Research On Control Strategies For Dual-inverter Fed Open Winding Permanent Magnet Synchronous Motor System With Common DC Bus

Permanent magnet synchronous motor(PMSM)is widely used in industrial,aerospace and military fields due to its advantages of simple structure,high power density and good control performance.In order to further satisfy the requirement of high-voltage and high-power system,a novel open winding(OW)PMSM is proposed which is configured by opening the neutral point of the motor stator winding so that it can be fed by two inverters.Due to the dual-inverter structure,OW-PMSM system has multi-level output characteristics and high fault tolerance.The power supply modes of OW-PMSM system mainly include isolated power supply mode,hybrid power power supply mode and common DC bus power supply mode.Among them,the common DC bus power supply mode has attracted wide attention because of its low cost and small volume.Therefore,this paper takes the dual-inverter fed OW-PMSM system with common DC bus as the research object and especially focus on the control strategies for this system.Since the conventional direct torque control(DTC)strategy doesn’t suppress the zerosequence current(ZSC),this paper proposes a DTC strategy based on an integrated voltage vector(VV)look-up table.Firstly,a novel look-up table is established and two VVs are determined based on the torque,flux linkage and the ZSC control signal.One VV produces a null zero-sequence voltage(ZSV),which is employed to control the torque and flux linkage,and the other VV is employed to produce a ZSV to eliminate the effect of the rotor harmonic flux on the zero-sequence loop and achieves ZSC suppression.This strategy achieves effective ZSC suppression while retaining the simple control structure of the conventional DTC strategy.It also has a lower switching frequency and wider modulation range than the zero VVs based DTC strategy.The experimental results verify that the proposed strategy has good control performance.Considering that the model predictive current control(MPCC)strategy has better steady-state performance than the DTC strategy,this paper proposes a fast optimal VV selection based MPCC strategy in a 3-D space.Firstly,a cost function related to the stator voltage is established and weighting factors are calculated,then a corresponding 3-D space is established and the position distribution of all candidate VVs in the 3-D space is analyzed.Finally,a fast optimal VV selection principle is determined based on the space geometric theory,and only 4 calculations are required to obtain the optimal VV,which greatly reduces the system calculation time.Due to the fast optimal VV selection based MPCC strategy employes one VV in each control period,which results in the dual-inverter being unable to accurately produce the reference VV,so this paper further proposes a VV tracking MPCC in a 3-D space.Firstly,three basic VVs are determined for producing the reference VVsynthesis.Then the duration time of each basic voltage vector is determined based on the volt-second balance principle.And finally,determine the conduction time of each switching phase is determined.This strategy makes the dual-inverters produce reference VVs accurately,and effectively improves the system steady-state performance.The effectiveness of the proposed strategy is verified by comparative experiments.