Research On Driving System Of T-Type Three-Level Inverter Fed Open-End Winding Motor

In recent years,the open-end winding topology has gradually emerged and is widely used in transportation,ship propulsion,and industrial production.There are many choices of inverters on both sides of the open winding topology.In this paper,T-type three-level inverters are selected as power conversion modules,which can output five levels,with high output power,high output voltage level,flexible and diverse modulation methods and strong fault tolerance performance and so on.The T-type three-level inverter fed open-end winding topology is researched in this paper.A dual-threshold current hysteresis control strategy is proposed for permanent magnet motors whose back-EMF waveforms are not sine waves,such as the Doublysalient Permanent Magnet(DSPM)motors.Corresponding space vector pulse width modulation(SVM)strategies have been proposed for permanent magnet motors such as traditional three-phase motors and dual three-phase motors.The proposed control strategies are verified by both experiments and simulations.The thesis firstly mathematically modeled the three-phase Doubly-salient Permanent Magnet(DSPM)motor with non-sinusoidal back EMF waveform,the three-phase permanent magnet synchronous motor with sinusoidal back EMF waveform and the two-phase permanent magnet synchronous motor.The working principle is introduced.Aiming at the Doubly-salient Permanent Magnet(DSPM)motors whose back-EMF waveform is not sine wave,in order to make full use of the characteristics of the T-type threelevel inverter open winding topology able to output five levels,a double-threshold hysteresis control strategy is proposed in this paper.According to the three working states of the T-type three-level inverter and the circuit structure of the open-winding topology,the output five different levels of different switching state groups of the inverters on both sides of the phase winding are analyzed,and the output voltage level is selected according to the current error.The calculation method of the reference currents of the Doubly-salient Permanent Magnet motors under the double-shot control is introduced.At the same time,an appropriate midpoint potential balancing strategy is proposed.In addition,the advantage of directly suppressing zerosequence current under the control of current hysteresis is also obtained.For the permanent magnet three-phase motor whose back-EMF waveform is a sine wave,a 120°vector decoupling-based dual SVM control strategy is proposed in this paper.The space voltage vector diagram of the open winding three-phase topology of the T-type three-level inverter is the same as the space voltage vector diagram of the five-level inverter.The number of voltage vectors is large,and it is difficult to design the control strategy.The proposed control strategy re-decouples the five-level inverter space vector into the space vectors of two T-type three-level inverters,and turns the control of the five-level inverter into the control of the two three-level inverters.Independent control reduces the difficulty of control,and can completely eliminate the zero-sequence voltage in the open winding of the common bus structure.An SVM control of an independent T-type three-level inverter is proposed,which uses three nearest voltage vector vectors of the reference voltage vector to perform voltage synthesis,and can simply and effectively maintain the midpoint potential balance.Aiming at the fact that there is still a small zero-sequence current in the actual experiment,an additional zero-sequence current suppression strategy is proposed.In this paper,a four-SVM control strategy is proposed for a permanent magnet dual threephase motor whose back-EMF waveform is a sine wave.The parameters of the reference voltage vectors Uα,Uβ,Ux,and Uy calculated by the PI controller after vector decoupling and transformation are re-inversely decoupled and transformed back to the six-phase stationary coordinate system to obtain the six-phase winding reference voltage vector.Re-establish two three-phase stationary coordinate systems for independent control.This can suppress the harmonic components of the x-y sub-plane.In the end,the system becomes SVM control of four independent T-type three-level inverters,which reduces the control voltage level and reduces the control difficulty.And an additional zero-sequence current suppression strategy is proposedFinally,the paper builds a hardware experiment platform,and the experiments verify the dual-threshold hysteresis control strategy based on the T-type three-level inverter fed openwinding doubly salient permanent magnet motor,and the 120° vector decoupling double SVM control strategy based on the T-type three-level inverter fed open-winding three phases PMSM and the four SVM control strategy based on the T-type three-level inverter fed open-winding dual-three phases PMSM.