Impact of Zero-Volt Loop Control on Efficiency of Switched Reluctance Motors

Zero-volt loop (ZVL) algorithms are known to be able to reduce peak flux linkages and resulting iron losses while keeping the same average torque in average torque control (ATC) of switched reluctance motors (SRMs). However, exploiting ZVLs to minimize the losses has been challenging due to the strongly nonlinear correlations between the torque and the control parameters of ATC caused by extensive magnetic saturation. In this paper, a fast optimization method for loss minimization is proposed, which can utilize all control parameters of ATC while operating with ZVL control. The proposed optimization method quickly calculates the current reference, which is one of the control parameters, so as to satisfy a torque reference, and consequently removes the time-consuming nonlinear constraint on the torque from conventional optimization methods. Using the proposed optimization method, the impact of ZVL control in loss minimization of SRMs is investigated with detailed simulations and experiments. The results verified that the utilization of ZVLs reduces iron losses without significantly increasing copper losses. It was found that the loss reduction was especially large (more than 15%) at medium speed and partial load. The loss reduction in the Japanese JC08 driving cycle for automotive propulsion for city driving was investigated and was as large as 15%. Furthermore, the vibrations that cause acoustic noise were also reduced.