Design Of Zero Sequence Current Control Strategy For Open-Winding Permanent Magnet Synchronous Machines

Compared with the permanent magnet motor of conventional form,Open winding structure that opens the neutral point of the motor winding has been widely concerned and studied by scholars at home and abroad due to its advantages over multilevel operation and fault-tolerant control.Open winding permanent magnet motor can be divided into two different structures: isolated structure with dual power supply and common DC bus structure with single power supply.Common DC bus structure is wildly used because of the small volume and low cost.However,zero sequence loop exists in this structure,so how to effectively suppress the zero-sequence current has become an important research topic.The aim of this paper is to suppress the zero-sequence current in open winding permanent magnet motor with common DC bus structure,and the main contributions are as follow:(1)The mathematical model of the open winding permanent magnet motor in the three-phase stationary coordinate system and the two-phase rotating coordinate system is established.The spatial distribution and characteristics of voltage vector converter are analyzed when isolated structure with dual power supply is adopted.Optimize the dual converter space vector modulation strategy considering the output of common mode voltage.(2)A closed loop control strategy for the suppression of zero-sequence current is proposed.The suppression of zero-sequence current is achieved by controlling the output voltage of the converter to compensate the three times harmonics of the motor stator back EMF.The virtual three phase current is constructed and converter the zero-sequence current to dc component through coordinate transformation,then a two degree of freedom linear controller is designed to effectively suppress the zero-sequence current.In addition,the characteristics of the two degree of freedom linear controller and the method of parameter tuning are discussed and the stability of the controller is analyzed.Finally,a closed loop control simulation model is established to verify and analyze the performance of the control strategy on zero-sequence current suppression.(3)Finite state model predictive control is presented in this paper,suppression of zero sequence current by inhibiting the converter output common-mode voltage.The tem of the Common-mode voltage suppression is added in the system evaluation function,the common mode voltage suppression weighting factor and switch combination selection method on its control effect is analyzed.In order to suppress the zero sequence current reduce the motor torque fluctuation at the same time,virtual vector synthesis principle is analyzed and the model predictive control method based on virtual vector is put forward.On this basis,the simulation model is established,the control effect of the two kinds of control strategy is verified and analyzed.(4)The open-winding permanent magnet motor experimental platform is built,laying the foundation for the experiments of the zero sequence current suppression and other control experiments of open-winding permanent magnet motor.Finally,open-winding permanent magnet motor load on the platform,the dq axis current response characteristics were analyzed in the different controller bandwidth and different sampling period.