Research On The Control Strategy About Integrated Compensation Applied To The Distribution Networks

There are many methods for the compensation of reactive power and harmonic currents in distribution networks. As a compromise between economy and performance,this paper adopts the system constructed by APF and SVC to compensate reactive power and harmonic currents simultaneously. The SVC is constructed by FC (fixed capacitor) and TCR(thy ristor controlled reactor), and the APF is constructed by a four-leg voltage source converter. SVC acts as a classic reactive power compensator for load balancing and power factor correction. and APF is used to compensate the harmonic current and the neutral current.The control method of using SVC to compensate the reactive power and the fundamental negative-sequence current is detailedly discussed. The whole control algorithm is presented. The single phase equivalent model of the SVC system in DQ rotating frame is analyzed and the parameters of the PI controller is derived through the analysis and synthesis of the system model.The method to detect harmonic currents in the three-phase four-wire system about distribution networks is analyzed. The dead-beat current control of the APF is obtained based on the analysis of the model of the four-leg voltage source converter. The three-dimensional space vector modulation for the APF is also detailedly analyzed. The APF has two control loops. One is the DC voltage outer loop,and the other is the current inner loop. The whole control algorithm of the APF is presented.The interaction between APF and SVC is analyzed, and the strategy to improve the system stability is proposed.The combined system of APF and SVC is simulated accurately using MATLAB. Simulation results are presented to validate the effectiveness of the control algorithm.It is improved the unbalance system. After compensating, the power factor of system nears 1, the THD declines to 5%.