A motor speed control system using dual-loop PLL and speed feed-forward/back

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 has slow rising up characteristics than speed feed-back, and cannot avoid over/undershoots. Nonetheless, the first loop has rapid rising up characteristics and 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 speed feed-forward/back. It has fast rising up characteristics and no over/undershoots thanks to the first and third PLL as F/V converter, which cannot be achieved in traditional PLL systems.