAJU

3

1PG Scholar, Dept of EEE, Sanketika Vidya Parishad Engineering College, Visakhapatnam (Dt), AP, India, E-mail:

[email protected]. 2Assistant Professor, Dept of EEE, Sanketika Vidya Parishad Engineering College, Visakhapatnam (Dt), AP, India,

E-mail: [email protected]. 3Assistant Professor, Dept of EEE, Sanketika Vidya Parishad Engineering College, Visakhapatnam (Dt), AP, India.

Abstract: this paper presents an analysis of the three-phase

self excited induction generator (SEIG) with static

compensator (STATCOM) as a voltage regulator. Current

controlled voltage source inverter (CC-VSI) is used as

STATCOM, which provides fast dynamic response to

maintain constant voltage at SEIG terminals during severe

load perturbations and acts as a source and sink of reactive

power. The performance equations are derived sing d-q

variable in stationary reference frame to develop a

mathematical model of SEIG-STATCOM system feeding

unbalanced loads. Transient analysis of the SEIG

STATCOM system is carried out for voltage build-up

switching in STATCOM, application and removal of

balanced/unbalanced resistive/reactive loads. The

STATCOM regulates the SEIG terminal voltage through

reactive power compensation and also suppresses the

harmonics injected by consumer loads. A single-phase

synchronous D-Q frame theory-based control algorithm is

used to generate gating pulses to the three-phase

STATCOM. In this proposed scheme Static Compensator

(STATCOM) is connected at a point of common coupling

with a battery energy storage system (BESS) to

photovoltaic system mitigate the power quality issues. By

using MATLAB/SIMULINK software.

Keywords: Self-Excited Induction Generator (SEIG),

Single Phase Synchronous D-Q Frame Theory, Static

Synchronous Compensator (STATCOM).

I. INTRODUCTION

The proliferation of the power electronics-based

equipment, nonlinear and unbalanced loads, has aggravated

the power quality (PQ) problems in the power distribution

network. They cause excessive neutral currents, over

heating of electrical apparatus, poor power factor, voltage

distortion, and high levels of neutral –to ground voltage,

and inference with communication systems. The literature

records the evolution of different custom power devices to

mitigate the power-quality problems by injecting the

voltages/currents or both in to the system. Power

distribution systems, ideally, should provide their

customers with an uninterrupted flow of energy at smooth

sinusoidal voltage at the contracted magnitude level and

frequency [1]. However, in practice, power systems,

especially the distribution systems, have numerous

nonlinear loads, which significantly affect the quality of

power supplies. As a result of the nonlinear loads, the

purity of the waveform of supplies is lost. This ends up

producing many power quality problems. Apart from

nonlinear loads, some system events, both usual (e.g.

capacitor switching, motor starting) and unusual (e.g.

faults) could also inflict power quality problems [2].Power

quality phenomenon or power quality disturbance can be

defined as the deviation of the voltage and the current from

its ideal waveform.

Many efforts have been taken by utilities to fulfill

consumer requirement, some consumers require a level of

PQ higher than the level provided by modern networks of

electricity. It shows that some measures must be taken in

order to achieve higher levels of Power Quality. The

FACTS devices and Custom power devices are introduced

to electrical system to improve the power quality of the

electrical power. DVR, STATCOM/DSTATCOM, Active

Filters, UPFC, UPQC etc are some of the devices used to

improve the power quality of the current and voltage. By

the help of these devices we are able to reduce the

problems related to power quality. The unbalanced loads

would pose additional problem on the design of controller

that should not only provide needed VAR but also

maintain the generator output voltage and current under

balance in spite of unbalanced load. This paper addresses

this issue and suggests a viable STATCOM based

controller. Here the total system comprising SEIG;

STATCOM and a general balanced/unbalanced load is

modeled and analyzed for transients/dynamic performance

under realistic load conditions for both resistive and

partially reactive load. The simulated results demonstrate

that the use of STATCOM with SEIG has applicability for

three-phase power generation under all types of

balanced/unbalanced loads.

mailto:[email protected]

mailto:[email protected]

KATCHALA Y. N. VENUGOPAL, B. KRISHNA, V. KAMARAJU

International Journal of Advanced Technology and Innovative Research

Volume.07, IssueNo.20, December-2015, Pages: 4064-4072

Fig.1. Schematic Diagram of the SEIG–STATCOM

System Feeding Single-Phase Loads.

II. SYSTEM CONFIGURATION AND PRINCIPLE

OF OPERATION

Fig.1 shows the schematic diagram of the STATCOM

compensated three-phase SEIG feeding single-phase loads.

The system consists of an SEIG driven by renewable

energy-based prime mover. The single-phase consumer

loads are connected across ―a‖ and ―c‖ phases of the SEIG.

A two-level, three-leg insulated-gate bipolar transistor

(IGBT)-based VSI with a self sustaining dc-bus capacitor

is used as a STATCOM. The STATCOM is connected at

point of common coupling (PCC) through filter inductors

as shown in Fig.1. The STATCOM regulates the system

voltage by maintaining equilibrium among the reactive

power circulations within the system. Moreover, the

STATCOM suppresses harmonics injected by nonlinear

loads and provides load balancing while feeding single-

phase loads. The unbalanced load currents in a three-phase

system can be divided into two sets of balanced currents

known as positive sequence components and negative

sequence components.

A. Unit Vector

The control diagram of grid- interfacing inverter for a 3-

phase system is shown in Fig. 2. The main aim of proposed

approach is to regulate the power at PCC during: While

performing the power management operation, the inverter

is actively controlled in such a way that it always draws/

supplies fundamental active power from/ to the grid. If the

load connected to the PCC is non-linear or unbalanced or

the combination of both, the given control approach also

compensates the harmonics, unbalance, and neutral

current. The duty ratio of inverter switches are varied in a

power cycle such that the combination of load and inverter

injected power appears as balanced resistive load to the

grid.

Fig.2. Block diagram representation of grid-interfacing

inverter control.

The regulation of dc-link voltage carries the information

regarding the exchange of active power in between

renewable source and grid. Thus the output of dc-link

voltage regulator results in an active current (Im). The

multiplication of active current component (Im). With

unity grid voltage vector templates (Ua,Ub, and Uc)

generates the reference grid currents . The reference grid

neutral current (I*n) is set to zero, being the instantaneous

sum of balanced grid currents. The grid synchronizing

angle (θ) obtained from phase locked loop (PLL) is used to

generate unity vector template as [9]–[11]

(1)

(2)

(3)

The actual dc-link voltage (Vdc) is sensed and passed

through a first-order low pass filter (LPF) to eliminate the

presence of switching ripples on the dc-link voltage and in

the generated reference current signals. The difference of

this filtered dc-link voltage and reference dc-link voltage

(V*dc) is given to a discrete- PI regulator to maintain a

constant dc-link voltage under varying generation and load

conditions. The dc-link voltage error Vdceer(n) at nth

sampling instant is given as:

(4)

The output of discrete-PI regulator at th sampling

instant is expressed as

(5)

Where KPVdc = 10 and KIVdc = 0.05 are proportional and

integral gains of dc-voltage regulator. The instantaneous

values of reference three phase grid currents are computed

as

(6)

Analysis of STATCOM Performance with Single Phase and Three Phase Balanced and Un-Balanced Loads



(7)

(8)

The reference grid currents (I*a, I

*b, I

*c) are compared

with actual grid currents (Ia, Ib, Ic) to compute the current

errors as

(9)

(10)

(11)

(12)

These current errors are given to hysteresis current

controller. The hysteresis controller then generates the

switching pulses (P1 to P8) for the gate drives of grid-

interfacing inverter. The average model of 4-leg inverter

can be obtained by the following state space equations

(13)

(14)

(15)

(16)

(17)

Where VInva, VInvb, VInvc and VInvn are the three-phase ac

switching voltages generated on the output terminal of

inverter.

These inverter output voltages can be modeled in terms

of instantaneous dc bus voltage and switching pulses of the

inverter as

(18)

(19)

(20)

(21)

Similarly the charging currents VInvad, VInvbd, VInvcd and

Vinvnd on dc bus due to the each leg of inverter can be

expressed as

(22)

(23)

(24)

(25)

The switching pattern of each IGBT inside inverter can

be formulated on the basis of error between actual and

reference current of inverter, which can be explained as:

If IInva < (I*Inva-hb), then upper switch S1will be OFF

(P1 =0) and lower switch S4 will be ON (P4=1) in the

phase ―a‖ leg of inverter.

If IInva > (I*Inva-hb), then upper switch S1 will be ON

(P1 =1) and lower switch S4 will be OFF (P4=0) in the

phase ―a‖ leg of inverter Where hb is the width of

hysteresis band. On the same principle, the switching

pulses for the other remaining three legs can be

derived.

III. PHOTOVOLTAIC (PV) SYSTEM

In the crystalline silicon PV module, the complex physics

of the PV cell can be represented by the equivalent

electrical circuit shown in Fig.3. For that equivalent

circuit, a set of equations have been derived, based on

standard theory, which allows the operation of a single

solar cell to be simulated using data from manufacturers or

field experiments.

Fig.3. Equivalent electrical circuit of a PV module.

The series resistance RS represents the internal losses

due to the current flow. Shunt resistance Rsh, in parallel

with diode, this corresponds to the leakage current to the

ground. The single exponential equation which models a

PV cell is extracted from the physics of the PN junction

and is widely agreed as echoing the behavior of the PV cell

(26)

The number of PV modules connected in parallel and

series in PV array are used in expression. The Vt is also

defined in terms of the ideality factor of PN junction (n),

Boltzmann’s constant (KB), temperature of photovoltaic

array (T), and the electron charge (q). Applied a dynamical

electrical array reconfiguration (EAR) strategy on the

photovoltaic (PV) generator of a grid-connected PV system

based on a plant-oriented configuration, in order to

improve its energy production when the operating

conditions of the solar panels are different. The EAR

strategy is carried out by inserting a controllable switching

matrix between the PV generator and the central inverter,

which allows the electrical reconnection of the available

PV modules.

IV. MATLAB/SIMULINK RESULTS

Simulation results of this paper is as shown in bellow

Figs. 4 to 30.

Case I: For Linear Load




Fig.4.Simulink Circuit for Linear Load.

Fig.5. Source Voltage and Current.

Fig.6 Source Voltage and Load Current.

Fig.7.Simulation Results For Active Power At Source

Side And Load Side.

Fig.4. shows the Matlab/Simulink model of linear load,

fig.5. Shows the Source voltage and current, fig.6. Shows

the three phase Source voltage and load current,

fig.7.shows the active power at source side and load side.

Case II: For Single Phase Non Linear Load

Fig.8.Simulink Circuit for Single Phase Non Linear

Load.

Fig.9.Simulation Results for Source Voltage And

Source Currents.

Fig.10. Simulation Results for Source Voltage, Dc Link

Current, RMS Voltage and Load Current.




Fig.11.Source Voltage and Compensation Currents.

Fig.12.Simulated Results for Input Power Factor.

Fig.13.THD Analysis for Source Voltage.

Case.III. Dynamic Performance of the SEIG–

STATCOM System Feeding Single-Phase Nonlinear

Loads

Fig.14.Simulink Model of Dynamic Performance of the

SEIG–STATCOM System Feeding Single-Phase

Nonlinear Loads.

(a)

( b)

(c)

Fig.15. Dynamic performance of the SEIG–STATCOM

during load removal. (a) vab, icomc, igc and il. (b) vab,

icom a, icomb and icomc. (c) vab, Vdc, icomc and il.




(a)

(b)

(c)

Fig.16. Dynamic performance of the SEIG–STATCOM

during load application. (a) vab , icomc , igc and il . (b)

Vab, icom a, icomb and icom c. (c) Vab, Vdc, icomc and

il.

Case IV: Three Phase Balanced Linear And Non

Linear Load

Fig.17.Simulink circuit for three phase balanced linear

load.

Fig.18.simulation of Source Voltage Three phase

Source Current(ia,ib,ic) for linear load.

Fig.19.Single-phase linear loads Vab, Vdc and VtRMS

and three phase Load Current.




Fig.20.Simulation of Source Voltage Three phase Load

Current(ia,ib,ic) for linear load.

Fig.21.Simulink Circuit for Three Phase Balanced Non-

Linear Load.

Fig.22.Simulation of Source Voltage And Three Phase

Source Current(Ia,Ib,Ic).

Fig.23.Simulation Results for Single Source Voltage

and Three Phase Source Current And Load Current At

Non Linear Load.

Fig.24.Simulation Results for Source Voltage, DC Link

Current, RMS Voltage and Load Current.

Fig.25. Source Voltage and Compensation Currents.




Case V: Three Phase Unbalanced Linear And Non-

Linear Load

Fig.26.Simulink Circuit for Three Phase Unbalanced

Linear Load.

Fig.27.Single-Phase Linear Loads Vab , Vdc And Vtrms

And Three Phase Load Current.

Fig.28.Simulink Circuit for Three Phase Unbalanced

Non-Linear Load.

Fig.29.Single-Phase Linear Loads Vab , Vdc And Vtrms

And Three Phase Load Current.

Fig.30. Source Voltage and Compensation Currents.

V. CONCLUSION

The proposed method of feeding single-phase loads from

a three-phase SEIG and STATCOM combination has been

tested, and it has been proved that the SEIG is able to feed

single phase loads up to its rated capacity. A single-phase

synchronous D-Q frame theory-based control of a three-

phase STATCOM has been proposed, discussed, and

implemented for current balancing of the SEIG system and

different loading conditions.

VI. REFERENCES

[1] E. D. Bassett and F. M. Potter, ―Capacitive excitation

for induction generators,‖ Trans. Amer. Inst. Elect. Eng.,

vol. 54, no. 5, pp. 540–545, May 1935.

[2] J. E. Barkle and R. W. Ferguson, ―Induction generator

theory and application,‖ Trans. Amer. Inst. Elect. Eng.,

vol. 73, no. 1, pp. 12–19, Jan.1954.

[3](2013).[Online].Available: http://www.picohydro.org.uk

[4] N. Smith Motors as Generators for Micro-Hydro

Power. London, U.K.: ITDG Publishing, 1994.




[5] S. Khennas and A. Barnett, ―Best practices for

sustainable development of micro hydro power in

developing countries,‖ World Bank, Washington, DC,

USA, ESMAP Tech. Rep. 21640, no. 6, 2000.

[6] H. Rai, A. Tandan, S. Murthy, B. Singh, and B. Singh,

―Voltage regulation of self excited induction generator

using passive elements,‖ inProc. IEEE Int. Conf. Elect.

Mach. Drives, Sep. 1993, pp. 240–245.

[7] L. Shridhar, B. Singh, and C. Jha, ―Transient

performance of the self regulated short shunt self excited

induction generator,‖IEEE Trans. Energy Convers., vol.

10, no. 2, pp. 261–267, Jun. 1995.

[8] E. Bim, J. Szajner, and Y. Burian, ―Voltage

compensation of an induction generator with long-shunt

connection,‖ IEEE Trans. Energy Convers., vol. 4, no. 3,

pp. 526–530, Sep. 1989.

[9] L. Shridhar, B. Singh, C. Jha, B. Singh, and S. Murthy,

―Selection of capacitors for the self regulated short shunt

self excited induction generator,‖ IEEE Trans. Energy

Convers., vol. 10, no. 1, pp. 10–17, Mar. 1995.

[10] L. Wang and C.-H. Lee, ―Long-shunt and short-shunt

connections on dynamic performance of a SEIG feeding an

induction motor load,‖ IEEE Trans. Energy Convers., vol.

15, no. 1, pp. 1–7, Mar. 2000.

[11] M. B. Brennen and A. Abbondanti, ―Static exciters for

induction generators,‖ IEEE Trans. Ind. Appl., vol. IA-13,

no. 5, pp. 422–428, Sep. 1977.

[12] B. Singh and L. Shilpakar, ―Analysis of a novel solid

state voltage regulator for a self-excited induction

generator,‖ IEE Proc.—Generat., Transmits. Distrib. vol.

145, no. 6, pp. 647–655, Nov. 1998.

[13] S.-C. Kuo and L. Wang, ―Analysis of voltage control

for a self-excited induction generator using a current-

controlled voltage source inverter (CC-VSI),‖ IEE Proc.—

Generat. Transmits. Distrib., vol. 148, no. 5, pp. 431–438,

Sep. 2001.

[14] B. Singh, S. Murthy, and S. Gupta, ―STATCOM-

based voltage regulator for self-excited induction generator

feeding nonlinear loads,‖ IEEE Trans. Ind. Electron., vol.

53, no. 5, pp. 1437–1452, Oct.2006.

[15] G. Dastagir and L. A. C. Lopes, ―Voltage and

frequency regulation of a stand-alone self-excited

induction generator,‖ in Proc. IEEE Electr. Power Conf.,

2007, pp. 502–506.

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