Research On Control Techniques Of High Performance AC Servo Drive For Numerical Control Machines

This dissertation focus on high-performance servo drive for feeding of NC(Numerical Control) machines. PMSM and SVPWM technique are applied into almost all the modern NC machines. Due to the high-performance demand of NC machines, the feeding mechanism, PMSM, SVPWM-based inverter and disturbances are deeply analyed. The range of application for mathematical assumes in high-performance servo drive is studied. Influences of torque ripple caused by PWM and coupling between Iq and Id are selectively analysis. Parameter differences among difference axis will cause bad machining effect, especially when couplling existing through workpieces. Researches on mathematical model and descriptions of NC machine feeding servo drives are carried out.The principle of SVPWM inverter work principle is further analyed and studied. Inverter is the basis of SVPWM. PWM is achieved by a certain frequency carrier. Every sine wave is composed of some pulses. Harmonics are caused by this approach inevitablely, especially in low speed section; torque and speed ripples are generated, which deteriorate machining performance. The effect of carrier frequency is analyed. Based on this, the switching characters and carrier frequency control methods are studied.AC drive systems based on SVPWM is deeply analyed. The basis of vector control is the decoupling between Iq and Id, while AC servo motor is a close coupling object. At the same time, some nonlinearities and time-variable factors exist. Based on the analysis, coupling between Id and Iq and decoupling methods are studied in this dissertation. Adaptive control strategies are studied aiming at the time-variable character of the servo motor.As a kind of typical control system, servo system has high performance demanding on stability, rapidity and precision. The feeding axis of NC machines are coupled through workpieces. Exactly coordinating multi-axis is needed during the high-performance machining process. Hence, besides the excellent characters of the system itself, consistency must be kept. During the machining process, initia variation with workpieces, different disturbances on every axis, and the coupling between Z-axis and the others axis on and off, all this set handicaps for system designing. Adaptive control principle-based speed controller and compensator are studied based on the disturbances analysis. To validate the effect of analysis and simulation results and accomplish the Enterprise-College-Research(ECR) cooperation project, real servo drives are made based on the analysis and simulations. The XKHL650 vertical machining centre(VMC) with the drives are setup as the test bench. All the control strategies are validated on this bench. At last, three typical workpieces are machined by this VMC. The experiments and part of experiment results are shown in this dissertation.