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This paper focuses on the high-frequency leakage current flowing through the grounded heat sink of a voltage-source PWM inverter in an adjustable-speed motor drive system. A passive EMI filter is proposed, designed and tested for a 200-V 3.7-kW adjustable-speed motor drive system. This filter is unique in the sense that it requires access to the ungrounded motor neutral point. An equivalent common-mode circuit for the motor drive system equipped with the EMI filter is derived from experimental waveforms along with theoretical discussions. Experimental results verify that the passive EMI filter is viable and effective in eliminating both heat-sink and motor-frame leakage currents from the motor drive system.