analysing the performance of dstatcom in power quality

Analysing the performance ofDSTATCOM in Power Quality

Improvement

Dr. R. Kalaivani , Dr.Vimalakeerthy DevadossDepartment of Electrical & Electronics Engineering

Rajalakshmi Engineering college, Chennai,Nizwa College of TechnologyNizwa, Sultanate of Oman

May 10, 2018

Abstract

Power Quality in Distribution system is often affecteddue to usage of solid state switches. Power quality problemssuch as non-standard voltage, current and frequency at theload side are developed. In this paper an improvement hasbeen made to analyses the role of D-statcom (Distributionstatic compensator) located at load side of the distributionsystem, which can eliminate or overcome the problems ofsource side voltage sag and interruption etc... To maintainthe power system quality the D-statcom will absorb andprovide reactive power to mitigate voltage sag, swell, inter-ruption and improve power factor in various conditions.

Key Words:DSTATCOM, Power Quality, PWM tech-nique

1 Introduction

As commercial and industrial customers become more and more re-liant on high quality and high reliability electric power. Insufficientpower quality can be caused by failures and switching operations

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International Journal of Pure and Applied MathematicsVolume 118 No. 24 2018ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

in the network, which mainly result in voltage dips, interruptions,transients and network disturbances from loads that mainly resultin flicker i.e. fast voltage variations, harmonics, and phase imbal-ance. Momentary voltage sags and interruptions are by the mostcommon disturbances that adversely impact electric customer pro-cess operations in large distribution systems. An increasing demandfor high quality, reliable electrical power and increasing numberof distorting loads may leads to an increased awareness of powerquality both by customers and utilities. The most common powerquality problems today are voltage sags, voltage swell, harmonicdistortion and low power factor. Momentary voltage sags and inter-ruptions are by far the most common disturbances that adverselyimpact electric customer process operations in large distributionsystems. In fact, an event lasting less than one sixtieth of a second(one-cycle) can cause a multimillion dollar process disruption for asingle industrial customer. Several compensation devices are avail-able to mitigate the impacts of momentary voltage sags and inter-ruptions. When PQ problems are arising from nonlinear customerloads, such as arc furnaces, welding operations, voltage flicker andharmonic problems can affect the entire distribution feeder. Sev-eral devices have been designed to minimize or reduce the impact ofthese variations. The primary concept is to provide dynamic capac-itance and reactance to stabilize the power system. This is typicallyaccomplished by using static switching devices to control the capaci-tance and reactance, or by using an injection trans-former to supplythe reactive power to the system. Custom power is formally definedas the employment of power electronic or static controllers in dis-tribution systems rated up to 38 kV for the purpose of supplying alevel of reliability or power quality that is needed by electric powercustomers who are sensitive to power variations. Custom powerdevices or controllers, include static switches, inverters, converters,injection transformers, master control modules and energy storagemodules that have the ability to perform current interruption andvoltage-regulation functions within a distribution system.

A. Proposed system overviewThe key component of the DSTATCOM is a power VSC that is

based on high power electronics technologies. The block diagramin fig 1. is implemented in MATLAB Simulink and the results areevaluated to show the effectiveness of the DSTATCOM.

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International Journal of Pure and Applied Mathematics Special Issue

Figure 1. The basic structure of DSTATCOM

2 POWERQUALITY CONCEPT AND

PROBLEMS

Power quality is the set of limits of electrical properties that allowselectrical systems to function in their intended manner without sig-nificant loss of performance or life. The term is used to describeelectric power that drives an electrical load and the load’s abilityto function properly with that electric power. A perfect power sup-ply would be one that is always available, always within voltageand frequency tolerances and has a pure noise-free sinusoidal waveshape.

Without the proper power, an electrical device (or load) maymalfunction, fail prematurely or not operate at all. There are manyways in which electric power can be of poor quality and many morecauses of such poor quality power. Many power problems originatein the commercial power grid, which, with its thousands of miles oftransmission lines, is subject to weather conditions such as hurri-canes, lightning storms, snow, ice, and flooding along with equip-ment failure, traffic accidents and major switching operations. Also,power problems affecting todays technological equipment are oftengenerated locally within a facility from any number of situations,such as local construction, heavy startup loads, faulty distributioncomponents, and even typical background electrical noise.

Widespread use of electronics in everything from home elec-tronics to the control of massive and costly industrial processes hasraised the awareness of power quality. The study of power qual-ity, and ways to control it, is a concern for electric utilities, largeindustrial companies, businesses, and even home users.

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A. Various Problems of Power QualityPower Quality is Any power problem manifested in voltage, cur-

rent, or frequency deviations that results in failure or disoperationof customer equipments. Power systems, ideally, should providetheir customers with an uninterrupted flow of energy at smooth si-nusoidal voltage at the contracted magnitude level and frequency.However, in practice, power systems, especially the isolated sys-tems, some of the primary source of distortion can be identified asbelow.

The Common Power quality issues harmonics, Voltage sag/swell,flicker, interruptions and transients.

B. Methods to Improve Power QualityFACTS devices are now a reality and will soon change the way

engineers plan and operate power systems. These equipments canbe applied in series, shunt or shunt series in transmission line, andcontrols operation parameters in transmission systems in steadystate and system dynamic behavior in transient state. Types ofcompensators are

• Static Synchronous Compensator (STATCOM)• Static Synchronous Series Compensator(SSSC)• Dynamic Voltage Restorer(DVR)• Unified Power Quality Controller (UPFC)• Distribution Static Compensator (DSTATCOM)MODELING OF DSTACOMA D-STATCOM consists of a two-level VSC, a dc energy storage

device, controller and a coupling transformer connected in shunt tothe distribution network. Fig.2 shows the schematic diagram ofD-STATCOM.

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Figure 2. The basic structure of Series Compensator

A. DSTATCOM TEST SYSTEMElectrical circuit model of Series compensator Test system is

shown in fig 3. It is used to verify the effectiveness of the SeriesCompensator. The simulations were accomplished using Matlabsimulink.

Figure 3. Electrical model of Series Compensator

The test system shown in fig.3. comprises a 220kV, 50Hz trans-mission system, represented by a Thevenin equivalent, feeding intothe primary side of a 3-winding transformer connected in Y/Y/Y,230/11/11 kV. A varying load is connected to the 11 kV, secondaryside of the transformer. A two-level D-STATCOM is connected tothe 11 kV tertiary winding to provide instantaneous voltage sup-port at the load point. A 750 F capacitor on the dc side providesthe D-STATCOM energy storage capabilities. Breaker 1 is used tocontrol the period of operation of the DSTATCOM and breaker 2is used to control the connection of load 1 to the system.

Table 1. System Parameters

3 SIMULATION RESULTS AND DIS-

CUSSIONS

A. Actual system without DSTATCOM

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In this system a three phase input voltage of 220KV per phaseis applied using three single phase supply in Simulink. The lineimpedance is added using the RLC series branch tool. Voltage mea-surement blocks are inserted to measure the value of input voltages.A scope is added to view the waveform of the input voltage. Thethree phase supply voltage is the given to the converter to convertthree phase ac supply into DC supply. Main driver load is con-nected to this DC supply and the voltage measurement block isconnected to measure the voltage. The gate of the converter is sup-plied using a 6 pulse generator. The pulse generator is responsiblefor producing the harmonics in the voltage of the connected system.Measurement block is added to measure voltage and current of thesystem.

Figure 4. MATLAB SimulinkWITHOUT DSTATCOM

B. Modified system with DSTATCOMA voltage source converter fed by a DC supply is used to produce

the 3 phase voltage required to maintain the power quality. Thevoltage measurement block is connected to measure the voltage.The gate of the converter is supplied using a 6 pulse generator. Thepulse generator is responsible for producing the harmonics in thevoltage of the con-nected system. Measurement block is added tomeasure voltage and current of the sys-tem. The voltage generatedby this voltage source converter is connected with the LCL filter toremove the harmonics and the required voltage is injected to thedistribution transformer.

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Figure 5. MATLAB Simulink WITH DSTATCOM

C. Simulation result of line-2 to ground fault

Figure 6. Voltage when single line to ground fault withoutcompensator

Figure 7. Current when single line to ground fault withoutcompensator

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Figure 8. Voltage when single line to ground fault withcompensator

Figure 9. Voltage when line1 to line 2 fault without compensator

Figure 10. Current line1 to line2 fault without compensator

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Figure 11. Voltage when line1 to line2 ground fault withcompensator

Figure 12. Voltage when three phase to ground fault withoutcompensator

Figure 13. Current when three phase to ground fault withoutcompensator

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Figure 14. Voltage when three phase to ground fault withcompensator

D. Result DiscussionsSimulation is performed in two stages. First the simulation is

carried without using the DSTATCOM. Simulation is done for threefault cases.

1. Single phase to ground fault2. Line to Line fault3. Three phase to ground fault.Measurements are taken for fault voltage and current using the

scope. 3phase Fault creating block is used to generate differenttypes of fault. Fault is created at time 2/50 and 4/50 of the sup-ply voltage. Meaning of the setting is fault is created during the0.2 second and is maintained upto 0.8 second. Since the load con-nected with the distribution lines will get damaged during the faultoccurrence, three phase circuit breakers are used to isolate the loadduring the fault duration. Timing of operation of circuit breaker isset same as the timing of the fault creating block. It is observed inthe waveform that the value of voltage and current are disturbedwhenever the fault is triggered in the system. As a result powerquality is disturbed.

DSTATCOM circuit is then simulated to maintain the powerquality. Voltage source inverter is used to create a compensatingvoltage at the time of fault occurrences. When-ever the fault iscreated a gate pulse is triggered to inject the voltage to the distri-bution line using the VSV inverter circuit. LCL filter is used in thecircuit to eliminate or reduce the ripples that are generated by theVSC inverter.

The waveforms of voltage the lines at different fault level is

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taken. It is found that DSTATCOM works effectively in maintain-ing the power quality of a distribution system.

4 CONCLUSION

This paper has presented the power quality problems such as volt-age sags and swell. Compensation techniques of custom power elec-tronic device D-STATCOM was presented. The D-STATCOM hasdemonstrated excellent performance in every case and it canbe con-cluded that D-STATCOM effectively improves the power quality indistribution networks. It is an attractive technology for future ap-plication in the Algerian distribution systems.

The simulation results show that the voltage sags can be miti-gate by inserting DSTATCOM caused due to faults & swell due tosudden switching of loads in the distribution system. The VoltageSource Convert (VSC) was implemented with the help of SinusoidalPulse Width Modulation (SPWM). The control scheme was testedunder a wide range of operating conditions, and it was observedto be very robust in every case. For modeling and simulation of aD-STATCOM by using the highly developed graphic facilities avail-able in MATLAB/SIMULINK were used.

This project shows that D-STATCOM can improve the stabil-ity of energy systems especially in critical operating conditions, andunexpected such as short circuits. The simulations carried out hereshowed that the DSTATCOM provides relatively better voltage reg-ulation capabilities.

References

[1] Roger C. Dugan, Mark f. Mcgranaghan, Dr. Surya Santosoand H. Wayne Beaty., Electrical power systems quality, TataMcGraw Hills publications, 2002.

[2] Devaraju.T, Dr.Veera Reedy.V.C and Dr.Vijayakumar.M,Modeling and simulation of customer power devices to miti-gate power quality problems International Journal of Scienceand Technology, Vol. 2(6), 2010, pp.1880-1885.

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[3] Wang.T.X, Choi S.S. and E.K.K. Sng Series compensationmethod to mitigate harmonics and voltage sags and swells IETGener. Transm. Distrib., Vol. 1, No. 1, January 2007,pp.96-103.

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analysing the performance of dstatcom in power quality

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