Research On Statcom Current Optimization Method Based On Characteristic Harmonic Elimination

Static Synchronous Compensator (STATCOM) can effectivelycompensate reactive power, restrain voltage fluctuation and eliminatethree-phase imbalance, so as to improve the quality of electrical energy inpower system. However, the traditional direct current control method issusceptible to the dead time of power device, DC side voltage fluctuationand system voltage harmonic, which will decline the current trackingperformance of STATCOM and cause serious distortion of grid-connectcurrent. In order to overcome the shortcomings of the traditional controlmethod, a STATCOM current optimization control method based oncharacteristic harmonic elimination is proposed to optimize thegrid-connceted current waveform and improve the current trackingperformance and operation stability of STATCOM.In the three-phase three-wire symmetric system, it studies themathematical model of STATCOM. Then according to the distributionalfeature of harmonics in STATCOM grid-connected current, a current tracking optimization method based on characteristic harmonicelimination is proposed. In this method, a harmonic compensationfeed-forward is added in the traditional direct current control method. Itachieves selective detection of the characteristic harmonics by thegeneralized coordinate transformation method. Then it reconstructs thePWM modulation wave by harmonic injection method to correct thecurrent waveform distortion and realizes the grid-connected currenttracking performance optimization. In order to improve the accuracy forcharacteristic harmonic compensation and the adaptability to voltagedistortion, an adaptive feed-forward gain adjustment method is alsodesigned. It adopts least mean square (LMS) algorithm to improve theaccuracy of characteristic harmonic compensation and used ADALINEneural network self learning ability to raise the adaptability to voltagedistortion. Finally, MATLAB\Simulink simulation result proves thevalidity of this method.In the three-phase four-wire asymmetric system, firstly the splitcapacitors voltage unbalance problem on the DC side is analysed and asplit capacitors voltage balance control strategy based on zero-sequencecurrent is put forward to meet the requirements of asymmetric loadcompensation. Then, because the generalized coordinate transformationmethod is not suitable for three-phase four-wire system, an adaptivesingle-phase harmonic detection algorithm is designed to achieve the extraction of asymmetric current characteristic harmonics. Finally, thecharacteristic harmonic elimination method is applied into three-phasefour-wire STATCOM, and the STATCOM current tracking optimizationcontrol method for asymmetry compensation is proposed.MATLAB\Simulink simulation result proves the effectiveness of splitcapacitors voltage balance control, asymmetrical compensation andcurrent tracking optimization. It is proved that the compensate effect ofthree-phase four-wire STATCOM is improved further.On the basis of the above research, the STATCOM hardwareplatform is constructed and then the main controller program based on thefloating type DSP is designed. Through the STATCOM deviceexperiments and industrial field tests, it is verified that the developedSTATCOM is capable of tracking dynamic reactive load effectively andaccurately. At the same time, by use of the current tracking optimizationcontrol method based on characteristic harmonic elimination, theSTATCOM output current distortion rate is reduced effectively. With highquality is obtained in the grid-connected current, the compensation effectof STATCOM device is improved further.