Comparison of two control approaches of static VAr generators for compensating source voltage unbalance in three-phase three-wire systems

This paper discusses voltage unbalance problem caused by the grid. In order to eliminate the voltage unbalance at the point of common coupling (PCC), a static VAr generator (SVG) is introduced into the system. Generally, the SVG only compensates reactive power. But in this paper, it is used to solve voltage unbalance problem. The configuration of the whole system is firstly described. Then two types of control strategies of the whole system, i.e., controlling the SVG operating as a voltage controlled voltage source (VCVS) and controlling the SVG as a current source (VCCS), are analyzed and discussed in detail respectively. And the method for the unbalance component decomposition from three-phase source voltage is also proposed. Furthermore, the relationship between all the parameters and their effect on the performance of the SVG in each scheme are compared and evaluated both in theoretical and simulation methods. In the end, the simulation investigations and experiments on a low voltage prototype were carried out. The results showed that the behavior of the SVG is satisfactory in compensating voltage unbalance of the source. The proposed control strategies and algorithms are verified.