Design And Research Of Six Phases Fault Tolerant Permanent Magnet Motor And Its Control System

With the development of more electric aircraft and hybrid electric vehicles, the reliability and security of these systems are highly demanded in recent years. Hoping a system can still work reliable when the motor drive system encounter some failures. Therefore, the research of fault tolerant permanent magnet motor and its control system has become the focus research area all over the world. The words fault tolerant in engineering means that the whole system can not only operate stable and reliable under an acceptable performance by isolating the failure components from the system, but also take appropriate measures to maintain the function of its provisions when one or more key components failure. The main purpose of this thesis is to study and design a highly reliable fault-tolerant permanent magnet motor and its control system. The motor can output required power with little speed changes and minimize output torque ripple when one or more phases failures of the motor. Thus, the strong fault-tolerant ability of a motor drive system can be achieved.A detailed analysis of fault-tolerant permanent magnet motor structure and characteristics is established in this thesis. The magnetic isolation, physical isolation and thermal isolation between phases are realized by making each winding wounded around every other tooth of the FTPMM, and every winding is controlled by corresponding H-bridge inverter, which leads to electrical isolation between phases. Design a large harmonic leakage inductance and slot leakage inductance to inhibit the short-circuit current. A 12 slots 10 poles magnet FTPMM structure is identified after studying the winding factor, cogging torque ripple, radial magnetic pull and the selection of power devices effect which produced by the selection of the number of stator slots and rotor poles. In order to achieve a high-performance control of the system, a centrifugal magnetic steel structure is proposed in this thesis to obtain a low sine distortion rate of fundamental back-EMF waveform and reduce the cogging torque ripple value.The main difference between the general permanent magnet brushless motor and the FTPMM is whether it has the ability to inhibit the short-circuit current. Therefore, the analysis of the armature winding inductance and its analytic expression has become one of the major tasks of FTPMM design. By analyzing magnetic line distribution inside the motor, it is found that the winding inductance composed of magnetizing inductance, harmonic leakage inductance and slot leakage inductance. In this thesis, motor reluctance network is established and the relationship between different inductance proportional is obtained, also introduce both slot magnet voltage parameter and the calculated parameter of slot thickness, on the basis of these mentioned above, the precision analytic expression of nonlinear winding inductance and its components is achieved .Using the analytical method to analyze the electromagnetic field of the FTPMM with centrifugal rotor magnet and taking the effect on flux density produce by the slot into consideration to get the analytic expression of the radial flux density and tangential flux density of air gap. The analytic expression of no-load back-EMF and the cogging torque ripple has been derived respectively based on these mentioned above. The analytic expression is obtained to facilitate optimal design of the motor, also has been verified by magnetic field finite element analysis.According to the requirements of the load torque and dynamic response of electric actuator of the aircraft, this thesis not only calculate the effective length of stator's diameter and axial of FTPMM directly, but also derive the electromagnetic design analytic expression of FTPMM. An optimal design-criteria of FTPMM is proposed on the basis of the characteristics of FTPMM to inhibit short-circuit current and get high output performance (low sine no-load back-EMF distortion and the cogging torque ripple) as the optimization objective. A 750W 10 phase 6 poles fault tolerant permanent magnet principle prototype and a 7.5kW engineering prototype motor is built for aviation. The design of the motor is correct and reasonable through the generation test, magnetic isolation test and winding short circuit test respectively.Mathematical model and Matlab/Simulation model of the 10 phase 6 poles FTPMM are proposed in this thesis, also analyze the electromagnetic torque under normal state and fault state of motor drive system. A current direct control strategy is proposed based on the power conservation principle. The strategy is to control each phase winding separately and do not need the hardware identification signals or switching the software algorithm. The FTPMM and its control system achieved strong fault tolerance ability by compensating the average electromagnetic torque of the fault phase. The strong fault tolerance means that when one phase, two phases or three phases of motor or converter failure, the motor system can still output 100%,80% or 60% rated power respectively without speed changes. Multi-phase fault combination test have been taken to verify the fault tolerance ability of FTPMM system based on the current direct control strategy.The fault tolerant system which based on the current direct control strategy has lots of advantages like simple and reliable. But there is periodic pulsation when the system under fault state, as a result, the current direct control strategy can only applied to the situation that torque ripple is not sensitive, especially high speed and large inertia situation. In order to overcome this disadvantage, the torque pulsation of different fault states is analyzed using the vector method, and an optimal current control strategy is proposed to minimize the torque ripple under the fault state by compensating the average electromagnetic torque of fault phase and offsetting the torque ripple of fault state, the proposed strategy could not only achieve with strong fault tolerance but also improve the output performance under the fault state of the system. The simulation based on Matlab and experiments have been taken to verify its correctness.A 7.5kW 10 phase 6 poles fault tolerant permanent magnet prototype motor is built for aviation on a certain plane model to reflect the engineering application value of the motor design and fault tolerant control scheme proposed in the thesis. The design of the motor is correct and reasonable through the generation test, winding short circuit test and single-phase fault state test respectively. These tests show that the prototype and control strategy can achieve desired fault tolerance ability.