Induction Motor Operation And Control Of Field-Weakening With High Multiplication Factor

In many applications,such as CNC machine tools,electric vehicles,and flywheelbattery energy storage,high speed induction motor is appropriate which has characteristics of simple structure,high reliability,strong overload capacity and no back electromotive force in free rotation.Volume and cost can be effectively reduced when induction motor possesses high speed performance by field-weakening operation.Parameter identification of induction motor,field-weakening control algorithm,speed estimation and optimization design of controllers are significant challenges to realization of the field-weakening control.Therefore,induction motor operation and control of field-weakening with high multiplication factor is studied in this paper,and it mainly includes the following several aspects.1.Regarding to induction motor speed regulation system of field-weakening with high multiplication factor and considering lots of inherent nonlinear factors,a parameter identification method for induction motor featuring high precision,good robustness and strong versatility is proposed.In the identification process,output voltage of inverter is usually obtained by reconstruction.However,the actual voltage has errors due to the nonlinear factors of inverter such as dead zone,on-off delay and forward voltage drop.Consequently,identification precision of the motor parameters is not satisfied.To solve this problem,an identification method using mixed excitation signal with DC bias for rotor resistance and leakage inductance is proposed.In addition,considering magnetic saturation for field-weakening operation of induction motor,magnetizing curve can be obtained by the proposed method.2.Based on stator flux orientation,the control algorithm of torque-maximizing field-weakening with high multiplication factor for induction motor is proposed.Considering limitations of voltage,current and torque of induction motor,the optimal operating points of constant torque region,field-weakening region I and field-weakening region II are analyzed for torque-maximizing.Then,the field-weakening with high multiplication factor control algorithm,which has low dependence on motor parameters and smooth transition between different operation regions,is proposed based on the analysis.Comparing to traditional‘1/ω_r method’and‘optimal model method’,simulation experiments for field-weakening with multiplication factor of 5 are conducted.Eventually,the feasibility of optimal field-weakening control for induction motor is verified.3.Towards speed sensorless control of field-weakening with high multiplication factor for induction motor,the speed estimation method based on model reference adaptive system is proposed.Low-pass filter used for flux observation in traditional method has poor performance at zero or very low speed and influences convergence of the estimated due to the filter’s inherent delay.By comparison,the proposed method which adopts model reference adaptive system with full-order flux observer can improve system performance effectively.For the discrete full-order flux observer design of field-weakening with high multiplication factor in practical application,a discretization method based on Taylor series is proposed.Comparing to forward Euler method and bilinear transformation method,the proposed method has better comprehensive performance at several aspects such as observation error,calculation time and stability of the discrete-time observer.Meanwhile,for possible requirement of starting a free-running motor,considering the impact of transient current which is caused by mismatch between output frequency of inverter and rotor frequency,an off-line speed estimation method is also proposed to achieve fast and stable start-up of the motor.4.Regarding to controller parameters optimization of field-weakening with high multiplication factor for induction motor,this paper proposes an on-line optimization method for parameter adaptation controller.On the condition of field-weakening with high multiplication factor,flux variation induces strong nonlinear characteristics between torque and current.Influence on the speed control performance from controller parameters of different operation region is analyzed.Moreover,an on-line optimization method for parameter adaptation controller of field-weakening with high multiplication factor is proposed.The proposed method considers nonlinear influence of field-weakening with high multiplication factor,and achieves well dynamic and steady performance during the whole speed region.