Research On Zero-position Correction And Torque Optimization Control For Drive Systems Of Permanent Magnet Synchronous Machines

The permanent magnet synchronous machine(PMSM)is widely used in industrial servo,rail transit and wind power generation due to its advantages of small size,high power density and high torque density.The high efficiency control of PMSM depends on the accurate rotor position information.However,high frequency mechanical vibration,complex electromagnetic signals and other interference factors will easily lead to faults in position sensors.Besides,it will also result the loss of initial rotor position due to the disassembling of motor,updating of controller software and hardware and other maintenance behaves.All of these will lead to the failure of accurately locating the position of rotor magnetic poles,and will further result in control system failure and even damages of equipments.To maximize the output efficiency of electromagnetic Torque,the maximum torque per ampere(MTPA)control strategy is usually adopted for convex pole permanent magnet synchronous machines.The main control objective of this strategy is to find the optimal stator current vector angle,and consequently,it is sensitive to rotor position error.The initial positioning error of the position sensor,the accumulated error during the operation process and the abrupt change in position information caused by the fault will lead to the inaccurate calculation of current vector angle,and will further result in a significant decrease in the torque output efficiency.When the motor runs under high power and heavy load,it may even face dangerous situations such as rotor blocking.Therefore,it is necessary to optimize the control system,to avoid the generation of rotor position errors,or to weaken the impact of errors,which can therefore improve the robustness and reliability of the system.Therefore,the main work of this thesis is divided into the following three parts:(1)The main solutions to obtain the rotor position information are investigated.Firstly,the advantages and disadvantages of existing acquisition methods for rotor position are summarized,including position sensored and sensorless algorithms.Then the working principles of incremental encoder and relevant zero correction method are studied.The zero correction of encoder installed on the motor shaft is carried out by the stator current vector method.Finally,the principle of sensorless algorithm is studied,including the sliding mode observer method,the high frequency pulse voltage injection method and the high frequency rotating voltage injection method.The simulation analysis of sliding mode observer based method is carried out at last.(2)The methods for zero correction of position sensor are investigated.On the basis of comparing and summarizing the existing methods,a new zero correction method based on the identification of intersecting axis flux is proposed.The proposed method includes two control modes.In mode 1,the rotor position is accurate enough through the controller without using the sensor position information,thus the zero offset angle is calculated.In mode 2,the zero offset angle is obtained online directly through the controller.Then,the feasibility and reliability of proposed method are verified by the zero correction test and the startup test with random initial position errors.The experimental results show that the two modes can effectively achieve the zero correction of position sensor,and have good accuracy in the correction of rotor speed and position,which can effectively make up for the shortcomings of existing methods to a certain extent.(3)The optimization of output torque under inaccurate rotor position information is studied.A torque optimization method based on the positionoffset flux linkage map is proposed for drive control system with inaccurate initial zero position information.In this method,the control current is recalculated by the position-offset flux linkage map,and the rotor position error will be corrected indirectly.Besides,a torque optimization method based on position error correction is proposed for working under Z-pulse fault of encoder.The direct correction of rotor position error is realized by using the flux linkage map under accurate rotor position.Both methods are verified by experiments and results show that the proposed method can effectively reduce the influence of rotor position error,and can properly solve the problem of efficiency decline under inaccurate rotor position,by which the purpose of torque optimization can be achieved afterwards.Overall,for the vector control system that uses sensors to detect rotor positions,this thesis proposes corresponding solutions to overcome the problem of control efficiency decline caused by position errors.The proposed zero correction method can avoid the error from the source,while the torque optimization method can effectively weaken the influence of position error in the control process.These methods can not only optimize the control efficiency,but also improve the robustness and reliability of the control system,and have practical values in engineering applications.