文档介绍：英文资料
The contral techniques drives and contrals handbook
Chapter A4
Torque, speed and position control
General principles
The ideal control system
Many applications exist where something has to be controlled to follow a reference quantity. For example, the speed of a large motor may be set from a low-power control signal. This can be achieved using a variable-speed drive as described in the following.
Ideally, the relationship between the reference and the motor speed should be linear, and the speed should change instantly with changes in the reference. Any control system can be represented as in Figure , with an input reference signal, a transfer function F and an output. For the system to be ideal, the transfer function F would be a simple constant, so that the output would be proportional to the reference with no delay.
Figure Variable-speed drive and motor
Open-loop control
Unfortunately, the transfer function of many practical systems is not a constant, and so without any form of feedback from the output to correct for the non-ideal nature of the transfer function, the output does not follow the demand as required. Using an induction motor supplied bya simple open-loop variable-speed drive as an example, the following illustrates some unwanted effects that can occur in practical systems:
Speed regulation. The output of a simple open