This paper presents a performance analysis of a four-leg inverter (FLI) in driving two motors with vector control. We show that an expanded two-arm modulation (ETAM) known as a modulation method of a five-leg inverter is applicable for the four-leg inverter and we theoretically analyze a performance analysis of the four-leg inverter in driving two motors with vector control. (c) 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.