Research On Series-Parallel-Permanent-Magnet V-U-Magnetic-Pole Variable-Flux Machine System

Vigorous development of electric vehicles(EVs)is an important measure to achieve the strategic goal of “double carbon”,and it is very helpful to ensure energy security and improve environmental quality.Permanent-magnet synchronous machines(PMSMs),which have the characteristic of high efficiency and high power density,are widely used in EVs.However,due to the use of high-coerciveforce Nd Fe B magnets,PMSMs have some problems,such as the difficulty in adjusting permanent-magnet magnetic field,the limited speed range and the low operating efficiency in high-speed region.To solve these problems,the german scholar has proposed the concept of variable-flux machine(VFM).By adjusting the magnetization state(MS)of low-coercive-force permanent magnets(PMs)and then adjusting the field excitation of machine,the speed range of VFM is widen and the operating efficiency in high-speed region is improved.For the current mainstream series-magnetic-circuit VFMs and parallel-magnetic-circuit VFMs,it is difficult to give consideration to the torque ability and MS regulation ability.A series-parallelpermanent-magnet V-U-magnetic-pole variable-flux machine(SPPM-VUVFM)is proposed in this paper.Through the design of series-parallel variable magnetic circuit,SPPM-VUVFM combines the advantages of high torque ability in seriesmagnetic-circuit VFMs and wide MS regulation range in parallel-magnetic-circuit VFMs.It is expected to promote the development of EV driving machine technology.The main research work of this paper includes following parts:Firstly,the topology and mathematical model of SPPM-VUVFM are analyzed.The topology of SPPM-VUVFM is proposed.The special series-parallel magnetic circuit relationship in the machine is analyzed.The MS regulation principle and variable magnetic circuit characteristic of SPPM-VUVFM are expounded.It is proved that the SPPM-VUVFM combines the advantages of high torque ability in series-magnetic-circuit VFMs and wide MS regulation range in parallel-magneticcircuit VFMs.A neural-network-based high-precision hysteresis model is proposed.The single valued processing of the hysteresis loops and the optimization of the neural network structure are carried out.The research shows that the proposed hysteresis model has the advantage of fast prediction speed and high accuracy.The equivalent magnetic circuit model of SPPM-VUVFM is established.The influence of MS regulation on the air-gap flux is analyzed.The research shows that the calculation accuracy of the established magnetic circuit model is relatively high.Secondly,the effect of the ratio between PMs,the structural parameters and the MS of SPPM-VUVFM on the performance is analyzed.The effect of the ratio between high-coercive-force and low-coercive-force PMs in V-type and U-type magnetic poles,the size and relative position of V-type and U-type magnetic poles,and the width of magnetic bridges on the MS regulation range,the torque ability and the load stability of magnets of SPPM-VUVFM is investigated.The effect of the MS of SPPM-VUVFM on the no-load back EMF,torque,speed range and efficiency is investigated.The optimal MS selection method for SPPM-VUVFM during the wide-speed-range and high-efficiency operation is proposed,which can realize the extension of speed range and the expansion of high-efficiency operating area.Thirdly,the effect of different magnetizing/demagnetizing current trajectories on the characteristic of voltage,torque and energy consumption during the online magnetization/demagnetization process is analyzed,and the optimal current trajectories during the online magnetization/demagnetization process are obtained.The online magnetizing/demagnetizing current trajectories with different waveforms,amplitudes and time durations are compared and analyzed.The effects of machine speed,current waveform,amplitude and time duration on the maximum voltage,torque ripple and energy consumption of SPPM-VUVFM during the online magnetization/demagnetization process are investigated respectively.Considering the influence of magnetizing/demagnetizing current trajectories on the characteristic of voltage,torque and energy consumption during the online magnetization/demagnetization process,the optimal magnetizing/demagnetizing current trajectories of SPPM-VUVFM during the wide-speed-range and high-efficiency operation are determined.Fourthly,the full-speed-range current trajectory planning strategy based on the current minimizing principle is investigated for SPPM-VUVFM.A nonlinear flux linkage model is established to accurately calculate the d-and q-axis stator flux linkage at different MSs.Considering the influence of variable magnetic flux characteristic and parameter nonlinearity,a full-speed-range current trajectory search method based on the current minimizing principle is proposed.The iterative search method based on the double golden selection method is established,which can realize the precise calculation of current-minimizing-control current trajectories at every MS.A full-speed-range online current control method based on the current minimizing principle is proposed.The full-speed-range online current control neural-network model is established.The online calculation of d-and q-axis current command under the current minimizing control at different MSs,load conditions,voltage limit and current limit is realized,and the full-speed-range currentminimizing online current control for SPPM-VUVFM is realized.Finally,a SPPM-VUVFM prototype is developed.The experimental test platform which can complete the characteristic test of both the online magnetization/demagnetization process and the steady-state operation is built,and the performance of the prototype is tested.The experimental test and analysis are carried out on the magnetizing/demagnetizing characteristic,the characteristic of voltage,torque and energy consumption during the magnetization/demagnetization process,the waveform of no-load back EMF,the torque-speed characteristic,and the efficiency characteristic of the prototype,which verifies the accuracy of the theoretical research and simulation analysis in this paper.The experimental results show that the no-load back EMF of machine can be adjusted in a large range.The load stability of SPPM-VUVFM is strong.By adjusting the MS,the operation range of the machine can be widened and the high-efficiency operation area can be expanded.