A Method for Improving Hysteresis Motor Torque Characteristics Based on Harmonic Injection

Hysteresis motors are widely used in chemical, food, and medical industries owing to their contamination-free operation and high reliability. However, the insufficient torque and low efficiency remain critical challenges, while prior solutions often require complex structural modifications, limiting practical applicability. To address this gap, this article proposes a torque improvement method just by injecting current harmonics through the control program. First, a coupled field-circuit analytical model is established, incorporating current and magnetic field harmonics based on material tests. Then, the optimal harmonic components are determined via Lagrange multiplier optimization, minimizing copper loss while maintaining target torque. Finally, simulations and experiments (including asynchronous and pull-out tests) validate the method’s effectiveness. By injecting third-order harmonic, the hysteresis torque can be increased by 15% under the same current condition, or the input power can be reduced to 85% under the same torque, thereby improving the practicality of hysteresis motors.