Digital control of PM brushless DC machines in generating mode

A significant increase in distributed generating system technologies in the past decade has stimulated the development of electrical drives with brushless DC machines (BLDC). Conventional control of such drives is mainly examined and well known for applications where BLDC is working in motoring mode. BLDC drives are widely used due to their high efficiency, high power density, simple construction and low maintenance. With advancements in power electronics, the control of BLDC machines becomes more flexible for variety of applications. However, control of BLDC drives in generating mode and four-quadrant operation has not been examined thoroughly despite the fact that such machines have very high power density and field weakening capability compared to other electrical machines (brushed DC as well as asynchronous and synchronous machines). Furthermore, the main challenge in generating mode applications is to keep a wide operating range for variable shaft speeds. Conventional control algorithms that are used to control BLDC drives in generating mode have complex control routines and are not fault tolerant. As a result, control hardware of variable speed generators is quite complex and costly.;This dissertation shows the fundamentals of BLDC drives, operating principles, conventional control and dynamic operations. It also proposes a novel digital control concept for BLDC drives, as a trouble-free control principle, explaining the theory behind it and its simple implementation. Two different digital control approaches are presented: hysteresis and pulse-width modulation (PWM). In addition, an adaptive control algorithm is introduced, which increases the reliability of the system and enables fault tolerant operation for a wide speed range. Such adaptive strategy adjusts the control parameters to the load; therefore, for each load variation, it modifies its parameters in order to the find optimum operating point. This results in a broader operating range of the machine, using a simple and easy to implement control strategy. The direct benefit is that such control strategy can either be part of an existing algorithm or can be implemented in FPGA. Target applications for digital control of BLDC drives include propulsion systems, wind turbines, hydro turbines and aerospace and naval systems.