| The PWM of ac speed regulating is researched in this paper. The method of Hybrid SVPWM- the way of improving the two-level SVPWM is used, through comparing with the normal SVPWM in order to show its advantages. The structure , principle and SVPWM of three-level inverter is discussed in detailed, and the implementation method of combining it with the DTC control of PMSM is analyzed. A simulation model of control system is given based on Matlab/Simulink, whose simulation result is consistent with the analysis of theory. At last the method of backstepping is used in the position control of PMSM, whose result is satisfied.Firstly, the structure and the mathematics models of PMSM are analyzed in the paper, and the motor model is simplified through introducing the various coordinate, and then the voltage, flux and torque equations of the motor are got. The principle of PWM and SVPWM is analyzed, on the basis of which the RMS method analysis of flux linkage is introduced, and the paper find a better way to subdivide the sector through the change of the sequences of vectors, which is method Hybrid SVPWM. We can find that this method reduces the harmonic component of current by analyzing the result of simulation and FFT.Secondly, the topology and operation principle of three-level inverter is researched on the basis of two-level inverter, and the method to achieve its SVPWM is carried out. Then analyze the principle of the DTC of PMSM, and further find a way to combine the SVPWM of three-level with DTC, and set up the sub-modules of PMSM DTC system by Matlab/Simulink. And the simulation results show the method is successful, proving the better control effect of three-level inverter than the two-level.Thirdly, Backstepping-a motor nonlinear control method is analyzed, and the control method of backstepping is realized by combination with the mathematics model of PMSM. At last verify the feasibility of this method through the simulation.
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