A Cancellation-Based Circuit for Reducing Both the Shaft Voltage and CM Noise in Motor Drive Systems

In motor drive systems, the common-mode (CM) voltage of the inverter introduces negative impacts such as the shaft voltage and CM noise. The shaft voltage generates bearing current and may reduce the lifetime of bearings, while the CM noise may interfere the operation of the nearby equipment. With the wide application of silicon-carbide (SiC) MOSFETs, these negative impacts are aggravated since higher d<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v</i>/d<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> is generated. In this article, a cancellation-based circuit is proposed for reducing the shaft voltage and CM noise in motor drive systems simultaneously. To determine the key parameters of the circuit, a double voltage test (DVT) is proposed, avoiding complex procedure of extracting parasitics in the motor. Compared with existing methods, neither active devices nor magnetic components in the power stage are required, achieving low volume and low cost. By analyzing the effect of parasitics, the effective frequency range for the cancellation-based circuit is derived. Finally, a motor drive system is built in the lab, and the proposed method is tested to verify the effectiveness of the cancellation-based circuit.