Servo drive is an important part of modern motion control, which is widely used in industrial robots and CNC machining centers and other automation equipment. In particular, servo drives used to control AC permanent magnet synchronous motors have become a research hotspot at home and abroad. At present, the three-loop control algorithm of current, speed and position based on vector control is generally adopted in the design of AC servo drives. Whether the speed closed-loop design is reasonable or not plays a key role in the entire servo control system, especially the speed control performance.
In the speed closed-loop of servo drives, the real-time speed measurement accuracy of the motor rotor is essential to improve the dynamic and static characteristics of the speed loop for speed control. In order to find a balance between measurement accuracy and system cost, incremental photoelectric encoder is generally used as the speed measurement sensor, and the corresponding common speed measurement method is M/T speed measurement method. Although the M/T velocimetry method has a certain measurement accuracy and a wide measurement range, this method has its inherent defects, mainly including: 1) at least one complete code disc pulse must be detected in the speed measurement cycle, which limits the minimum measurable speed; 2) the two control system timer switches used for speed measurement are difficult to keep strictly synchronized, and the speed measurement accuracy cannot be guaranteed in the measurement occasion with large speed changes. Therefore, it is difficult to improve the speed following and control performance of servo drives in the traditional speed loop design scheme using this speed measurement method.