Controller Design for Synchronous Reluctance Motor Drive Systems with Direct Torque Control

Abstract

The synchronous reluctance motor (SynRM) has many advantages over other ac motors. For example, its structure is simple and rugged. In addition, its rotor does not have any winding or magnetic material. Prior to twenty years ago, the SynRM was regarded as inferior to other types of ac motors due to its lower average torque and larger torque pulsation. Recently, many researchers have proposed several methods to improve the performance of the motor and drive system [1]-[3]. In fact, the SynRM has been shown to be suitable for ac drive systems for several reasons. For example, it is not necessary to compute the slip of the SynRM as it is with the induction motor. As a result, there is no parameter sensitivity problem. In addition, it does not require any permanent magnetic material as the permanent synchronous motor does. The sensorless drive is becoming more and more popular for synchronous reluctance motors. The major reason is that the sensorless drive can save space and reduce cost. Generally speaking, there are two major methods to achieve a sensorless drive system: vector control and direct torque control. Although most researchers focus on vector control for a sensorless synchronous reluctance drive [4]-[12], direct torque control is simpler. By using direct torque control, the plane of the voltage vectors is divided into six or twelve sectors. Then, an optimal switching strategy is defined for each sector. The purpose of the direct torque control is to restrict the torque error and the stator flux error within given hysteresis bands. After executing hysteresis control, a switching pattern is selected to generate the required torque and flux of the motor. A closed-loop drive system is thus obtained. Although many papers discuss the direct torque control of induction motors [13]-[15], only a few papers study the direct torque control for synchronous reluctance motors. For example, Consoli et al. proposed a sensorless torque control for synchronous reluctance motor drives [16]. In this published paper, however, only a PI controller was used. As a result, the transient responses and load disturbance responses were not satisfactory. To solve the problem, in this chapter, an adaptive backstepping controller and a model-reference adaptive controller are proposed for a SynRM direct torque control system. By using the