Research On Devices Selection And Control Strategy Of STATCOM Based On MMC

With the rapid development of power electronics technology, it is required for high-power electronic devices in the electricity field of high-voltage, frequency conversion velocity modulation control of high-voltage large motors, HVDC and flexible AC transmission. For resolving high-voltage high-power;(?)nversion, the multi-level transformation techniques have been proposed and get more attention, due to the optimized the output waveform and high conversion efficiency. The modular multi-level as a new multilevel technology opened up a new way for the development of high-voltage high-power converter. Modular multi-level converter (MMC) is a new multi-level voltage converter with module, and it has become one of multi-level converter technology research focus in recent years.In China, it is at an early research stage for studying on MMC used in STATCOM. In this paper, its device selection and control strategies are studied for STATCOM based on the MMC (referred as M-STATCOM), the research results have certain theoretical and practical value for promoting the research and development of the M-STATCOM technology.Firstly, this paper introduces STATCOM technology de elopment process, and leads STATCOM based on the the MMC structure. Its working prlnciple is analyzed from three aspects:anglesthe relationship between the voltage phasors, power control and energy transfer, and it is discussed that its AC side modulation, DC side regulator control method and the module capacitance pressure control mode.It is essential to ensure its reliable operation for reasonable choice of M-STATCOM device structure parameters. In this paper, the operating characteristics are analyzed for its two important components:series reactors and power module, and the selection basis for them are given. It provides hardware conditions to ensure reliable operation of the M-STATCOM devices, and the results of loss calculation for its power module can provide the basis for the selection and design of its cooling device.A circulation suppressor is designed based on the M-CTATCOM system circulation mechanism. It can effectively inhibit doubled circulation component, reduce the rms current in the bridge arm, and decrease the total loss of the M-STATCOM systems. The reactive power compensation control strategy for M-STATCOM is proposed based on instantaneous reactive power theory. And for meeting faster response speed and better control accuracy requirements, M-STATCOM control strategy is design for imbalance compensation based on direct current control. It confirmed that M-STATCOM is not only suitable for reactive power compensation of reactive power; also apply to power quality problems for the three-phase unbalanced system conditions occurred. Simulation results show control strategies and theoretical analysis is effect and correct. M-STATCOM can not only work for reactive power compensation, also can been applied to the comprehensive management for power quality problems of three-phase unbalanced system. Simulation results show the control strategies and theoretical analysis are correct and effective.Finally, on multi-level structures of the three-phase five-level modular inverter experimental platform, control strategy for inhibitory circulation and capacitive pressure control strategy are tested, and the test results confirmed their effectiveness:PWM control theory, module capacitive pressure strategy and circulation suppression strategy.