Stability Analysis of FPGA-Based Control of Brushless DC Motors and Generators using Digital PWM Technique

Brushless dc (BLDC) drives have received significant attention, owing to their high efficiency, electromagnetic interference, and high mechanical reliability due to the absence of brushes in commercial, residential, and industrial applications. In generating mode, they are very suitable for small wind and hydro generator applications, as well as integrated starter alternators in hybrid electric vehicles. This paper discusses digital pulsewidth modulation control for a BLDC drive in both motoring and generating modes of operation. This control strategy is simple and robust, requires no current sensors, and is not computationally intensive. Owing to these attributes, the technique can be implemented on a low-cost field-programmable gate array. This paper investigates potential stability issues due to the simplicity of this control under various conditions of load disturbances and also owing to the reduction in processor capability. Lyapunov stability criteria have been used to analyze the closed-loop stability of the system. Furthermore, an approximate discrete model has been developed, and the stability of the system is analyzed to ensure closed-loop operation under various sets of loads, speeds, and input voltages. Simulation and experimental results have been presented to verify the claims.