Research On Torque Ripple Reduction Strategy For Open-Winding Permanent Magnet Synchronous Machine

Open-winding permanent magnet synchronous machines(OW-PMSMs)gain increasing research focus in recent years due to its advantages including high power density,flexible control capability,and enhanced fault-tolerant capability.However,a low impedance zero-sequence electrical path exists in the OW-PMSM with a common DC bus.Significant uncontrolled zero-sequence current will consequently result in undesired high-frequency torque ripples.Besides,under non-zero power factor angle(PFA)condition,the current clamping problem exists in the semicontrolled open-winding permanent magnet synchronous generator(OW-PMSG)system,which also results in torque ripples.Therefore,this paper investigates the torque ripple reduction strategies for the OW-PMSM.In this paper,the virtual three-phases expansion method is firstly designed based on the zero-sequence equivalent circuit.Particularly,this method can transform the zero-sequence current to the current vector in the synchronous rotating coordinates.The zero-order-hold discretization OW-PMSM model with control delay is then established.On this basis,the state-space method is introduced into the controller design process.The dq-axis current controller and zero-sequence current controller are directly designed in the discrete-time domain.Meanwhile,the parameter tuning method is accordingly proposed.Theoretical analysis and experimental results show that the proposed torque ripple rejection strategy can achieve the excellent control performances in both high and low switching frequency conditions.At the same time,in order to improve the torque control performances of semicontrolled OW-PMSG under different PFA conditions,this paper proposes a torque ripple rejection strategy based on the virtual zero-crossing detection method and zero-sequence current segment injection method.First,the current zero-crossing phenomenon under different PFA conditions is analyzed.Based on the analyses above,a virtual zero-crossing detection method is proposed to reduce the impacts resulting from the non-ideal factors(e.g.sampling noises)existing in the OW-PMSG system.And a zero-sequence segment injection method is proposed to solve the current clamping problem existing in the none-zero PFA situation.Theoretical analysis and experimental results show that the proposed control strategy can not only solve the current clamping problem,but also effectively reduce the torque ripples.In addition,different from the above control strategies in which the linear controllers are adopted,the variable-action-period-based predictive control strategy is proposed in this paper.In the proposed strategy,the cost function that only contains the flux error is constructed.The optimal voltage vector and its optimal action period are both obtained by means of the two-step cost function minimization method.Moreover,the corresponding digital implementation method for the proposed strategy is investigated.The comparison experiment results show that the proposed control strategy can not only reduce the harmonic components of three-phase currents,but also achieve the better torque control performances.