Research On Fault Tolerant Permanent Magnet Motor And Its Control System In Electromechanical Actuator

As the major actuating mechanism of an aircraft, electromechanical actuators havehigh requirements for reliability and fault tolerant. In this dissertation, a fault tolerantpermanent magnet motor is proposed to minimize the size and to improve the faulttolerant and reliability of the electromechanical actuators. A sensorless rotor positionestimation method for the fault tolerant permanent magnet motor is presented, and avector control system for the fault tolerant permanent magnet motor based on matrixconverter is studied. The main contents and contributions are as follows.1. According to the requirements of the reliability, fault tolerant and size of theelectromechanical actuator on an aircraft, the direct drive electromechanical actuator isproposed, and the structure and size of the fault tolerant motor are investigated. On thisbasis, the internal diameter of the stator is optimized to minimize copper loss. Ananalytic expression of the tooth tip leakage inductance is derived using the flux tubeapproach, and some slot and tooth parameters which have remarkable influences on thetooth tip leakage inductance are found, and they are optimized by the finite elementmethod. The fault tolerance of the motor is simulated using the finite element method,and the results show that the motor has a perfect property in the magnetic isolation andfault tolerant, and it meets the fault tolerant requirements on the direct driveelectromechanical actuator.2. For the complex slot configuration of the fault tolerant permanent magnet motor,the air gap magnetic field distribution is divided into two parts: the magnetic fielddistribution produced by the current through the armature windings, and the magneticfields produced by the permanent magnets of the motor. The slotted structure of thefault tolerant permanent magnet motor is transformed to a simpler geometrical domainutilizing the Schwarz-Christoffel transform, and the magnetic field distributiongenerated by the current through the armature windings is then analyzed. The magneticfields of the permanent magnets are represented by the magnetic fields generated by anumber of line currents, and the magnetic field distribution produced by the permanentmagnet is analyzed. The accuracy of the results is validated by the finite elementmethod. Summing up the two parts of the magnetic fields, the cogging torque andelectromagnetic torque are calculated as well.3. The magnetic saturation saliency effect is analyzed, and the total flux linkage ofa winding is separated into the flux linkages produced by the stator current and by therotor permanent magnet. The nonlinear mathematical model of the fault tolerantpermanent magnet motor is established. An estimation method for the rotor position ofthe fault tolerant permanent magnet motor, which is based on the high frequencyvoltage signal injection method, is presented. The simulation results show that the high frequency voltage signals have little effect on normal operation of the motor, and themethod can accurately estimate the position the rotor. The initial rotor position of thefault tolerant permanent magnet motor is estimated by injecting a voltage pulse vector.The simulation results indicate that the proposed approach is able to detect the initialposition of the rotor.4. By introducing the principle of the matrix converter, the matrix converter isequivalent to the combination of a virtual rectification and a virtual converter, and thecontrol strategy of the matrix converter based on voltage compensation is proposed.Based on the analysis of the advantages and disadvantages of the PI current loop and thetime-optimal current loop, a control system for the matrix converter based on asub-optimal current loop is designed. The vector control system for the fault tolerantpermanent magnet motor based on the matrix converter is studied, and the simulationresults show that the system holds good dynamic response performance and adaptationcapability.5. Based on the matrix converter, a sensorless vector controller for the faulttolerant permanent magnet motor is designed, and the dynamic performance of thecontrolled system is simulated for the cases when the motor is on the normal state andthe fault state. The results show that the controlled system can accurately track theinputs when the motor is normal, and the system can still work when short circuit oropen circuit faults occurs in the motor, and the designed system well meets the faulttolerant requirements for the direct drive electromechanical actuator.