A New PWM Voltage Source Inverter for Polar Coordinate Space Vector Control of AC Motors

This paper presents a new PWM voltage source inverter and an example of its applications. In this PWM inverter, the magnitude and frequency of the motor voltage are separately controlled. This inverter has the following special merits. 1) The arbitrary voltage space vector can be obtained in real time. 2) Compared with the conventional PWM method which synthesize the PWM pattern by comparing a sinusoidal reference signal with a triangular carrier, switching frequency of the switching elements (GTO) decreases to about two-third times. 3) The fundamental amplitude of output voltage is larger than that of conventional one. Moreover, the dead time error which distorts the voltage waveform is investigated in detail, and its compensation method fitted this inverter is given. As an example, this inverter is tested to drive a 2kW induction motor which is controlled by a vector control strategy based on the method of instantaneous symmetrical coordinates. As a results, a quick speed response (rising time is 6ms) and excellent characteristics are attained and it is verified that this inverter is suitable for variable speed drive of AC motors.