A PWM motor speed control system based on the dual-loop PLL

PLL motor speed control systems can completely reject speed error and steady-state phase error for constant-speed input signals. However, it is not usually applied to systems with inputs including acceleration, because they have poor tracking speed and strange pull-in behavior. In the field of radio communication, "dual-loop PLL" is very effective for such signals. It can not only enable high-speed tracking, but also cancel phase error. This article shows that the principle can be applied, with some devices, to motor speed control, and a prototype implementation using PWM is described. Two supplemental techniques, called "active feedforward" and "active limiter", are also incorporated, to achieve faster tracking and speed limitation. The scheme was implemented by programming an FPGA, and satisfiable results were obtained.