Research On Optimal Control For DC Side Voltage Of D-STATCOM

In recent years, reactive load and nonlinear load increases, resulting in lower power factor and harmonic pollution. It greatly deteriorates the power supply quality, and causes adverse effects to the safe and economic operation of the distribution network. Distribution static synchronous compensator(D-STATCOM) has the advantages of powerfully adjusting ability, low loss and wide operation range, and it can realize multiple functions of the dynamic reactive power compensation, harmonic suppression and compensation of three phase asymmetrical balance current. With these characteristics, it becomes a hotspot in the field of modern power quality control. The compensation current of D-STATCOM is produced from the difference value between the AC voltage of DC side and power voltage which is produced in filter inductor, so the D-STATCOM current generating capacity and the compensation effect are largely determined by the stability of DC side voltage.This paper introduces the working principle, the topology, the instruction current detection method, the compensating current control and other key technologies of D-STATCOM. Firstly, according to the phenomenon of voltage overshoot and starting inrush current which is easily caused by the conventional PI control of DC side voltage loop, a soft starting mode is designed to reduce the impact of distribution network when D-STATCOM puts into operation; Secondly, in view of the fact that the traditional control has high precision requirements of the mathematical model and poor robustness, a fuzzy PI control strategy which can realize the parameter self-tuning according to the operation condition of DC voltage is proposed. The strategy can decrease fluctuation of the DC side and ensure good performance of the device; Lastly, this article gives a reasonable design idea of the main circuit parameters through formula derivation, providing several references for the practical design of D-STATCOM.The traditional PI strategy and the new fuzzy PI control strategy are compared and analyzed through the D-STATCOM simulation model which is established by MATLAB/SIMULINK. No matter in the steady state or transient operating state, the results show that the new control strategy can effectively stabilize the DC voltage of D-STATCOM, and the compensation effect of harmonic current, reactive power and unbalancing value are all better than the original control strategy.The main circuit parameters, the device control system and the switch dead zone, driving and snubber circuit of IGBT is selected and designed with the proposed design ideas, and the main program of design, the subprogram of detection and control and control are designed based on DSP. Experimental results obtained by developping a 10 KVA D-STATCOM prototype in three-phase four bridge arm show that the proposed control strategy can stablize the voltage of DC side and improve the compensation of D-STATCOM effectively, finally the prototype is connected to the actual system.