Performance Improvement in Microprocessor-Based Digital PLL Speed Control System

A microprocessor-based digital PLL speed control system for motor drives is discussed on its load characteristics, stability, and speed control accuracy. The digital and hybrid simulations as well as the Z transform are used to analyze these items of discussion. As the results of the analysis, two compensating methods, that is, the current compensator and the speed feedback loop are proposed for enlargement of both static and dynamic operating load torque ranges of the PLL-controlled motor. This effect of the compensators is predicted through theoretical procedures, assessed by the hybrid simulator, and confirmed by experiments. The effects due to the current compensator and the speed feedback loop on the stability and the speed control accuracy of the PLL system are inspected with the aid of digital and hybrid simulations. These compensators do not virtually affect the stability of the PLL system. The speed control accuracy of the PLL system can be increased by virtue of the speed feedback loop. Design examples based on the discussion in this paper are provided and the authors conclude that the methods for performance improvement have substantial effects on the practical design for the microprocessor-based digital PLL speed control system.