Research On Strategy For Multi-constrained High-speed Flux-weakening Control Of Induction Motor Under Harsh Conditions

High-precision industrial applications place stringent requirements on the production process and efficiency of CNC machine tools.The core technology is the “high-speed and ultra-high-speed” spindle drive.The induction motor has the advantages of mature structure,wide speed range,high reliability and strong overload capability,and has been widely used in the drive system of CNC machine tools.However,the application requirements under harsh conditions,the multiple constraints within the high-speed control system,and the multi-variable,nonlinear,and strong coupling characteristics of the induction motor itself have resulted in many technical difficulties in high-speed control technology.This paper discusses the multiple constraints(maximum voltage limit,maximum current limit,and maximum slip limit)of high-speed operation of the induction motor,focusing on three key technologies: system dynamic response enhancement,maximum torque improvement,and ultra-high-speed stable operation.The ultimate task is to achieve the maximized torque,high dynamic performance and stable operation during the whole wide speed range even under complex and demandin g conditions.First,the current regulation and distribution of high-speed operation with multiple constraints are discussed.As the two basic elements for ensuring the high-speed operation capability,the current regulator design needs to take into account various factors such as decoupling,back EMF compensation,anti-integral saturation,discretization accuracy,and delay compensation;the current distribution needs a design of voltage closed-loop flux-weakening control strategy to form ideal voltage and current vector trajectories for the maximum torque.This paper analyzes,integrates,and summarizes the above points,completing the design and simulation of an optimized PI-type current regulator and the required flux-weakening controller.Secondly,to clarify the dynamic problem of the flux-weakening system caused by the Windup phenomenon,the system is abstracted as a “multiple Windup nesting” model.The inconsistency of the three voltage boundaries: voltage reference in flux-weakening controller,Anti-windup limit in current regulator and the voltage constraint in SVPWM,is analyzed,and the consistency design guideline is concluded.Then,for a certain type of operating conditions with drasti c changes in back-EMF,Windup-induced transition current fluctuations in transition period is investigated.After a systematic analysis,and summarizing t he law of settlement,a self-locking limit structure is proposed.The direct control of the voltage vector and the redistribution of the voltage margin effectively alleviate the above-mentioned dynamic problems.The feasibility of the proposed algorithm is given with experimental verification.After that,the expansion of the limit torque is achieved by high-speed operation in voltage extension region.Since there has not been a clear analysis of the relationship between voltage extension and maximum torque improvement in existing literatures,this paper proposes a universal quantitative torque analysis in voltage extension region,clarifying the relationship among voltage expansion,maximum torque,and the brought torque ripple.Further analysis on the dynamic performance is given under the two types of specific conditions: high-speed step brake with DC-Link overvoltage and sudden load change under high-speed operation.Based on the above analysis,an operating point selection flux-weakening controller is proposed.The controller can balance the suppression of torque ripple while achieving the maximum torque expansion,and at the same time,has good robustness and DC-Link overvoltage rejection.The comparison experiment is given to verify its superiority.Finally,the control strategy in the deep flux-weakening region is studied in order to broaden the speed range to the ultra-high speed region.The existing voltage and current control methods are compared and their equivalence is proved.The theoretical maximum torque point of the deep flux-weakening region considering the effect of the stator resistance is deduced to further extract its limited torque output capability.The complex vector decoupling part of d-axis current regulator is first applied as a flux-weakening path for closed-loop control,and thus a single-current decoupled path closed-loop regulator structure is proposed.While achieving closed-loop control,it eliminates an additional PI controller and parameter tuning process.The relevant verification is completed via simulation and experiments.Further,the whole algorithm is additionally realized on the platform with a 24,000 rpm high-speed spindle servo induction motor.A comparison test is given between the proposed scheme and the high-speed algorithm embedded in the OPDE-V032 A series inverter of the world’s leading TDE Inc.It is verified that the high-speed step acceleration/ deceleration performance of the proposed algorithm can be equivalent to the international advanced level.