Research On Unified Design And Dynamic Performance Improvement For Induction Motor Field-weakening Control

Induction motors(IMs)have been widely used in high-speed applications due to the advantages of simple structure,high reliability,strong robustness,and strong field-weakening speed extension capability.The typical high-speed IM applications include CNC machine tools,electric vehicles,rail transit,and so on.At present,the industry has put forward more stringent requirements on the production process and work efficiency.High-precision and high-performance field-weakening control technology has become a key national strategic technology.To improve the system performance,this paper studies unified design and dynamic performance improvement for IM field-weakening control.The specific contents are as follows:First,this paper studies the voltage closed-loop field-weakening scheme(VCFS).IM mathematical model is established.Then,the field-weakening control equation is derived under multiple constraints.To achieve the maximum torque output,the optimal voltage and current vector trajectory in the full speed range is derived.Based on the indirect rotor field-oriented vector control system,the field-weakening controllers are set to satisfy the multiple constraints in voltage form for field-weakening control.On this basis,this paper analyses the traditional complex vector current controller and field-weakening controller.The experimental results prove that VCFS has high-torque and high-speed system response capability.Second,this paper proposed a speed-adaptive voltage closed-loop field-weakening control for IM drives.In this way,the complicated debugging work in the trial and error method is avoided.The structure of the cascade outer voltage loop and inner current loop is analyzed.Then,the voltage reference and feedback are reset to improve the field-weakening control structure.Thus,the dq-axis voltage closed-loops are established and simplified.According to the frequency-domain correction,the field-weakening controllers are designed.The experimental results confirm the investigated algorithm can improve the system dynamic performance and static performance.Further,to solve the inherent cross-coupling problems in VCFS,this paper proposes a unified design for field-weakening control based on complex vector theory.The inherent cross-coupling problems in VCFS are analyzed.The main idea of the unified design is obtained for field-weakening control.Then,this paper presents the complex vector voltage closed-loop to unify the inner current and outer voltage loops,which solves the inherent cross-coupling problem.According to the zero-pole graph and Bode diagram,the characteristic of the controlled plant is analyzed.Moreover,the field-weakening controller is designed.The experimental results confirm that the investigated method can improve the dynamic and static performance with reduced voltage overshoot and current ripple in the field-weakening region.Finally,the output voltage capability of the inverter is limited in the field-weakening region,resulting in poor current dynamic performance.To address this problem,this paper proposes an angle compensation-based voltage redistribution method.The voltage saturation problem is analyzed in the field-weakening region,which reveals that the d-axis stator voltage margin is a necessary condition to improve the current dynamic performance.Then,an angle compensation strategy for inverter output voltage is proposed,which converts the traditional two-degree-of-freedom control of the voltage amplitude and phase to the single-degree-of-freedom phase control.The proposed method redistributes the stator voltage components,increases the d-axis stator voltage margin,and improves the current dynamic regulation ability in the field-weakening region.The experimental results confirm the effectiveness of the investigated method.