| Speed sensorless technology abandons the encoder which is expensive and difficult to maintain,and has the advantages of high reliability and low cost,so it has been widely used in industrial frequency converter.However,under the condition of limit speed operation,the stability of speed sensorless control can not meet the industrial demand,because the speed sensorless control technology can not observe the rotor speed at zero synchronous speed.Among the existing solutions: for the observer based on the non-anisotropy of the motor,the motor can achieve zero synchronous speed with load by the method of signal injection,but this method has special requirements for the design of the motor body.It can not be widely used;for the observer based on motor mathematical model,the stable operation of low synchronous speed can not be realized because of the unobservable problem of zero synchronous speed.In order to solve this problem,voltage injection is carried out in the full-order flux observer(Adaptive Full Order Observer,AFO).This method can observe the rotor speed at zero synchronous speed,but the voltage injection also brings speed error,and this method only realizes the stable operation of zero synchronous speed in the AFO model.Based on these problems,this paper carries out research.First of all,this paper analyzes the reason why the rotor speed of the induction motor AFO model is unobservable at zero synchronous speed,then explains the principle of the voltage injection method,deduces the new speed estimation law after voltage injection,and gives the calculation method of the injection coefficient.Secondly,based on the stability theory of nonlinear system,the zero synchronous speed stability of induction motor control system after voltage injection into AFO model is verified by using local weak energy theorem.In this paper,the cause of speed error is analyzed,and a strategy of using feedback matrix coefficient to reduce speed error is put forward.In order to verify the generality of the voltage injection method,based on the model reference adaptive(Model Reference Adaptation of Back Electromotive Force,EMF-MRAS),this paper analyzes the reason why the rotor speed of the induction motor based on EMF-MRAS is unobservable at zero synchronous speed,and introduces the voltage injection method to realize the stable load operation of the induction motor vector control system based on EMF-MRAS at zero synchronous speed.Finally,the correctness of the theory is verified by experiments. |
