A Study On A SVPWM Based ASVG Compensating The Unbalanced System

Advanced static Var Generator (ASVG) is an important FACTS controller, which has applied in power networks home and board. So far, however, people mainly paid their attention to those functions of ASVG , such as compensating reactive power or damping surge of power system. This paper brings forward that ASVG is capable of compensating harmonic, negative sequence and zero sequence currents. So ASVG can synchronously compensate the reactive current and harmful currents in three-phase four-wire unbalanced system. The algorithm of three Dimensions voltage Space Vector Modulation that controls the ASVG is developed. In this paper, the simulation is completed.The main works and conclusions in this paper are as follows: For compensating unbalanced power system,through comparing accustomed structures of main circuit, the main circuit of ASVG advanced in this paper is selected for the first time as a converter with four legs. The dynamic model of ASVG is established, which is regard as bases of transforming the reference currents to the reference voltage. Principle of selecting main model parameters is discussed. Based on the ip-iq method, the reference current signals are detected from load currents.Space Vector Modulation technology with many advantages relative to SPWM, such as nice dynamic response ability, high utilization ratio of DC bus voltage,and convenience of composing digital control system, is adopted to control the ASVG . In this paper, the algorithm of three Dimensions voltage Space Vector Modulation applicable to converter with four legs is developed .Using MAST language of the SABER software, the detection module and 3D SVPWM module are programmed. Simulation on a super high voltage (500kv) unbalanced power transmission system is processed. The results indicate that ASVG not only can compensate reactive currents, but also can effectively filter the harmonic currents, negative sequence currents and zero sequence currents.As one of extremely unbalanced case, operating in two phases is also researched in this paper. In this case, the harmful currents in system can be filtered. It is showed that the ASVG advanced in this paper can realize operating in two phases in high voltage transmission through .