Research On Harmonics Elimination And Reactive Power Compensation Applied To Three-phase Four-wire System

There are many methods for the compensation of reactive power and harmoniccurrents. As a compromise between economy and performance, this paper adopts thesystem constructed by APF and SVC to compensate reactive power and harmoniccurrents simultaneously. The SVC is constructed by FC ( fixed capacitor) andTCR( thyristor controlled reactor), and the APF is constructed by a four-leg voltagesource converter. SVC acts as a classic reactive power compensator for loadbalancing and power factor correction, and APF is used to compensate the harmoniccurrent and the neutral current.The control method of using SVC to compensate the reactive power and thefundamental negative-sequence current is detailedly discussed. The whole controlalgorithm is presented. The single phase equivalent model of the SVC system in DQrotating frame is analyzed and the parameters of the PI controller is derived throughthe analysis and synthesis of the system model.The method to detect harmonic currents in the three-phase four-wire system isanalyzed. The dead-beat current control of the APF is obtained based on the analysisof the model of the four-leg voltage source converter. The three-dimensional spacevector modulation for the APF is also detailedly analyzed. The APF has two controlloops. One is the DC voltage outer loop,and the other is the current inner loop. Thewhole control algorithm of the APF is presented.The interaction between APF and SVC is analyzed, and the strategy to improvethe system stability is proposed.The combined system of APF and SVC is simulated accurately using MATLAB.A 5kVA prototype is built and controlled by DSP and CPLD. Simulation results andexperimental results are presented to validate the effectiveness of the controlalgorithm.