Research On Current Harmonic Suppression Strategy Of Slotless Motor Based On Three Level Converter

The traditional strucutre of the permanent magnet synchronized motor(PMSM),due to the existence of slot,will cause a series of electromagnetic problems.The subject controlled in this paper which adopt a two phase slotless structure was designed to used in the special field.The motor has the advantages of low cogging torque,but its inductance is smaller than that of the conventional structure motor.Thus,it is difficult to control the current effectively by using the conventional voltage sourse inverter which will cause the problem of high current harmonics.In this paper,the SVPWM control strategy based on the two phase three-level inverter is introduced,which effectively suppressed the current harmonics of the slotless motor.Firstly,based on the analysis of the principle of two-phase motor,the simulation model of two-phase motor is constructed according to the parameters and characteristics of the controled subject.By comparing differernt current harmonic suppression methods,the flying capacitor three-level full-bridge topology is used as the main circuit structure of the control system.The simulation model of the control system is built in Matlab/Simulink to complete the PS-SPWM control strategy simulation verification.The current harmonic suppression effects of both the three-level drive system and traditional drive system is then compared.Secondly,the classical three-level SVPWM control strategy is designed for the three-level full-bridge topology chosen in this paper,and the implementation method of the control strategy is introduced in detail.The voltage output of the classical three-level SVPWM control strategy is ladder wave which helps to suppress the current harmonic.In order to improve the current change frequency and further suppress the current harmonics of small inductance slotless motor,an improved three-level SVPWM control strategy is designed.The current change frequency is twice as high as that of classical control strategy.Thus,the new control method is more suitable for the current harmonic suppression.Thirdly,in order to simplify the implementation of the improved three-level SVPWM control strategy,this paper designs an equivalent control algorithm.Based on the three-level PS-SPWM modulation strategy,two output voltage frequency doubling methods,namely,modulation wave decomposition method and carrier amplification method,are given to derive the equations of modulation wave and carrier wave,so that the equivalent control strategy could generated the same effect as the improved SVPWM control strategy,while simplifying the implementation process at the same time.Finally,the voltage harmonics of the improved three-level SVPWM control strategy are analyzed theoretically,and the relationship between the high frequency harmonic component and the switching frequency is given.The current harmonic suppression effect of adjusting the voltage output of the inverter and shortening the current change time is deduced.It is proved that the improved three-level SVPWM control strategy can effectively suppress the current harmonics of the slotless motor.