The General Mathematical Model and Performance Analysis of Multi-pulse Three-level STATCOM

Static synchronous compensator (STATCOM) is a flexible ac transmission system (FACTS) device for generating or absorbing reactive power. In this paper, the general mathematical model for the multi-pulse three-level STATCOM which consists of m three-phase three-level dc-ac converters connected together through a interphase transformer is proposed by use of the switching function concept. With the assumption of constant dc-link voltage, the harmonic voltage amplitude expressions of three types of the STATCOM under the fundamental frequency modulation (FFM) control are presented and employed to analyze the output voltage harmonic characteristics of the STATCOM. Furthermore, the developed model is implemented and the STATCOM output voltage harmonic spectra are simulated with the help of Matlab/Simulink. Meanwhile, taking the dual three-point STATCOM (m=2) for example, the steady-state and dynamic performance of the STATCOM are investigated by the digital simulation method. Both analytical and simulation results show the STATCOM can compensate the reactive power needed by load effectively and increase the power system stability quickly, and the proposed model is feasible and will be helpful to the design and development of the power electronic system with high voltage and large capacity.