Research On Key Technology In Torque Controlled Induction Motor Drives Based On Indirect Field Oriented Control Method

Induction motor is widely used in electric vehicle(EV),wind power generation system due to its high reliability and low cost.Benefiting from its steady-state accuracy and dynamic performance,the indirect field oriented control(IFOC)method also finds wide applications.Despite the IFOC method has grown to maturity,higher performace and reliability of the motor drive is required in various applications.Meanwhile,there are still some difficulties and challenges in high-performance vector control method.In order to improve the accuracy and reliability of the torque-controlled drive,three subjects including flux estimation,online identification of rotor time constant and speed sensorless control are focused on in this paper.Voltage model is the simplest flux observer,but it has a well-known problem of pure integration.Despite the DC component in the stator back electromotive force can be eliminated and high-frequency nosie can be suppresed with band-pass filter based scheme,the dynamic performance of the estimation system still needs to be improved.In this paper,the band-pass filter scheme is described by complex vector analysis method.Then the optimization implementation strategy and parameter design method of band-pass filter scheme are proposed.Based on the estimated flux,a closed-loop torque control system is established to improve the control accuracy of the torque.The dot product of stator currents and rotor flux,torque,d-axis stator voltage can be chosen to form a model reference adaptive system(MRAS)to achieve the updating of the rotor time constant in an induction motor drive.However,the selection of the adaptation proportional-integral(PI)gains in the MRAS lacks theoretical basis and the stability of such a system is still not clarified.Threfore,an improved torque based MRAS is proposed through a simple modification of the traditional reference torque model.With the proposed method,the false EP is naturally avoided in practice.The information of stator frequency and torque current is incorporated into d-axis stator voltage model to expand tis effective range.Moreover,the effect of the PI gains in the MRAS on the updating process is analyzed,supplying the theoretical basis for further optimization of the adaptation gains.There is an algebraic loop in IFOC method based statically compensated voltage model for speed sensorless control.A low-pass filter is usually appled to solve this problem.In this paper,it is found out that inappropriate selection of the cut-off frequency in the LPF would result in instabililty.Threfore,adaptive design strategy of this parameter is proposed to confirm the stable operation.Besides,the influence of detuned stator resistance on the stability of speed sensorless control system is analyzed in detail.