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

Comparative Stability Study of Two Feedback Flux-Weakening Control Methods of Permanent Magnet Synchronous Machine

对于反馈式弱磁控制,通常有两种方法,即基于dq轴电流的反馈式弱磁控制(DQFFC)和基于电流幅值和角度的反馈式弱磁控制(CAAFFC),被广泛使用并被认为相互等价。该文基于最大扭矩电压比(MTPV)控制,对这两种方法的系统稳定性进行了比较研究。分析结果表明,不稳定既由控制参数设计引起,也与弱磁控制方法本身的特性有关。对于方法本身导致的不稳定,DQFFC和CAAFFC在不同的工作区域中表现出了不同的特性。基于在不同的工作区域内,该文从电流调节方向的角度来说明系统稳定和不稳定的工作机制。此外,针对DQFFC和CAAFFC在不同区域内的稳定性差异,给出了MTPV控制器的控制参数设计指南。最后,通过实验结果进行了演示和验证。

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.