Abstract
In this article, a virtual cogging torque (VCT) control method to reduce the speed ripple of direct-drive permanent magnet synchronous machine servo system under low-speed conditions is proposed. Compared with other factors, at low speeds, the cogging torque is the main factor that deteriorates the drive performance, even induces speed oscillations. Especially in this article, due to volume limitation, the cogging torque is designed larger than normal one in order to remove the need of brake. Based on the model of permanent magnet synchronous motor, the cause and effect of the cogging torque are analyzed. Inspired by the characteristic of cogging torque, the VCT control method is proposed and investigated to significantly reduce the speed ripple at low speeds. The main idea of this proposed control method is to produce a proper VCT and continuously move the corresponding virtual stable equilibrium point to drive the rotor smoothly. In addition to the principle of this control method, its analysis and implementation are studied as well. Simulation and experimental results from the prototype demonstrate that the proposed control method is correct and valid, and it is simple and effective to smooth the speed at low-speed operations.
Highlights
SERVO system is an important system in many applications, such as industry, aerospace, etc
It can be seen from above simulation results that: (1) at low speeds, it is hard for the proportional integral (PI) control method and direct compensation control method to overcome the effect of large cogging torque in the target permanent magnet synchronous motor (PMSM), while the proposed control method can effectively reduce the speed ripple; (2) compared with high-speed conditions, under low-speed conditions, the effect of large cogging torque on the speed ripple is more serious, and even would cause creeping problem
This paper proposes the virtual cogging torque (VCT) control method for the speed control of direct-drive permanent magnet synchronous motor (DD-PMSM) servo system operating at low speeds
Summary
SERVO system is an important system in many applications, such as industry, aerospace, etc. Based on previous studies and the above problem, this paper proposes a novel speed-loop control method using the virtual cogging torque (VCT) to decrease the speed ripple of DD-PMSM servo system at low-speed operations. In this control method, a movable VCT is produced, and the speed loop is designed to continuously move the virtual stable equilibrium point (SEP) generated by the proper VCT at the reference speed so as to realize the speed control with the effective reduction of speed ripple.
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