Performance and stability analysis of an AC variable speed drive

Abstract

In this dissertation an experimental, speed sensorless, AC variable speed drive is developed from works presented by previous researchers and the performance and stability of the drive is analysed. The experimental drive consists of a simple control algorithm that can be implemented on low cost systems and provides a performance that is superior to standard constant V/f drives. There has been a great deal of research into AC variable speed drives and many different speed control schemes have been developed which range in complexity, performance and cost. Open-loop scalar control techniques are generally the least expensive to implement as no motor speed sensor is required. These techniques are likely to prevail in applications where instantaneous speed and position control of induction motors is not critical. Such applications may include pumps, fans and conveyors. The experimental drive analysed in this dissertation is an open loop scalar control scheme. It utilises field orientation to control the stator voltage in the synchronously rotating frame and employs constant V/f control for basic voltage regulation. Compensation for stator resistance voltage drop and rotor slip are also employed to improve the dynamic performance and to reduce the steady state speed error.