An Auxiliary Circuit for Improving Torque Per Ampere of Switched Reluctance Machines

Switched reluctance motors are one of the potential candidate to challenge the popularity of BLDC/PMSM motors in the EV and aerospace applications due to absence of rare earth magnetic elements. One of the major limitation of switched reluctance machines (SRMs) as compared to the BLDC motors is the lower value of torque per ampere (TPA). TPA is lower because positive torque cannot be obtained at all positions of the rotor (θ) around the stator but only for a limited range of values of θ. The challenge is to utilize the torque producing values of θ to the maximum extent. In this paper, a technique to enhance the value of TPA is proposed using an auxiliary converter to maximize the utilization of torque production region in a rotational cycle. The proposed auxiliary converter applies a voltage in series with the main converter voltage to increase the rate of rise and fall of current to effectively utilize the torque producing capability of the machine. This helps to obtain the same torque using low value of current, thereby increasing TPA and reducing the conduction loss. The proposed technique is validated using simulations and is found to increase the motor torque for a particular current reference by 22%. Some of the results are presented here.