A motor speed control system using a hybrid of dual-loop PLL and feed-forward

Abstract

PLL speed control systems can completely reject speed error and steady-state phase error for constant-speed inputs. Though it does not usually handle inputs including acceleration, the dual-loop scheme improves, as a feed-forward control system, rising time and phase error for acceleration input. However, since it is fundamentally a third-order PLL, it cannot avoid over/undershoots when gain is set high for fast responses. Nonetheless, the first loop has no over/undershoot, since it is an ideal second-order PLL system. In this article, to solve the problem, we show a hybrid system of the dual-loop PLL and feed-forward. It has no overshoot thanks to the rising up characteristics of the first PLL, which cannot be achieved in traditional PLL systems.