Optimization-Based Duty Cycle Allocation for a Five-Leg Inverter to Drive Two Electric Motors

Abstract

Driving two electric motors with a five-leg voltage source inverter (FL-VSI) by connecting one phase of each motor to a common leg possesses the advantage of reducing the number of power switches. This article proposes a duty cycle allocation method to make FL-VSI use the DC bus voltage more efficiently. In this method, the motor with a smaller common leg duty cycle requirement is set as the first priority. An additional period of duty cycle is added simultaneously to the first-priority motor's three phases to compensate for the difference of the common leg duty cycle requirement between the two motors. Thereby, the duty cycles of the three legs connecting to the first-priority motor, including the common leg, are confirmed. Then, the duty cycles of the remaining two legs connecting to the second-priority motor are allocated by solving a nonlinear optimization problem. The objective of the optimization is to make the inverter output voltage close to the voltage requirement of the second-priority motor. Experiments have been implemented, and the results verify the improvement of the proposed method.