Nonlinear control of a synchronous reluctance drive system with reduced switching frequency

A novel PWM switching method and control algorithm for synchronous reluctance drive systems is proposed. First, in different switching modes, the current slope of the stator current can be systematically derived. The current slope is related to the dc-bus voltage, operating conditions, and parameters of the motor. Then, by computing the derivation of the current slope command and the real current slope, an optimum switching state can be determined and used to trigger the inverter. After that, the nonlinear controllers for an adjustable speed drive system and a position control system are proposed. Using the proposed method, the synchronous reluctance drive system performs very well. It has smaller current harmonics, lower switching frequency, and less switching loss when compared to the hysteretic or bang-bang current control. In addition, a fast transient response, good load disturbance rejection ability, and good tracking performance of speed control and position control can be achieved. No extra hardware is required. Several experimental results validate the theoretical analysis.