Research And Implementation Of EMI Passive Filter In Motor System

The electromagnetic interference (EMI) affects the reliable operation of motor system. This problem should be solved with effective measures. Particularly, using the passive filter is the most effective measure. So EMI passive filter of motor system is composed by mains filter and output side filter.While designing the mains filter, separating EMI into common mode (CM) and differential mode (DM) component is the problem which is should be solved firstly, and also is the difficulty point. The CM spectrum is separated from the interference signal which is measured by LISN in the power supply by DM rejection network composed of three precision resistors. The DM spectrum is calculated with the definition of CM and DM. By the separate results, and the GB4343.1-2003, design the CM and DM circuits of the mains filter. In order to solve the impedances mismatch of mains filter, using the S parameter of the mains filter's port network, based on the source impedance and the load impedance in actual system, the insertion loss of any operation circumstance can be obtained by calculation. While designing the output side filter, using the common mode equivalent circuit of motor's coupling parameter, the shaft voltage is reduced to less than the breakdown potential of lubricant film in order to prevent the shaft current. This output side filter takes the motor winding's inductance and coupling capacitance into consideration, so that the volume and cost are reduced. At the same time, the feedback element is used to deliver the CM current in the motor terminal to the input port of the output side filter. This technique improves the filter's performance in the aspect of suppressing the shaft voltage.The main reason that affects the filter's high frequency performance is the passive device's parasitic parameter and the coupling between them. So that measure should be applied to improve the filter. This dissertation applies PCB plane winding, making use of the negative coupling to suppress the capacitance's parasitic induction. In order to solve the problem of coupling effect, network analysis method is used to get coupling parameter. Change the winding's structure and shield the capacitance to reduce the coupling between passive devices. Comparison of experimental results verify that after applying the measure to the system, the high frequency performance of EMI filter is improved greatly, and also verify the availability of the adopted measure.Based on the EMI passive filter's design principle and method in motor system, as well as the system improvement measure mentioned above, we can design the EMI passive filter which is applied in motor system and can suppress the electromagnetic interference's disadvantages effectively.