变磁通记忆电机非线性模型与调磁电流脉冲轨迹优化研究

Research on Nonlinear Mathematical Model and Improvement of Re-/De-Magnetization Current Pulse Trajectories for Variable Flux Memory Machine

变磁通记忆电机(VFMM)克服了传统永磁同步电机(PMSM)气隙磁场不可调节、调速范围受限等缺点,可根据运行工况需求实时地在线调节气隙磁场,具有全域高效运行的优势。该文针对一台混联磁路型VFMM(HMC-VFMM)磁路复杂及非线性强等问题,研究非线性模型的建立及调磁电流脉冲轨迹的优化。首先,测试磁化曲线、电枢磁链特性与电感特性,建立VFMM的非线性模型,以实现电机特性的精确描述;其次,分析正弦型电流脉冲轨迹与所需电压变化特性,并基于此提出一种非对称电流脉冲轨迹与优化方案,在实现充去磁的同时,降低调磁过程产生的损耗;再次,为实现调磁电流的精确控制,基于上述非线性模型,提出一种基于实测参数的前馈电流控制器;最后,通过实验验证所提电流控制器的有效性以及理论分析的正确性。

The development of variable flux memory machine(VFMM)is to tackle the issues of unchangeable air-gap flux and hence limited speed range,which are the main drawbacks of the traditional permanent magnet synchronous machine(PMSM).According to the operating condition,the air-gap flux of VFMM can be adjusted online by injecting a pulse-shaped d-axis current,so that the efficiency under different working points can be enhanced.The existing works in relation to the VFMM drives are rare.Most of them focus on improving the dynamic response of current controller and suppressing the torque fluctuation due to the injection of d-axis current pulse.No scholars have studied the relationship between the re-/de-magnetization current pulse trajectories and the resulted losses.To fulfill the gap,this paper gives a research on the key technical issue.This work is based on a hybrid magnetic circuit VFMM(HMC-VFMM).Firstly,in order for an accurate description on the HMC-VFMM with complex electromagnetic properties,the magnetizing curve,the armature flux characteristic and the inductance characteristic are tested,on which basis,the nonlinear mathematical model is established.Secondly,the sine-shaped current pulse trajectories and the required voltages are analyzed.Then,an asymmetrical current pulse trajectory and its improved method are proposed in order to realize re-/de-magnetization and reduce the associated losses simultaneously.The corresponding voltage curves are analyzed in terms of the maximum amplitude.Thirdly,based on the established nonlinear mathematical model,a feedforward current controller considering the measured parameters is proposed.The proposed current controller is integrated into the mature flux-oriented control.Finally,an experimental test rig based on the prototype of HMC-VFMM is constructed to verify the effectiveness of the foregoing theoretical analyses.The proposed feedforward current controller is tested at first.The control methods with and without the proposed feedforward current controller are compared.The results show that the dq-axis currents regulated by the method with the proposed controller perform better in terms of tracking errors.With the high-performed controller,the control performances of d-axis current with different trajectories and the corresponding voltage values are compared.For re-and de-magnetization operations,the magnitudes of the d-axis current pulse trajectories are set to+30 A and-25 A,respectively.Four trajectories including a sine-shaped current pulse trajectory and three asymmetrical current pulse trajectories with different durations are tested.The results show that the tested three asymmetrical current pulse trajectories can shorten the total time of magnetization processes and don’t enhance the voltage requirement.Then,the losses resulted from the magnetization operations with the four trajectories are measured and compared.The obtained data indicates that using the sine-shaped current pulse trajectory,the losses during re-and de-magnetization processes are 33.58 J and 27.88 J,respectively,and the copper losses account for 82.13%and 70.16%,respectively.With the three asymmetrical current pulse trajectories,the losses can be reduced by 22.57%,11.97%and 1.46%for the re-magnetization operation and are 27.69%,18.62%and 9.43%for the de-magnetization operation.The following conclusions can be drawn according to the experimental results.(1)The proposed feedforward current controller considering measured parameters can improve the current control accuracy.(2)For the conventional sine-shaped current pulse trajectories,the peak value of voltage required for re-or de-magnetization operation appears at the rising stage and decreases gradually with the increase of the designed offset angle.(3)For the proposed asymmetric current pulse trajectories,by improving the duration of the recovery stage,the loss generated in the re-/de-magnetization processes can be effectively reduced without sacrificing the realization of re-/de-magnetization.(4)The improvement of current trajectory has a more significant impact on the demagnetization operation over the re-magnetization operation.This can lead to the peak value of the required phase voltage appearing in the recovery stage,thus causing the failure of demagnetization operation.Therefore,the selection of the duration of current pulse trajectory must consider the voltage allowance.