Research On Voltage-Torque Extension Scheme Of Induction Motor In Field-weakening Region

As a national key strategic technology,high-speed machining represents the level of industrial automation in China and is of great significance to industrial transformation and upgrading.Induction motors are widely used in high-speed machining due to their high reliability,economy,and strong field-weakening speed extension capability.Nowadays,high-precision industrial applications require more stringent production processes and efficiencies.Not only do spindle drive systems require extremely high speed operation,but also key technical indicators such as step acceleration and braking times,dynamic control,high-speed loading,and sensorless control.Higher requirements have been put forward,which has led to the limitations of the existing induction motor field-weakening theory in high-end manufacturing industry.In this paper,the field-weakening control mechanism of induction motor is deeply explored.Based on the maximum torque theory,the inherent relationship between voltage expansion and torque extension is revealed.The dynamic performance,the maximum loading capacity,and the current control performance are optimized.Meanwhile,the high robustness of the system is maintained.The specific contents of the paper are as follows:Firstly,the maximum voltage,maximum current,and maximum slip frequency constrains in field-weakening region are studied in this paper.The voltage and current vector trajectories are derived.Along the trajectories,the maximum torque output can be realized in theory.To control the voltage and current vector move along the theoretical trajectories,the voltage closed-loop is introduced to the traditional induction control system.The advantages and disadvantages of the voltage closed-loop field-weakening method and the traditional“1/?_r”method are analyzed and compared by simulation experiments.The results show that the voltage closed-loop method has obvious advantages in the maximum torque output and acceleration/braking performance.Further to increase the maximum torque in field-weakening region,the voltage utilization of the traditional inscribed circle voltage is extended to hexagon.And then the piecewise linear region can be fully used under hexagon voltage.Then,the voltage loop and the field orientation are regarded as a whole section.Based on this assumption,the following conclusion can be drawn:the independence control of the voltage amplitude and voltage phase is the necessary condition for accurate controlling of the voltage vector.Based on this analysis,the coupling mechanism of voltage vector amplitude and phase in traditional hexagon method is revealed.And the time-phase delay can be caused by the amplitude-phase coupling,which leads to the absence of hexagonal apex voltage.To solve problem,a standard hexagonal voltage output strategy without phase delay is proposed in this paper.By introducing the overmodulation one-region algorithm,a whole hexagonal voltage is realized in field-weakening region.The correctness of the theory and the effectiveness of the optimization algorithm are analyzed and verified by experiments.After that,on the basis of the hexagonal voltage,the six-step operation is introduced to the system for extreme torque extension.And the overmodulation two-region algorithm is combined to the SVPWM module.In order to analyze the relationship between voltage nonlinear expansion and torque extension under six-step operation,a new equivalent circuit of induction motor in synchronous rotating coordinate system is proposed according to the voltage vector jump rule in d-q frame.The effectiveness of the torque extension in six-step mode is confirmed by the quantitative analysis of torque extension and torque ripple.The relationship between the original current loop and the newly harmonic loop is analyzed independently.To cut off the main current harmonic(6th harmonic),a second-order generalized integrator(SOGI)-based band-stop filter is designed for the feedback current in the current loop.The designed filter can achieve IM stable operation in six-step mode without effecting the bandwidth of the current loop.Finally,the improvement of the system and the filtering effectiveness of the designed filter are verified by comparison experiments.Finally,aiming at the degradation of current dynamic performance in six-step mode,the relation between voltage margin and dynamic current control is analyzed according to the transient voltage model of induction motor.Then,the focus is placed on the transition field-weakening region when the worst current control performance happens.The root cause of the uncontrolled current in the transition region is studied.A new nonlinear anti-windup structure is proposed.Since the anti-windup operation is finally realized by field-weakening control,the d-axis voltage margin is prior in the proposed method.Futher to achieve the sensorless control in field-weakening region,the full-order flux observer is introduced to the system.The speed adaptation rate is designed based on Lyapunov stability theory.The discrete-domain full-order flux observer is obtained through the"prediction-correction"-combined forward Euler discretization method.The experimental results show that the current control performance in the transition region is enhanced,and the sensorless algorithm is reliable under extreme conditions such as load and high speed.