Research on a High Frequency Active EMI Filter for Power Converters

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This research is concerned to a high frequency active noise filter of electromagnetic interference (EMI) composed of active devices as transistors and a high frequency common mode current transformer(CT).The merits of this filter and the results obtained in this research are as follows ;1. Small size under 1 / 10 of volume and weight is obtained.2. Under 2% of the common mode current compared to the normal operation is realized. The result means the reduction of the common mode noise and leakage current.3. The common mode EMI noise can be reduced 35dB under the area of 3MHz. The active filter fits for low frequency area EMI filter under 1MHz. So combining a high frequency passive EMI filter upper 5MHz area, small size and high quality EMI filters can be realized.4. The filter is composed of a small ferrite CT and two complimentary transistors and a DC cut capacitor. Therefore, it can produce very economical price as under 1$.5. It needs no separate power source by feeding the power from DC link of the inverter.6. Low loss under 1W in 2kW PWM drive system is realized.7. The mechanism and the equivalent circuit of the leakage current of the inverter motor drive systems are cleared. Using the results, dv/dt of the inverrers and motor stray capacitance can be designed by simulation.8. The developed EMI active filter is already applied to industrial inverters and home air conditioner drive systems.