Simultaneous Microgrid Voltage and Current Harmonics Compensation Using Coordinated Control of Dual-Interfacing-Converters
Abstract
The growing installation of distributed generation(DG) units in low voltage distribution systems has popularizedthe concept of nonlinear load harmonic current compensationusing multi-functional DG interfacing converters. It is analyzedin this paper that the compensation of local load harmoniccurrent using a single DG interfacing converter may cause theamplification of supply voltage harmonics to sensitive loads,particularly when the main grid voltage is highly distorted. Toaddress this limitation, unlike the operation of conventionalunified power quality conditioners (UPQC) with series converter,a new simultaneous supply voltage and grid current harmoniccompensation strategy is proposed using coordinated control oftwo shunt interfacing converters. Specifically, the first converteris responsible for local load supply voltage harmonicsuppression. The second converter is used to mitigate theharmonic current produced by the interaction between the firstinterfacing converter and the local nonlinear load. To realize asimple control of parallel converters, a modified hybrid voltageand current controller is also developed in the paper. By usingthis proposed controller, the grid voltage phase-locked loop andthe detection of the load current and the supply voltageharmonics are unnecessary for both interfacing converters.Thus, the computational load of interfacing converters can besignificantly reduced. Simulated and experimental results arecaptured to validate the performance of the proposed topologyand the control strategy.
EXISTING SYSTEM:
Previous research mainly focused on the control of a singleDG shunt interfacing converter as an APF, as their powerelectronics circuits have similar topology. To realize anenhanced active filtering objective, the conventional currentcontrol methods for grid-tied DG interfacing converter shallbe modified. First, the wide bandwidth current controllers areused so that the frequencies of harmonic load current can fallinto the bandwidth of the current controller. Alternatively, theselective frequency harmonic compensation usingmulti-resonant current controller has received a lot ofattenuations, as reported, thedeadbeat controller is developed for multiple DG units withactive harmonic filtering capability. In , the neuralnetwork method is used to improve the harmonic filteringperformance of DG interfacing converters that are connectedto a grid with large variation of grid impedance. In addition tothe compensation of harmonics at low voltage distributionnetworks, the active filtering of harmonics in higher voltagedistribution system using multi-level converters is discussed,as show in. However, it is important to note thatabovementioned compensation methods are mainly used ingrid-tied converter systems. In recent literature, the hybridvoltage and current control is also developed to realize afundamental voltage control for DG power regulation and aharmonic current control for local load harmoniccompensation. Compared to the aforementioned conventionalcurrent control methods, the hybrid controller allows aninterfacing converter to compensate harmonics in bothgrid-tied and islanding micorgrids. With assistance of the lowbandwidth communications between DG units, it alsopossible to achieve harmonic power sharing a parallelDG systems.
PROPOSED SYSTEM:
To realize simultaneous mitigation of the grid current andthe supply voltage harmonics, this paper develops aparallel-converter topology where the local nonlinear load isdirectly installed to the shunt filter capacitor of the firstconverter. The local load supply voltage quality is enhancedby the first interfacing converter through harmonic voltage control. The harmonic current produced by the interactionsbetween the local nonlinear load and the first converter isthen compensated by the second converter. To reduce thecomputational load of the dual-converter system, a modifiedhybrid voltage and current control method is proposed forparallel interfacing converters. With cooperative operation oftwo converters, the load current and supply voltage harmonicextraction and the phase-locked loops are not needed torealize this proposed comprehensive power quality controlobjective. Note that this paper focuses on the compensationof supply voltage and grid current harmonics. When there aresignificant disturbances in the main grids, such as sags/swellsand interruptions, the shunt converter is less effective tocompensate these grid issues. Thus in these cases, theprotection and the fault-ride through control schemes for aconventional single converter can be applied to thisdual-converter in a similar manner.
CONCLUSION
When a single multi-functional interfacing converter isadopted to compensate the harmonic current from localnonlinear loads, the quality of supply voltage to local loadcan hardly be improved at the same time, particular when themain grid voltage is distorted. This paper discusses a novelcoordinated voltage and current controller for dual-convertersystem in which the local load is directly connected to theshunt capacitor of the first converter. With the configuration,the quality of supply voltage can be enhanced via a directclosed-loop harmonic voltage control of filter capacitorvoltage. At the same time, the harmonic current caused by thenonlinear load and the first converter is compensated by thesecond converter. Thus, the quality of the grid current and thesupply voltage are both significantly improved. To reduce thecomputational load of DG interfacing converter, thecoordinated voltage and current control without using loadcurrent/supply voltage harmonic extractions or phase-lockloops is developed to realize to coordinated control of parallelconverters.
REFERENCES
[1] B. Singh, K. AI-Haddad, A. Chandra, “A review of activefilters for power quality improvement,” IEEE Trans. Ind.Electron., vol. 46, no. 5, pp. 960 – 971, May. 1999.
[2] P. Acuna, L. Moran, M. Rivera, J. Dixon, and J. Rodriguez,“Improved active power filter performance for renewablepower generation systems,” IEEE Trans. Power Electron., vol.29, no.2, pp. 687-694, Feb. 2013.
[3] Y. W. Li, F. Blaabjerg, D. M. Vilathgamuwa, and P. C. Loh,“Design and Comparison of High PerformanceStationary-Frame Controllers for DVR Implementation,” IEEETrans. Power Electron., vol. 22, pp. 602-612, Mar. 2007.
[4] C. Meyer, R. W. DeDoncker, Y. W. Li, and F. Blaabjerg,“Optimized Control Strategy for a Medium-Voltage DVR –Theoretical Investigations and Experimental Results,” IEEETrans. Power Electron., vol. 23, pp. 2746-2754, Nov. 2008.
[5] F. Blaabjerg, Z. Chen, and S. B. Kjaer, “Power electronics asefficient interface in dispersed power generation systems,”IEEE Trans. Power Electron., vol. 19, pp. 1184-1194, Sep.2004.
[6] A. Timbus, M. Liserre, R. Teodorescu, P. Rodriguez, and F.Blaabjerg, “Evaluation of current controllers for distributed power generation systems,” IEEE Trans. Power Electron., vol.24, no. 3, pp. 654–664, Mar. 2009.
[7] J. M. Guerrero, L. G. Vicuna, J. Matas, M. Castilla, and J.Miret, “A wireless controller to enhance dynamic performanceof parallel inverters in distributed generation systems,” IEEETrans. Power Electron., vol. 19, no. 4, pp. 1205-1213, Sep,2004.
[8] J. M. Guerrero, J. C. Vasquez, J. Matas, L.G. de Vicuna, and M.Castilla, “Hierarchical control of droop-controlled AC and DCmicrogrids – A general approach toward standardization,” IEEETrans. Ind. Electron., vol. 55, no. 1, pp. 158 – 172, Jan. 2011.
[9] J. He and Y. W. Li, “Analysis, design and implementation ofvirtual impedance for power electronics interfaced distributedgeneration,” IEEE Trans. Ind. Applicat., vol. 47, no. 6, pp.2525-2038, Nov/Dec. 2011.