EMI noise controlling methods suitable for electric vehicle drive systems

Methods to control EMI noises, especially common mode currents and radiations which are generated in electric vehicle (EV) drive systems, are studied in this paper. EMI noises, including common mode currents and near magnetic fields were measured using a prototype of the EV drive systems. FFT analyses of the voltage and current appearing in the EV drive systems showed that EMI noise sources are produced by voltage fluctuations occurring at the time of switching operations and the produced noise sources cause common mode currents to flow into the ground when the body frame is connected to the ground. Moreover, the flowing common mode currents induce radiated EMI noises while the generated EMI noises are transmitted between the inverter, batteries and motors; thus the produced radiated EMI noises have an effect on nearby vehicles. A method is proposed that controls common mode currents produced in EV drive systems so as to prevent a series resonance phenomenon from occurring in common current paths formed in EV drive systems. This technique is also effective in controlling radiated EMI noises. Furthermore, in order to control radiated EMI noises, a method is proposed that cancels the surface current flowing in P and N power transmission lines between the inverter and batteries. Effectiveness of these proposed EMI noise controlling methods was verified from simulations and experiments.