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