A Motor CM Impedance Based Transformerless Active EMI Filter for DC Side Common-Mode EMI Suppression in Motor Drive System

Due to the continuous switching action of the inverter in the motor drive system, an electromagnetic interference (EMI) is generated in the system. Active EMI filter has a smaller volume and higher power density compared with the widely used passive EMI filter. However, for the conventional voltage-sensing voltage-compensating active filter and the current-sensing current-compensating active EMI filter, the active EMI filter itself needs a transformer to compensate or to sense the EMI noise and this will increase the volume of the active EMI filter. In order to save the sensing or the compensating transformer required by the active EMI filter itself, a voltage-sensing current-compensating active EMI filter for the motor drive system is designed. Combining the sensed common-mode (CM) voltage with the artificially fitted ac-side CM impedance network, the adverse CM current can be generated that can be used to suppress the dc-side CM EMI. This active EMI filter itself does not need any transformer in principle. Experimental results have validated the effectiveness of the proposed active EMI filter. It is shown that using this active EMI filter can simplify the structure of the active EMI filter and effectively suppress the dc-side EMI.