Enhancement Of Power Quality For Transmission System By UPQC

Ass. Prof-Jaya Gopinath Wagh. M.E Electrical power system

Arts, Science and Commerce College CIDCO

Uttamnagar, CIDCO, Nashik-422008 Maharashtra

E-mail: jaya89.wagh@gmail.com

ABSTRACT

In the an improved Unified Power Quality Conditioner (iUPQC), for power factor compensation, voltage and current harmonics compensation, voltage sag and swell compensation, grid side bus voltage regulation and load bus voltage regulation for the combinations of linear and non-linear loads. The iUPQC will work as both STATCOM and conventional UPQC compensation, at the grid side and at the load side respectively. The iUPQC controller composes of PLL and PWM controller which is used for generating reference signal for shunt converter and also the Proportional Integral Derivative controller (PID) which is used for generating reference signal for series converter.

Now a day’s power physics devices square measure used attributable to technological improvement. The increasing variety of power physics hundreds typically utilized in trade attributable to this load power quality downside arises. in line with this thought of power electronic load need ideal curved offer voltage for correct system operation. they're to blame for condition in distribution system. in line with this state of affairs completely different mitigating technique square measure enforced over the years. a number of resolution involves versatile compensator called improved unified power quality controller .by victimization this controller we will compensate voltage sag/swell. conjointly offer reactive power .This paper presents new management technique for iupqc. in this pulse breadth modulation management is employed in it .it is achieved by victimization voltage and current curved references.

The experimental results verified by victimization improved unified power quality controller. The grid-

voltage regulation was achieved by taking completely different load conditions. These results have incontestable an appropriate performance of voltage regulation at either side of the iUPQC, even whereas compensating harmonic current and voltage imbalances.

Keywords: power quality voltage sag, voltage swell. iUPQC; Micro-grids; Power quality; STATCOM; Unified Power Quality Conditioner

INTRODUCTION

The employment of equipment, like data technology instrumentality, power physics like variable speed drives, programmable logic controllers, and energy economical lighting semiconductor diode, static rectifier, converters to a whole modification of electrical hundreds nature .according to this thought , poor power quality might arises that result into exaggerated power losses, abnormal and undesirable performance of equipment’s. In power grid numbers of power quality issues square measure occurred like voltage disturbance, current disturbance, voltage sag, voltage swell, harmonics and reactive power disturbance. thus consumer’s premises it's necessary to attenuate these issues. . improve the voltage profile, stability of system, sweetening of power quality and dependableness of power etc. the assorted versatile AC gear square measure are available electrical network. The FACTS based mostly application of power electronic devices effective for the ability distribution systems to reinforce the standard and also the dependableness of power fed to the shoppers. The FACTS technology consists of high power physics devices. By victimization this Facts device we will implement system stability. thus iupqc is one in every of the most effective solutions of degrading higher than downside.

The circuit of a iupqc consists of a mixture of a shunt active filter and a series active filter connected in a very succeeding configuration. this mixture permits the compensation of the load current and also the offer voltage. Here we have a tendency to contemplate electrical system with 2 buses i.e., bus A and bus B. Bus A could be a bus of the ability system .Bus B could be a bus of the small grid, wherever nonlinear hundreds square measure connected, which needs premium-quality power offer. Our aim is to urge the voltages at buses A and B should be regulated so as to properly offer the sensitive hundreds and also the nonlinear hundreds.This paper presents a new connection for a UPQC called interline UPQC (IUPQC). The single-line diagram of an IUPQC connected distribution system is shown in Fig. 1.

Fig.1: Single-line diagram of an IUPQC-connected distribution system.

Two feeders, Feeder-1 and Feeder-2, which are connected to two different substations, supply the system loads L-1 and L-2. The supply voltages are denoted byVs1 and Vs2 It is assumed that the IUPQC is connected to two buses B-1 and B-2, the voltages of which are denoted by Vt1 and Vt2 respectively. Further two feeder currents are denoted by is1 and is2 while the load currents are denoted by il1 and il2. The load L-2 voltage is denoted by vt2. The purpose of the IUPQC is to hold the voltages Vt1 and Vt2 constant against voltage sag/swell, temporary interruption in either ofthe two feeders. It has been demonstrated that the IUPQC can absorb power from one feeder(Feeder-1)

System quantities

Values

System fundamental

50Hz

frequency (f)

Voltage source Vs1

11kV (L-L, rms), phase angle 0⁰

Voltage source Vs2

11kV (L-L, rms), phase angle 0⁰

Feeder-1 (Rs1+j2πfLs1)

Impedance : 6.05+j36.28Ω

Feeder-2 (Rs2+j2πfLs2)

Impedance : 3.05+j18.14Ω

Load L-11

Phase – a 24.2+j60.50Ω

Phase – b 36.2+j78.54Ω

Unbalanced RL

Phase – c 48.2+j94.25Ω

Component

Load L-12

A three phase diode rectifier that

Non-linear component

supplies a load of 250+j31.42Ω

Balanced load L-2

72.6+j54.44Ω

impedance

to hold Vt2 constant in case of a sag in the voltage Vs2 this can be accomplished as the two VSCs are supplied by a common dc capacitor. The dc capacitor voltage control has been discussed here along with voltage reference generation strategy. Also, the limits of achievable performance have been computed. The performance of the IUPQC has been evaluated through simulation studies using MATLAB.

1.SYSTEM DESCRIPTION WITH METHODOLOGY

For understanding the applicability of the improved iUPQC controller. An electrical system with two buses, bus A and bus B. Bus A of the power system, suppliessensitive loads and serve up point of coupling of a microgrid. At bus B non- linear loads are connected, which requires premium quality power supply, is a bus of the microgrid. The voltages at bus A and bus B should be regulated in order to supply properly the sensitive loads and the non-linear loads. If using a STATCOM, it gives only voltage regulation at bus A not mitigate harmonic currents drawn by the non-linear loads. On the other hand, if using UPQC between bus A and bus B, it can only compensate the harmonic currents of the non-linear loads and compensate the voltage at bus B, but it cannot regulate the voltage at bus A. Hence, to accomplish all the desired goals, a STATCOM at bus A and a UPQC between bus A and B should be employed. However the cost of this solution would be excessiveAn attractive solution is the use of a modified iUPQC controller to provide beside all those functionalities of this equipment and also reactive power support to the bus A. The modified iUPQC can provide the following functionalities:

· It controls the energy and power flow between the grid and the microgrid.

· It provides voltage/frequency support at bus B of the microgrid.

· It provides reactive power support at bus A of the power system.

· It provides harmonic voltage and current isolation between bus A and bus B.

· It provides good breaker as associate degree intertie between the grid and also the small grid.

· It provides voltage and current imbalance compensation..

An IUPQC connected to a distribution system is shown in Fig. 4. during this figure, the feeder impedances area unit denoted by the Pairs (Rs1, Ls1) and (Rs2, Ls2). It may be seen that 2|the 2} feeders offer the masses L-1 and L-The load L-1 is assumed to own two separate components-an unbalanced half (L-11) and a non-linear half (L-12). The currents drawn by these 2 masses area unit denoted by it11 and it12 severally. we tend to additional assume that the load L-2 could be a sensitive load that needs uninterrupted and controlled voltage. The shunt VSC (VSC-1) is connected to bus B-1 at the top of Feeder-1, whereas the series VSC (VSC-2) is connected at bus B-2 at the top of Feeder-2. The voltages of buses B-1 and B2 and across the sensitive load terminal area unit denoted by Vt1 and Vt2 severally. The aim of the IUPQC is two-fold:

· To protect the sensitive load L-2 from the disturbances occurring within the system by regulation the voltage (Vt2).

· To regulate the bus B-1 voltage Vt1 against sag/swell and or disturbances within the system.

In order to achieve these aims, the shunt VSC-1 is operated as a voltage controller whereas the series VSC-2 regulates the voltage Vt2 across the sensitive load. The system parameters employed in the study area unit given in Table I. The length of Feeder-1 is indiscriminately chosen to be double that of Feeder-2. The voltage of bus B-1 and cargo L-1 currents, once no IUPQC is connected to the distribution system, area unit shown in Fig. 5.

Table:1 System Parameters during this figure and altogether the remaining figures showing 3 part waveforms, the phases a, b and c area unit delineate by solid, broken and dotted lines, severally. It may be seen from Fig. 5(a) that because of the presence of unbalanced and non-linear masses L-1, the voltage Vt1 is each unbalanced and distorted. Also, the load L-11 causes associate degree unbalance within the current it12 whereas load L-12 causes distortion within the current it11. we tend to shall currently demonstrate however these waveforms may be improved victimisation the Interline Unified Power Quality Conditioner (IUPQC).

2. IUPQC CONFIGURATION

The improved unified power quality conditioner consists of Shunt active filter and series active filter. it's nothing but the blending of series ad shunt active power filters, that unit of measurement connected in back to back by a typical DC electrical device .

Fig 2 .iUPQC configuration

Fig.2shows the circuit of iupqc, for input signals we've to ponder the voltages and currents measurements for iUPQC controller. The iUPQC controller consists of two PWM converters connected succeeding through a typical dc link. three single-phase transformers unit of measurement utilised to insert the series device between the flexibility system and conjointly the load. The convenience of victimization or not shunt device is further related to economical issues regarding voltage/current levels and power ratings of the system and power converters of the iUPQC the iUPQC contains a easier controller and reduced style of measurements. exclusively the system voltage, the dc-link voltage and conjointly the load current unit of measurement necessary as inputs to the iUPQC controller.

3. OPERATION PRINCIPLE

Fig 3.Operating Principle of Iupqc.

Fig.3shows the principles of the iUPQC. The shunt active filter generates a basic positive-sequence voltage at face price. the compensated load is provided below regulated, curvilinear and balanced voltage conditions (vL). On the other hand, the series active filter imposes a basic positive-sequence current (iS) to be drained from the network. In steady state, the series active filter drains a positive-sequence current in section with the essential positive-sequence component of the availability voltage vS. The magnitude of iS correspond to the common active power demanded by the load, and an energetic current component to create amends for losses inside the iUPQC. Since the shunt active filter of the iUPQC behaves as an ideal voltage offer, it offers ideally null resistance for harmonic currents, whereas the series active filter offers ideally infinite resistance, in line with this thought all harmonic current injected by nonlinear load area unit progressing to be forced to follow in to shunt active filter of iupqc and it provides reactive power of the load, series filter drains exclusively active portion of load current. 4.STRUCTURE &MANAGEMENT

The IUPQC shown in Fig. one consists of 2 VSCs (VSC-1 and VSC-2) that area unit connected back to back through a typical energy storage dc electrical condenser Center for Disease Control and Prevention. allow us to assume that the VSC-1 is connected in shunt to Feeder-1 whereas the VSC-2 is connected asynchronous with Feeder-2. every of the 2 VSCs is completed by 3 H-bridge inverters.

Fig.4: Schematic structure of VSC.

Fig.5: Complete structure of an IUPQC.

Fig.6: Typical IUPQC connected in distribution System

The schematic structure of a VSC is shown in Fig. 4. during this structure, every switch represents an influence semiconductor unit (e.g., IGBT) associate degreed an anti-parallel diode as shown in Fig. 4. All the electrical converters area unit equipped from a typical single dc electrical condenser Center for Disease Control and Prevention and every inverter incorporates a electrical device connected at its output. the whole structure of a three-phase IUPQC with 2 such VSCs is shown in Fig. 5. The secondary (distribution) sides of the shunt-connected transformers (VSC-1) area unit connected in star with the neutral purpose being connected to the load neutral. The coil of the series-connected transformers (VSC-2) area unit directly connected asynchronous with the bus B-2 and cargo L-2. The ac filter capacitors Cf and Ck and also are connected in every part (Fig. 5) to forestall the flow of the harmonic currents generated because of switch. The six inverters of the IUPQC area unit controlled severally. The switch action is obtained victimisation output feedback management. The controller is meant in discrete-time victimisation pole-shifting law within the polynomial domain as mentioned in Appendix A.

5. IUPQC CONTROLLER

The controller of the iUPQC is very simple. it's supported the p-q Theory. A basic a neighborhood of this controller is that the synchronizing circuit supported a district Locked-Loop (PLL), that tracks accurately the frequency and purpose of the essential positive-sequence part of the supply voltage Vs. Fig. shows the complete management diagram of the iUPQC controller. Since the present approach of iUPQC is meant for application in three-phase three-wire systems (without neutral conductor), zero-sequence components unit of measurement out of interest. Hence, simplified 2x2 matrixes of the Clarke Transformations and a reduced numbers of measurements could also be used as input signals for the iUPQC controller.

Fig.7. Iupqc controller

6.FUZZY LOGCONTROLLERS

The word Fuzzy suggests that unclearness. opacity happens once the boundary of piece of knowledge isn't clear-cut. In 1965 LotfiA.Zahed propounded the fuzzy pure mathematics. Fuzzy pure mathematics exhibits vast potential for effective resolution of the uncertainty within the downside. Fuzzy pure mathematics is a superb mathematical tool to handle the uncertainty arising thanks to unclearness. Understanding human speech and recognizing written characters ar some common instances wherever opacity manifests. Fuzzy pure mathematics is associate extension of classical pure mathematics wherever components have variable degrees of membership. formal logic uses the complete interval between zero and one to explain human reasoning. In FLC the input variables ar mapped by sets of membership functions and these ar referred to as as “FUZZY SETS”.

Fig.8.Fuzzy Basic Module

Fuzzy set includes from a membership operate that might be defines by parameters. the worth between zero reveals a degree of membership to the fuzzy set. the method of changing the crisp input to a fuzzy worth is termed as “fuzzification”. The output of the fuzzier module is interfaced with the foundations. the essential operation of FLC is made from fuzzy management rules utilizing the values fuzzy sets generally for the error, amendment of error action. The results ar combined to offer a crisp output, dominant the output variable and this method is termed “defuzzification”.

formal logic management Rules:

Fig.9: management Strategy supported forty nine Fuzzy management rules with combination of seven error states multiplying with seven changes of error states.

Fig. 10. Simulation diagram

Fig. 10a.Fig. 10a. iUPQC response at no load condition: (a) grid voltages VA, (b) load voltages VB, and (c) grid currents

Fig. 10b..iUPQC fugacious response throughout the association of a threephase diode rectifier: (a) load currents, (b) gridcurrents, (c) load voltages and (d) grid voltages.

Fig.10c. iUPQC fugacious response throughout the association of a twophase diode rectifier: (a) load currents, (b) supply currents, (c) load voltages, and (c) supply voltages

The main blessings of the iUPQCar power quality enhancements like power issue correction, voltage and current harmonics mitigation, voltage sag and swell compensation, voltage regulation. The iUPQC keeps clear the disturbances that affects the system, by natural disturbance mitigation. Since the iUPQC provides grid voltage regulation, thus it reduces the inner loop current power within the iUPQC, this can be another power quality compensation feature. The performance of iUPQC are often additional improved by victimisation higher controller in situ of pelvic inflammatory disease controller.

7.CONCLUSION

The paper illustrates the operation associated management of an interline unified power quality conditioner (IUPQC). The device is connected between 2 feeders returning from totally different substations. associate unbalanced and non-linear load L-1 is provided by Feeder-1 whereas a sensitive load L-2 is provided through Feeder-2. the most aim of the IUPQC is to control the voltage at the terminals of Feeder-1 and to safeguard the sensitive load from disturbances occurring upstream. The performance of the IUPQC has been evaluated below numerous disturbance conditions like voltage sag in either feeder, fault in one in all the feeders and cargo amendment. The IUPQC mentioned within the paper is capable of handling system during which the masses ar unbalanced and distorted. As so much because the common dc link voltage is at the affordable level, the device works satisfactorily. The angle controller ensures that the important power is drawn from Feeder-1 to carry the dc link voltage constant. Therefore, even for voltage sag or a fault in Feeder-2, VSC-1 passes real power through the dc capacitance onto VSC-2 to control the voltage Vt2. Finally once a fault happens in Feeder-2 or Feeder-2 is lost, the facility needed by the Load L-2 is provided through each the VSCs. this means that the facility semiconductor switches of the VSCs should be rated such the full power transfer through them should be attainable. within the IUPQC configuration mentioned during this paper, the sensitive load is totally protected against sag/swell and interruption. lastly, the performance below a number of the most important considerations of each client and utility e.g., harmonic contents in hundreds, unbalanced hundreds, provide voltage distortion, system disturbances like voltage sag, swell and fault has been studied. The IUPQC has been shown to complete many of those events with success.

REFERANCE

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[5]Karanki K, G Geddada, MK Mishra, metal Kumar (2013). A changed Three-Phase Four-Wire UPQC Topology with Reduced DC-Link Voltage Rating. IEEE Trans. Ind. Electron. 60(9): 3555-356.