Pulsewidth Modulation Techniques for Low Cost Voltage Source Inverter Applications

Abstract

Optimized PWM techniques have been developed and used with good results for voltage source inverters. However, implementation frequently requires complex electronic circuits, usually microprocessor-based, that cannot be justified in low cost applications. The paper examines three phase PWM pattern generators that are simple to implement with low cost circuitry, particularly with analog components. These modulation techniques are based on the model reference adaptive (MRA) technique. They exhibit intrinsic constant Volts/Hertz operation, and do not require frequency synchronization and frequency jumping, making them ideal for low cost inverter driven variable speed ac motor drives. The PWM patterns are generated by forcing the current in the built-in load model to follow a reference, by means of hysteresis control, also known as the delta modulation technique, or error triangulation control. Unlike delta modulation, the latter technique exhibits constant switching frequency and has an output voltage spectrum similar to that of the well-known sine PWM technique. The paper includes the principles of operation, the control circuit structure and implementation and the features of the PWM patterns.