Novel Sliding Mode Speed Control For Permanent Magnet Synchronous Motor With A Speed And Load Torque Observer

In recent years, with its high power density, high efficiency and simple structure,permanent magnet synchronous motor (PMSM) has been extensively utilized inaircrafts, robots, electric vehicles, home appliances, etc. In practical applications,PMSM systems are always confronted with various uncertainties that may begenerated internally, e.g., parameter perturbation, friction force and unmodeleddynamics, or externally, e.g., load torque disturbance. As a result, it is very difficultfor linear control schemes, such as PI control, to achieve high accuracy, highreliability and strong disturbance rejection ability performance. Therefore, advancedcontrol methods can become an alternative solution to accurately track the referencetrajectory of PMSM. In this paper, a novel sliding mode variable structure controlstrategy is proposed to achieve fast dynamic response and robustness of PMSM.The mathematical models of PMSM in different coordinate systems areintroduced, and the sliding mode variable structure control theory is studied. Thispaper sorts out the causes of chattering problems followed by its suppressionstrategies, and analyzes the design process of a sliding mode controller based on theconventional reaching law. A new speed control strategy consisting of a sliding modespeed controller (SMSC) based on a novel reaching law, and an extended observer isproposed for a PMSM. The reaching law contains an exponential item of slidingsurface and speed error. By mathematical deduction and discrete analysis, slidingbandwidth and reaching time are deduced, which proves that the proposed reachinglaw is able to deal with the chattering and reaching time problems existing inconventional reaching law. A SMSC based on this reaching law is built for PMSMsystem. Simulation results show that the sliding mode controller can obtain satisfyingperformance with strong robustness. Furthermore, an extended sliding mode observer(SMO) is designed to estimate rotor speed and load torque. The Lyapunov stabilitytheory proves that the designed observer is existed and stabilized followed bychattering reduction method and robustness analysis. The speed observation avoidsthe measurement noise and discretization error caused by differential calculationmethod. And the load torque is considered as a feedforward part to the SMSC toimprove the disturbance rejection performance and to further reduce chattering of the SMSC.Thus, a novel sliding mode control strategy is formed composing with a slidingmode controller and an extended SMO. An experimental setup is built based on thetheoretical analysis and simulation results to implement the proposed sliding modecontrol strategy. The experimental results show that the proposed strategy canguarantee better performance with fast dynamic response, reduced chattering, strongrobustness and disturbance rejection ability.