Modulation, Simulation, Control And Experiment Of M-Statcom

This dissertation is a part of the large research project, financed by National Science Foundation of China (NSFC). It is dedicated to a comprehensive study of static synchronous compensator (STATCOM) systems utilizing state-of-the-art modular multilevel converter (M2C) called M-STATCOM. With the rapid development and popularity of power electronics technology, some industry loads such as single phase AC traction system and electric arc furnaces etc. cause increasing power quality problems featured with harmonic distortion, low power factor, and phase imbalances to the utility grids. Such power quality problems produce some unexpected disturbances in operation of electrical equipments which share the same distribution feeder with these nonlinear loads. The comprehensive compensation of the nonlinear, poor power factor, and/or unbalanced loads is an important issue in the modern power system. Many techniques have been proposed to improve the grid side power factor and voltage imbalance, and to cancel out the harmonics generated by power electronic loads. Among flexible AC transmission system (FACTS) controllers, the STATCOM is found feasible to provide precise and flexible control to mitigate disturbances and effectively improve power quality as well as it is cost effective in a wide range of problem-solving abilities from transmission to distribution levels. Referring to the literature reviews, the M2C is clearly the most feasible topology for use as a power converter in the STATCOM applications. The control of M-STATCOM is not very complicated.The multilevel STATCOM compared to the traditional STATCOM reduces cost by eliminating transformer, improves the output waveform and has a lot of advantages. The state-of-the-art M2C is a promising converter technology for various high-voltage high-power applications. The reason to this is that low-distortion output quantities can be achieved with low average switching frequencies per switch and without output filters. It has extremely vital significance in STATCOM research.In this thesis, three phase10kV,15level M-STATCOM topology and its basic principle is studied. Using M2C's single-phase equivalent circuit, its detailed mathematical analysis including steady state and transient analysis of the circulation current is presented. Direct current control method is adopted to modify the traditional capacitor voltage balance strategy. For high accuracy and good control system response purpose Level-shift sine pulse width modulation (LSPWM) technique is selected as the modulation strategy. Carrier-Based Modulation Techniques for M2C and Classification of the most common modulation techniques are discussed.A three phase10kv,9-levels modular multilevel converter (M2C), both for basic-level mode (N+1) and full-level mode (2N+1) levels, is simulated in MATLAB/ENVIRONMENT and harmonic analysis (THD) of waves are also discussed. Then a three-phase10kv,15-level STATCOM based on this M2C (M-STATCOM) is also simulated in the same software in order to analyze its static and dynamic characteristics. The simulation results verify the validity of the proposed control algorithm.In order to verify the accuracy of the proposed model and the performance of the control system for the M-STATCOM, a hardware prototype is implemented. The key control procedures are performed by a main controller, which consists of a DSP and an FPGA. The simulation and experimental results indicate the superior performance of the proposed control system, as well as the precision of the proposed models.