| With the development of power electronics and micro-electronics,phase number is not a restriction in the system design,and the multiphase motor drive system has also received more and more attention from scholars.Compared with conventional three-phase motor,multiphase motor has the advantages of large power output with low voltage,good fault tolerant ability.It is suited for some application areas,such as electric ship propulsion,electric vehicles and aircrafts.High performance multiphase motor drive system has higher requirements for bus voltage utilization.Overmodulation technique can make the multiphase inverter work in the nonlinear modulation region,improving the bus voltage utilization rate and expanding the motor speed range.Dual three-phase permanent magnet synchronous motor(Permanent-magnet Synchronous Motor,PMSM)which has two sets of three-phase windings phase shifted by 30 electrical degrees is chosen as research object.Its overmodulation technique are deeply studied in this dissertation.The main contents are as follows:Firstly,according to the corresponding coordinate transformation matrix,the models of dual three-phase PMSM are set up in the traditional reference frame,double d-q reference frame and vector space decomposition(Vector Space Decomposition,VSD)reference frame.And three vector control strategies related to the three models are compared and analyzed.Based on the theory of multi-dimensional space decoupling,this paper describes the basic principle of dual three-phase space vector pulse width modulation(Space Vector Pulse Width Modulation,SVPWM)technique in detail,and analyzes several common dual three-phase SVPWM algorithms.Secondly,Two-vector method and virtual vector method have the disadvantage of insufficient degrees of freedom.Based on the nearest four-vector SVPWM algorithm,this paper proposes a dual three-phase four degrees of freedom SVPWM overmodulation algorithm based on virtual vector.The fifth harmonic content which needs to be optimal controlled is deduced in detail in the overmodulation region according to the modulation ratio.The fundamental wave and the harmonic subplaces are controlled at the same time without reducing control degrees of freedom,effectively reducing the low harmonic content of output voltage.Through simulation,effectiveness and correctness of the overmodulation strategy proposed in this paper is verified.In order to verify the proposed modulation strategies,a dual three-phase inverter experiment platform has been built and corresponding hardware circuit and software module have been designed.Based on the experimental platform,a series of comparative experiments have been carried out,verifying the correctness and feasibility of the proposed new modulation strategies. |
