The Study Of Pmsm Positioning Control Based On Sliding Mode Variable Structure

The position control of motors is different from start and speed regulating control. It is a special form of servo motion, which requires higher positioning accuracy and dynamic response performance. The high inertia load is widely used in many fields. For example, daily life, industry, construction, aerospace, military, etc. Because of lager moment of inertia than normal load, the responds of the motion control system is lagging seriously. With high inertia load, it is more difficult to control the exact position of the controlled object in real time in practical applications.In this thesis, the Sliding Mode Control(SMC) theory and the advantages of various sliding surfaces and reaching laws are descripted briefly. By changing various variable parameters in SMC, the impact of control system was obtained. Since the actual load torque is unmeasurable directly, a PMSM load torque observer was designed on the reduced order state observer theory, and got its discrete form. The stepping control theory has been analyzed, and simulated the inching movement of it.With the traditional three-speed positioning control difficult to achieve high positioning accuracy and time requirements under high inertia load, the method of SMC with stronger robustness was used to optimize original control strategy. The motor positioning SMC controller is designed based on SMC theory. The Step-motion Control was still adopted in rise and constant speed stage. In the slowdown stage, the current phase angle was controlled by Step-motion Control and the current amplitude was regulated by SMC. The fast and accurate positioning under high speed of PMSM has been achieved. The cases of current phase and amplitude as the output SMC control variable were modelled and simulated and compared the results.For the problems of exceeding the speed limit by SMC in longer orientation distances and large torque ripple in rise and constant speed stage of three-speed positioning control method after optimization, the strategy of phase and amplitude of current vector control coordinately by stages is put forward to improve torque characteristics. The different control variables were gotten combined with the piecewise SMC theory. Simulation and experiments confirmed the effectiveness of this control strategy to improve the PMSM positioning precision and robustness.