Study Asymmetrical Control Strategy Of Distribution Static Synchronous Compensator

DSTATCOM is in great need in research on modern static reactive power compensation because it is the important reactive power compensation device in customer power system, especially with bidirectional compensate timely. For compensating reactive power and harmonic, negative-sequence and zero-sequence current in distribution power system, this paper studies control method of DSTATCOM under ideal and asymmetrical source voltage. The main works are as follows:After the mathematic model of four-leg inverter is deduced, this paper studies the principle of three-dimensional space vector modulation (3-D SVM), which is the basis of three-level 3-D SVM. The PSCAD/EMTDC simulation results indicate that this control strategy can compensate unbalanced load.Under ideal source voltage, this paper studies the control method of DSTATCOM. NPC inverter is selected as main circuit. According to its equivalent circuit, the math model is established. The p-q-o theory based on the instantaneous reactive power theory is applied to detect the reference current. Then, a fast and generalized applicable 3-D SVM is proposed for controlling NPC inverter. The reference voltage vector is decomposed into an offset vector and a two-level vector in the proposed 3-DSVM control strategy. So identification of neighboring vectors and dwell times calculation are all settled by a general two-level 3-D SVM control. The complicated three-level 3-D SVM issue is simplified to a general two-level 3DSVM issue. The effectiveness of this control algorithm of DSTATCOM has been verified by PSCAD/EMTDC under three conditions. The result of DSTATCOM with unbalanced and non-linear loads proves that the validity of the proposed 3-D SVM can be applied to compensate power quality problems in three-phase four-wire system. The testing method of positive order, negative order and naught order components of the three-phase asymmetric voltage are analyzed in this paper. The proposed approach is based on the rotating coordinate transformations. Through analyzing decomposition of reference voltage vectors, the switches of main circuit are driven. The effectiveness of this control algorithm of DSTATCOM has been verified by PSCAD/EMTDC under three conditions. The result of DSTATCOM with unbalanced, non-linear loads and load switched shows that the validity of the proposed 3-D SVM not only can compensate unbalanced load, harmonic current, but also can minimize unbalance degree of source voltage. The DSTATCOM has good performance at steady state accuracy and dynamic response.