Research On Drive And Fault-tolerantcontrol Technologies Of Dual Three-phase Permanent Magnet Synchronous Motor

With the rapid development of power electronics, the motor drive systems have got rid of the phase number constraint form traditional three-phase power supply network. Multiphase motors enjoy the advantages of low-voltage highpower, low-torque pulsation, and good fault tolerant ability. They are suited for application fields such as electric vehicles, wind power generation, and aerospace applications. With the dual three-phase permanent magnet synchronous motor(PMSM) as the research object, the mathematical modeling, harmonics suppression, overmodulation, and fault tolerant control strategies are deeply studied in this dissertation.Firstly, the magnetic motive force(MMF) harmonics of multiphase motor windings are analyzed, and it reveals the theoretical foundation of the low-torque pulsation characteristic for dual three-phase PMSM. The model of dual three-phase PMSM is built up according to the vector space decomposition(VSD) theory. The advantages and disadvantages between the two-dimensional current vector control and the four-dimensional current vector control are compared. The significance of harmonic subplane variables in VSD model is analyzed. The effect of six-phase voltage source inverter(VSI) dead-time and asymmetric parameters for two sets of three-phase windings can be compensated by the control of harmonic subplane currents. There are large 6k±1(k=1,3,5,…) harmonic currents in the z1-z2 subplane when the basic voltage vectors are adopted in switching-table-based direct torque control(DTC) for dual-three phase PMSM drives. By introducing the principle of pulse width modulation, the voltage vector is modified; both simulation and experimental results demonstrate that the harmonic currents in the z1-z2 subplane can be suppressed significantly when the modified intermediate vectors are adopted for DTC.Secondly, the pulse width modulation(PWM) strategies for the six-phase VSI are studied. The PWM waveform was asymmetrical and the switching loss was large when the four-vector space vector pulse width modulation(SVPWM) was adopted for six-phase VSI. So the double zero-sequence injection PWM strategy based on carrier-based pulse width modulation(CBPWM) was more appropriate for four-dimensional current vector control. The inner relationship between the double zero-sequence injection PWM strategy and the four-vector SVPWM is analyzed. A dual zero sequence injection PWM strategy based on CBPWM for a five-leg inverter supplying dual three-phase PMSM system is proposed, including mean continuous PWM and three kinds of discontinuous PWM modes, and the bus voltage utilization ratio is analyzed. This strategy can achieve the maximum bus voltage utilization, and is easy to implement. It is a possible solution for fault-tolerant in the case of an fault in one leg of the six-leg inverter.Thirdly, the overmodulation strategy for dual three-phase PMSM is studied. Four-vector SVPWM renders mathematic foundations. By introducing the concept of the intermediate vector and analyzing the required harmonic voltage injection, two overmodulation algorithms were proposed. The second algorithm achieves the minimum harmonic injection and is able to decrease the harmonic currents in the overmodulation region most greatly. The modulation algorithms in both linear and overmodulation regions have been unified and implemented with the double zero-sequence injection PWM strategy. This strategy is able to overcome the inherent shortcomings of the four-vector SVPWM, and it achieves smooth transitions from linear to overmodulation region. The minimum-magnitude-error overmodulation strategy is adopted for the full utilization of the six-phase inverter. Simulation analysis and experimental results demonstrate the effectiveness and feasibility of the proposed strategy.Lastly, the control strategy for dual three-phase PMSM due to open phases is studied. The common fault-tolerant control strategy for multiphase machines need set up the reduced order system model. There are two different neutral connections for dual three-phase PMSM under open phase conditions and each case corresponds to a different decoupled transformation matrix, so they need to be modeled, respectively. When an open-phase fault occurs for dual three-phase machine, the voltage, flux, and torque equations are unaffected by the fault. The fault-tolerant control strategy based on normal decoupling transformation is constructed in this paper. This control strategy is suitable for the two different neutral connections, and only modifications of current references in the harmonic subplane are needed. The influence of three harmonic magnetic potential on the electromagnetic torque is analyzed. Theoretical analysis and experimental verification were done for one open phase and two orthogonal open phases. The experimental results demonstrate the effectiveness and feasibility of the proposed strategy.