Improvement of Motor side converter voltage using Common Mode filter at the grid side converter in a grid connected Motor Drive system

Common Mode (CM) noise produced by modern high-frequency PWM converters needs special attention to handle. The problem with the CM noise is that it flows through the parasitic elements, which makes the design of the CM filter more challenging, without accurate knowledge of the parasitic components. This paper presents a passive filter topology, which improves the motor terminal voltage without using a dedicated CM choke. The topology minimizes the effect of parasitic capacitance up to several MHz and allows the reduction of the CM inductor. Additionally, it is also shown that with detailed mathematical modeling, the design of the passive filter can be done with the aid of a computer program. Wide Band Gap (WBG) device technology will allow higher switching frequencies for the converter to help reduction of the passive filter volume and cost. The switching frequency need to be part of the optimization routine which will result in customized passive filter for converters with different applications. The passive filter design needs to be automatic, to obtain quick results for a new design effortlessly. A detailed analysis and hardware verification of the proposed filter and the modeling method are presented in this paper. NPC 3 level, SiC (Silicon Carbide) MOSFET modules from Microsemi are used in the converter construction and the chosen switching frequency is 48 kHz. An RL load is used in place of the motor for simplicity.