Abstract
Inverter-driven synchronous motors are widely used in high-performance variable speed drive systems used for electric vehicles. The armature current vector of synchronous motors is decided according to the command (torque or speed) and the current-regulated voltage source pulse width modulated (PWM) inverter drives synchronous machine so that the instantaneous armature currents follow their commanded values. The stator and winding of synchronous machines are the same as standard induction motor, but the rotor configuration is different depending on the type of machine. Therefore, synchronous motor with permanent magnets can be modeled by the same d-q reference frame circuit and generally analyzed, where the machine parameters in the d-q equivalent circuit depend on the rotor configuration. The current vector of synchronous machines driven by the current-regulated PWM inverter is controllable, and as a result many useful control algorithms of the current vector have been proposed in order to improve the operating characteristics. The maximum torque per ampere control is useful for predicting the maximum torque considering the current constraint. In this article, the effects of machine parameters and the operating characteristics, such as the maximum torque in the constant torque region, with respect to several types of synchronous motors are examined.The optimum current vector producing the maximum output power at any speed is derived considering both current and voltage constraints.The selection of machine parameters and design are discussed in order to obtain the desired output characteristics.