The Currrent Loop Design Of Servo Driver

Current loop, as the inner ring of servo drive, its sampling precision, algorithm efficiency and response time are important for sinusoidal phase current, and directly affects the stability of the whole system. Based on the importance of the current loop, the subject mainly focus on the servo drive current loop design and analysis, considering the following points in the design process: 1) to achieve high-precision sampling when sampling current is large; 2) to reduce the inductance and flux impact on the system; 3) to optimize the performance of servo drives.It analyzes hardware and software of the current loop implementation in this paper. Hardware part includes current sampling circuit, encoder circuit and IPM peripheral circuit. Software part includes conversion of current module, calculation module of the real time rotate speed and electrical angle, the current regulator module, SVPWM realization and compensation technology module.et. Current sampling circuit module adopts single-phase current and two channel hardware circuit, conversion of current module gets current actual value through weighted values of the two-channel current. Small channel is responsible for accuracy, and big channel is responsible for measuring range, to achieve high accuracy and wide range of current sampling. Current regulator module adds feedforward control on the basis of the PI position regulator, to compensate electromotive force generated by inductance and electromagnetism, reducing the impact on the system. In compensation, bus voltage compensation restrains disturbance generated by voltage fluctuations; dead-zone compensation adopts phase compensation method to decrease dead-zone effect, achieving the improvement of system static property. High-precision current sampling design, PI + feedforward regulation algorithm and system property optimization ensure the better output of motor armature current and tracking feature, the better realization of the PMSM phase current control, building the foundation of speed and position loop’s digitized realization.In addition, fault handling for overcurrent, overvoltage and undervoltage is set in the current loop, protecting the system security. Currently, after project acceptance, servo drives achieve speed control, and the inspection results show that the design of the servodrive speed has small fluctuation, high control precision and stable operation, meeting the speed performance requirements.