New methods to suppress EMI noises produced in the motor drive system

A method is studied which suppresses common mode currents flowing in a motor drive system. The method is based on the analyses of EMI noises at high frequencies. EMI noises are analyzed using the FFT method, and separating the motor drive system into three parts: the source (ACL) side, the power converter side and the load (motor) side. It is found through these analyses that there are four resonance frequency components having a strong influence on common mode currents appearing in the motor drive system. Three components of them are generated in power converters (rectifier and inverter); i.e. the two resonance components are produced by switching operations of power converters, and the third component is produced by DC voltage fluctuations superposing on P (or N)- power transmission lines of the converter (rectifier) and inverter. The fourth one is produced by a micro-surge occurring at the terminals of the motor. A method is proposed that controls these resonance components, separating the motor drive system into the three sides. The effectiveness of the proposed method is verified through simulations and experiments.