Comparison of Two Design Methods of EMI Filter for High Voltage Power Supply in DC-DC Converter of Electric Vehicle

In order to solve the problem that the conducted interference voltage of a high voltage/low voltage (HV/LV) DC-DC converter for vehicles exceeds the standard CISPR25-2016, two different design methods of EMI filter for HV power supply were proposed. The first method is to design a wide-band EMI filter at the high-voltage input port of the DC-DC converter. It can achieve the insertion loss of 60dB within 150kHz-108MHz. Another proposed method is to design a PCB-level EMI filter based on the resonance peaks suppression. During the PCB-level EMI filter design process, a high frequency equivalent circuit model of HV/LV DC-DC converter of EV considering the parasitic parameters was established, and by establishing the transfer functions at key frequencies of 200 kHz and 2 MHz, the dominated parameters responsible for the over-standard points were determined. From simulation and experiment results, the filters designed by above two methods can effectively reduce the conducted disturbance and comply with the limits requirements in 150kHz-108MHz. What's more, the PCB-level filter designed by the second method is smaller in size, only 1/5 of the filter size designed by the first method, lower in cost,and easy to be engineering.