Direct Torque And Direct Suspension Force Control Of Bearingless Permanent Magnetsynchronous Motor

A bearingless permanent magnet synchronous motor(BPMSM) is a kind of bearingless motor with excellent performance,which has realized bearingless technology on the basis of a permanent magnet synchronous motor.It succeeds some excellent performances of permanent magnet synchronous motor,such as great power density,high power factor and high efficiency,and has the magnetic bearings’ excellent characteristics,such as no mechanical friction,needless lubrication, no pollution,long life-span and little maintenance.It can operate under high speed or hypervelocity,and has potential prospects for applications in the hi-tech fields of chemistry & chemical engineering,life sciences,energy transportation,aerospace,robot,etc.There are two kinds of control methods for traditional permanent magnet synchronous motors,namely vector control and direct torque control(DTC).Compared with the vector control,the DTC has many advantages,such as simple control structure,fast response speed,good static and dynamic performance,and strong robustness for motor’s parameters.Traditional radial suspension forces of the BPMSM are controlled with the rotor magnetic orientated method,which relies on motor’s parameters too much,and it’s difficult to achieve the theoretical results due to the complexity of vector coordinates transformation;an open-loop control is adopted to control suspension force, which affects the accuracy and dynamic response performance of suspension force control; traditional suspension force vector control adopts current following inverter,which have high switch frequency;the utilization rate of inverter capacity is relatively lower.This thesis is sponsored by the National High Technology Research and Development of China(863 Program),and focuses mainly on the mathematic models of BPMSM,direct torque control(DTC) and direct suspension force control(DSFC) strategy and the digital control system of BPMSM.The main work from this thesis is presented as follows:Firstly,based on the fundamental principle of BPMSM,the mathematic models of BPMSM are given.The shortcomings of traditional suspension force control method are analyzed.Then the DTC and DSFC strategy is used to control BPMSM.Secondly,the theory and method of DTC for traditional permanent magnet synchronous motors are applied to the torque control of a BPMSM in the paper.With the reference of DTC,a double closed-loop control system,in which the inner closed-loop is radial suspension force loop and the outer closed-loop is rotor radial displacement loop,is constructed to control the radial suspension forces directly.The DTC and DSFC algorithm based on space vector pulse width modulation(SVM) strategy is deduced,and the DTC and DSFC system for a BPMSM are designed and simulated by Matlab software.The structure of control system is simple and control system has strong robustness.The simulation results have shown that the rotor can be suspended stability,and torque and radial suspension forces can be controlled independently,and the system has a good static and dynamic performance.Finally,based on the principle of DTC and DSFC strategy,the digital control system is constructed using TMS320LF2407A of TI Corporation,the tiardware and software of digital control system are designed,and the flowcharts of each functional block of software are presented.