中英文翻译直流电机的闭环控制和微机接口大学学位论文.doc

Closed-loop control of DC drives AND Microcomputer Interface A basic scheme of the Closed-loop speed control system employing current limit control ,also know as parallel current, is shown in fig 4-2A-1. Fig 4-2A-1 driver with current limit control Wn* sets the speed reference. A signal proportional to the motor speed is obtained from the speed sensor. The speed sensor output is filtered to remove the ac ripple and compared with the speed reference .the speed error is processed through a speed controller. The output of the speed controller Uc adjusts the rectifier firing angle α to make the actual speed close to reference speed. the speed controller is usually a PI(proportional and integral) controller and serves three purposes-----stabilizes the drive and adjusts the damping ratio at the desired value ,makes the steady-error close to zero by integral action, and filters out noise again due to the integral action. The drive employs current limit control, the purpose of which is to prevent the current from exceeding safe values .As long as IAIx, where Ix is the maximum permissible value of IA, the current control loop does not affect the drive operation. If IA exceeds Ix, even by a small amount, a large output signal is produced by the threshold circuit, the current control overrides the speed control, and the speed error is corrected essentially at a constant current equal to the maximum permissible value. When the speed reaches close to the desired value, IA falls below Ix, the current control goes out of action and speed control takes over. Thus in this scheme, at any given time the operation of the drives is mainly controlled either by the speed control loop or the current control loop, and hence it is also called parallel current control. Another scheme of closed-loop speed control is shown in Fig.4-2A-2. Fig 4-2A-2 driver with inner current control loop It employs an inner current control loop within an outer speed loop. The output of the