Research On Static Var Generator Based On Cascade H-Bridge

With the development of power electronics, power electronic devices more and more, use more frequently, which results to low power factor problem. The emergence of Static Var Generator achieves the dynamic function of compensating reactive power, a way to stabilize power grid voltage, reduce equipment capacity and reduce power loss.In conventional SVG (Static Var Generator, SVG), power device switching frequency due to the restrictions, it is difficult to achieve high power. In order to overcome the contradiction between the switching frequency of power device and power capacity in the traditional SVG, a new kind of SVG, based on Cascade, is proposed in the dissertation.SVG designed in this paper uses the topology of Cascade H-Bridge Multi-level Converter,which uses a few switching devices, controls and packes more conveniently; control strategy adopts Carrier phase-shifted SPWM, which is applicable to Cascade H-Bridge Multi-level Converter (Carrier phase-shifted SPWM, CPS-SPWM).This paper introduces the research background of SVG, working principle, then briefly describes the various multi-level converter topology. On this basis, the paper focuses on the Cascade H-Bridge Multi-level Converter topology, the advantages and its application in SVG. Subsequently, the modulation principle and modulation characteristics of the CPS-SPWM modulation strategy are introduced and analysis of CPS-SPWM modulation strategy in the Cascade H-bridge Multi-level Converter application and a simulation study is conducted. The SVG designed in the dissertation adopt the control strategy based on instantaneous reactive power voltage and two closed loop, which can quickly follow the voltage changes, controlling the output of SVG.Finally, based on the conditions of laboratory, experiments about PWM rectifier are designed and conducted, including sigle closed loop experiment and t two closed loop experiment, and the results are compared.