Research On Suppressing Common Mode Voltage Of Multilevel Converter In Wind Power System

As the problems of energy lack and environment pollution are more and more serious,green renewable energy has become a global focus. And wind power industry as an importantpart of new energy has been rapid development. In recent years, with the amplification ofwind generator single capacity, the traditional two level converter already can not meet therequirements, it makes multilevel converter is gradually applied to wind power generationsystem for the feature of large capacity, superior harmonic characteristics, flexible controlmethod etc. During the operation of the converter, as the action of switching device, there iscommon mode voltage in the output side, and the voltage cause damage to the application orsystem. For example, bearing current produced by common mode voltage does harm to motorbearing and lead to the premature of the ac motor; electromagnetic interference produced bythe high-speed switching power electronic devices inferences the running of other equipment;with the result of parasitic capacitance, the voltage transform into leakage current, whichcause pollution to the system even grid. What’s more, the amplitude of common mode voltagevoltage increase obviously with the increasing of voltage level, and it brings more serioushazard, so, it is very necessary to take action to reduce the damage by suppressing theamplitude of the common mode voltage.In the beginning of the paper, the development process of wind system is introduced, andit discusses the necessity of multilevel converter using in the wind power system. Then, theproduction mechanism and damage of common mode voltage is invested in variable speedconstant frequency double-fed wind power system. After the theory analysis of commonmode voltage, a novel SVPWM strategy is proposed for the five level neutral pointclamp/H-Bridge inverter and compared to some other strategies. The result of theory analysisand simulation are given to verify the feasibility and superiority of the novel SVPWMstrategy.The strategy suppresses common mode voltage effectively while the voltage utilization iskeeping more than90%of conventional SVPWM strategy, and it implement simply incascaded NPC/H-Bridge inverter.