Research On Novel Topology And Control Strategy Of Open-winding AC Motor Drive

As the core components of China’s major strategic fields such as computer numerical control machines,robots and rail transit equipment,modern AC motor drive based on power electronic converters have developed rapidly in recent years.To meet the stringent performance requirements in terms of power density,operating range and fault tolerance,the novel drive topologies and control strategies have become a research hotspot in the field of power electronics and electric drives.Among them,the open-winding AC motor drive has received extensive attention from academia and industry in recent years due to its advantages of high DC voltage utilization,fast dynamic response,high control freedom degree,and excellent fault-tolerant capability.However,by reviewing the development history and the state of the art,it is found that due to the requirement of two sets of converters,the defects of cost,efficiency and power density seriously limit the large-scale production and application of the open-winding motor drive.Therefore,this dissertation takes the open-winding AC motor drive system as the research topic,and studies the new topology and control algorithm of the DC-biased open-winding system,the conventional sinusoidal open-winding system and the multi-phase open-winding system in turn.The theoretical basis of the new open-winding motor drive technology represented by series-winding topology is proposed.It realizes the comprehensive optimization of key performances such as system cost,power density,operating efficiency,speed regulation range and fault tolerance.First of all,this dissertation starts with the DC-biased open-winding system.The capacity and number of power devices in the open-winding H-bridge topology is gradually reduced through two optimized paths of current path splitting and leg multiplexing.Based on the analysis,the three-phase series-winding topology,the core structure of this dissertation,is proposed.Compared with the H-bridge topology,the number of power devices are reduced by one-third and the power loss is reduced by more than 20% in series-winding topology,greatly optimizing the system cost,size and efficiency.It has laid the foundation for its large-scale commercial application in the low-cost civilian field.To fully exploit the control performance of the series-winding topology,this dissertation further studies its three-dimensional(3D)voltage modulation strategy.First,a 3D space-vector modulation strategy is proposed.The 3D voltage control capability is realized and the DC voltage utilization reach up to 100%.Then,to simplify the calculation process,a synchronous vector carrier-based modulation strategy is proposed,which can effectively save the computing resources and extends the linear modulation range.On this basis,the series-winding topology with 3D voltage control capability is successfully applied to the conventional sinusoidal open-winding system.The experiments verify that the series-winding topology can effectively extend the speed regulation range,also improve the operating efficiency and torque output capability in the high-speed operating area.Further,to improve the efficiency and torque capability of the series-winding topology below the rated speed,this dissertation proposes the concept of torque/speed mode topology for high and low speed operating conditions,and studies the transient control method of online flexible shifting between various topologies.Through the selection of the mode topology,the design of the shifting circuit and process,the dual-mode series-winding topology shifting structure and the half-bridge/series-winding topology shifting structure are successively proposed.Through in-depth analysis of the control stability mechanism during shifting transients,a step-by-step shifting strategy is proposed to avoid motor runaway.Combined with the zero-axis control capability,a zero-current shifting strategy is proposed,which solves the problem of electromagnetic shock of the shifting switches and the torque fluctuation during the transient.Under various working conditions such as constant speed loading,sudden acceleration/deceleration,and weak magnetic operation,the validity of the topology flexible shifting technology is verified.The experimental results show that the proposed method can realize the flexible switching of online topology in milliseconds without affecting the motor torque and other motion control,thereby extending the operating range and improving the efficiency,which is suitable for new energy vehicles and rail transit applications.Finally,the extended application of the series-winding topology in the multi-phase open-winding AC motor system is realized.Through the detailed analysis of the structure characteristics of the multi-phase series-winding topology,the influence mechanism of the winding arrangement on the key performance is revealed.Thereby,the optimal phase sequence arrangement method is proposed,and the maximum DC voltage utilization can reach 100%,while reducing the number of legs from 2N to N+1 in a N-phase motor(N>3 and N is natural).Further,aiming at the issue of complex control algorithms,a unified carrier-based modulation strategy is developed.It enables the series-winding topology will full freedom degree of voltage control capability for any phase and arbitrary winding arrangement.The proposed method also effectively reduces the demand for computing resources.Finally,while reducing the number of power devices in the multi-phase open-winding topology by nearly 50%,a complete voltage control degree of freedom and100% of DC voltage utilization are achieved.