Contents I. Introduction
Compared with direct current motor for speed control, synchronous motor has more advantages, such as large unit capacity, light weight, small volume, small floor area, small rotational inertia and good dynamic response. And compared with asynchronous motor, it has high power factor, small frequency inverter capacity, small motor size and rotational inertia, and high control precision etc. Just because it has so many above advantages, synchronous motor has been used successively in adjustable-speed AC drive system in home and abroad industrial circles. Direct Torque Control is a new high-performance control technology of adjustable-speed AC drive which developed after vector control technology. It can get the high dynamic performance of torque. At present, the DTC technology has been a new focus in research field of AC drive. The direct torque control strategy is often studied in asynchronous motor and permanent magnet synchronous motor, but seldom in salient pole synchronous motor. Although salient pole synchronous motor and permanent magnet synchronous motor both belong to category of synchronous motor, the rotor of former has excitation winding and damping winding. This makes salient pole synchronous motor different from permanent magnet synchronous on regulation mechanism. So it is very necessary to further study the direct torque control of salient pole synchronous motor.
