The Speed Loop Design Of Servo Driver

The speed loop design plays an important role in a servo driver. Considering the following points in the design of speed loop: Firstly, sudden speed changes will make attack on the system. Secondly, when the motor load changes suddenly, the system under load will not response timely and anti-interference capability will be reduced. Thirdly, if the resonance phenomenon of mechanical structure occurs when the motor is running or the tremble occurs when the motor is shutdown, the availability of the system will be reduced.Based on above considerations, in this work, we address the design of the speed loop in a servo driver, which consists of S-type smoother, current speed measurement, the PDFF control of the speed loop, and the vibration suppression. An S-type smoother processes a given speed command smoothly and reduces the impact, caused by speed changes, on the system. The current speed is measured by permanent magnet synchronous motor(PMSM) with an incremental encoder. In order to make the current speed smoother and change more slowly, the measured value is filtering processed. The PDFF control of the speed loop is based on the position type PI control algorithm with a feedforward and is used to increase the response and anti-interference capability of the system under load. The vibration suppression is considered as two states: Firstly, it aims to inhibit the resonance suppression of mechanical structure, without changing the control gain parameters, which includes the resonance suppression low-pass filter and resonance suppression notch filter. Secondly, the tremble occurring in motor’s shutdown is suppressed.In addition, the over speed is set and the encoder abnormal is dealt with in the speed loop. This designed servo driver is able to control the speed of the motor through acceptance. Furthermore, the test results show that the rate of speed error and fluctuation is little and the speed loop works well, meeting the requirement.