Abstract：For permanent magnet synchronous machines (PMSMs), the speed operation range can hardly be extended due to the increasing back electromotive force and the limited DC link voltage. The flux-weakening method is employed to extend the speed operation range and maximize the torque capability. Based on the conventional current vector control system, the flux-weakening control methods can be achieved in both feedforward and feedback manners. Compared to the feedforward type flux-weakening control method, the feedback type flux-weakening control method is simple and more robust in performance against parameter mismatches. For feedback type flux-weakening control, there are two main control methods, i.e., dq-axis current-based feedback flux-weakening control (DQFFC) and current amplitude and angle-based feedback flux-weakening control (CAAFFC), which are considered to be equivalent to each other. In this paper, the system stabilities of the two methods are comparatively studied by considering maximum torque per voltage (MTPV) control and over-modulation, and the control parameter design for DQFFC and CAAFFC is discussed. In this paper, based on the current vector control system, the basic principles of the two feedback-type flux-weakening methods are introduced, and the operation modes and regions of the two flux-weakening control methods are defined and illustrated. Secondly, the voltage feedback control loops of DQFFC and CAAFFC are generalized and linearized, and the corresponding transfer functions are derived. Thirdly, based on the derived transfer function, the stability characteristics of the two flux-weakening control methods are analyzed by applying the Routh stability criterion. In the analysis, the stabilities of the two flux-weakening control methods at different operation regions are compared and illustrated from the perspective of d- and q-axis current regulations. Based on the stability analysis, control parameters for DQFFC and CAAFFC are designed, respectively. The analysis indicates that DQFFC and CAAFFC show different regional stability characteristics. Moreover, it is found that the instabilities can be caused by not only the control parameters of flux-weakening control methods but also the flux-weakening control methods inherently. From both the theoretical analysis and experiment results, it can be confirmed that the instability characteristics can be different between these two flux-weakening control methods in two different operation regions. Firstly, when the current approaches the MTPV curve, the DQFFC method has a weak voltage regulation capability since only the d-axis current can be regulated. The current can be prevented from moving inside the voltage limit circle, causing oscillation in over-modulation. On the other hand, the CAAFFC method mainly regulates the q-axis current in this region, allowing the current to move within the voltage limit circle. Thus, the oscillation can be alleviated. Secondly, when the machine operates under a light load condition, the CAAFFC method mainly regulates the q-axis current, and the current cannot move inside the voltage limit circle, which causes an unstable transition between motoring and generating modes. On the other hand, DQFFC with d-axis current regulation has no issues since the current can move within the voltage limit circle. Thus, a smooth and stable transition can be achieved.
王超, 诸自强, 徐磊, 吴溪蒙. 永磁同步电机的两种反馈式弱磁控制方法的稳定性比较研究[J]. 电工技术学报, 2023, 38(14): 3689-3707.
Wang Chao, Zhu Ziqiang, Xu Lei, Wu Ximeng. Comparative Stability Study of Two Feedback Flux-Weakening Control Methods of Permanent Magnet Synchronous Machine. Transactions of China Electrotechnical Society, 2023, 38(14): 3689-3707.
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