| Due to the advantages of high efficiency and power density,rare-earth permanent-magnet synchronous machines(PMSMs)are widely used as driving machines in electric vehicles.However,since the permanent-magnet field is difficult to regulate,the wide-speed-operation capability of the PMSM is limited and highspeed efficiency is lower.To solve the problems above,scholars from home and abroad propose variable-flux machines(VFMs),which can regulate permanentmagnet field by pulse magnetic field through armature winding.The variability of the permanent-magnet field makes the VFM possess excellent speed-expanision capalibity and high efficiency among wide-speed range.The output torque of the traditional series-magnetic-circuit VFM is higher,but the permanent-magnet-field regulation range is limited,which leads to poor wide-speed-operation capability.A reverse-salient series-magnetic-circuit I-Λ-magnetic-pole variable-flux machine(RSSⅠΛ-VFM)is proposed in this thesis.The I-Λ-magnetic-pole structure can broaden permanent-magnet-field regulation range while ensuring output torque of the machine,thereby improving the wide-speed-operation capability of the machine.The main research works of this thesis are as follow:Firstly,the topology of RSSⅠΛ-VFM is proposed,and the working principle of the machine is illustrated.The RSSⅠΛ-VFM is compared with a typical seriesmagnetic-circuit variable-flux machine.Based on the equivalent magnetic-circuit model,the permanent-magnet matching law of the machine is researched.The influence of magnet dimensions on critical remanent ratio of the low-coercive-force magnet is analyzed.Based on the analytical method,the magnet selection principle for improving permanent-magnet flux linkage of the machine is given.In terms of torque-output capability,magnetic stability under load condition and permanentmagnet-field regulation range,the proposed topology is compared with a typical series-magnetic-circuit variable-flux machine.The research results show that the proposed topology possesses better speed-expansion capability and overload capability.Secondly,the wide-speed design method of RSSⅠΛ-VFM is researched.Aiming at the problem that the wide-speed-operation capability of RSSⅠΛ-VFM is reduced because of unsuitable matching of machine parameters,expressions of torque and speed of the machine with different current-control strategies are derived by analytical method.The influences of magnetization states,machine parameters,controller capacity,etc.on torque-speed characteristics are analyzed.Based on analytical and graphical methods,the design method for RSSⅠΛ-VFM with widespeed-operation range is given,which is verified by finite element method.Aiming at the problem that the machine is demagnetized due to large d-axis current during speed expansion,the influence of d-axis current limit on the wide-speed-operation capability of the machine is analyzed.Based on the subdivision of magnetization state,a compensation method to reduce torque and speed loss is proposed.Thirdly,the electromagnetic characteristics of RSSⅠΛ-VFM under different winding arrangements and magnetization states are studied.The expressions of stator magnetomotive force(MMF)with time and space are derived for RSSⅠΛ-VFM.The influence of winding arrangement on the re-magnetization characteristics and electromagnetic torque of the machine is analyzed.The principle of the machine winding layout is obtained.The inductance characteristics and electromagnetic torque of the machine under different magnetization states and load currents are researched.A salient ratio adjustment method is proposed to improve the magnetic stability of low-coercive-force magnet under load condition and the torque-output capability at high-speed range.The constant-power characteristics and efficiency characteristics of the machine under different magnetization states are researched,and the magnetization state distribution diagram of the machine at full-speed range with high efficiency is given.Then,the electromagnetic vibration characteristics of RSSⅠΛ-VFM is researched.Based on the complex relative-permeance method,the distribution function of electromagnetic force wave considering the stator and rotor slotting effect is derived.The distribution laws of radial and tangential electromagnetic force waves under different magnetization states and re/demagnetization conditions are analyzed.The modal frequencies of the stator assembly of RSSⅠΛ-VFM are analyzed.The influence of static and dynamic magnetizations on machine magnetization vibration is analyzed.The spectrum characteristics of triangular,trapezoidal,square and sinusoidal wave pulse currents are analyzed by analytical method.The duration time calculation method of pulse current to reduce magnetization vibration is proposed,which is verified by finite element method.The influence of the magnetization state on the electromagnetic vibration of the machine under the same torque-speed condition is analyzed,and the magnetization-state selection method to reduce machine vibration is given.Finally,a protype of RSSⅠΛ-VFM is manufactured.The experimental platform is built,and relevant experimental is carried out.The re/demagnetization characteristics,no-load back electromotive force(EMFs),electrical parameters,torque characteristics,wide-speed-operation characteristics and vibration characteristics of the machine are tested.The test results of prototype are basically consistent with simulation results.The proposed machine possesses wide permanentmagnet-field regulation range while ensuring the machine output torque and overload capability. |
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