The Study Of Flux-Weakening Control On Three Phase Asynchronous Motor

Three-phase asynchronous motor controller is widely used in electric vehicle drive field.With the popularization of new energy vehicles,the requirements of motor controller such as flux-weakening performance,steady-state precision,dynamic response and so on are getting higher and higher.It is impossible to obtain high torque performance and small torque ripple at the same time when the voltage extension region of asynchronous motor is controlled by flux-weakening.There are still two problems in the voltage extension region: torque ripple due to overmodulation and dynamic performance degradation due to insufficient voltage margin.The flux-weakening field control is usually realized by reducing the flux linkage of the asynchronous motor.The control system of this paper is based on the vector control of rotor flux-weakening orientation,and the flux-weakening field control part of asynchronous motor is analyzed and discussed in detail.In this paper,several different research schemes are put forward to solve the problem of flux-weakening control.The vector control theory of induction motor control system is briefly introduced.The derivation of coordinate transformation is described in detail.The simplified processing of the motor equation model in vector control makes it easier to study and analyze the obtained motor model.As we all know,the dynamic mathematical model of asynchronous motor is complex.It is necessary to simplify the model so that the precise control of the motor can be realized well.The control system of this paper is based on the vector control of rotor flux field orientation,and the flux-weakening field control part of asynchronous motor is analyzed and discussed in detail.The operating state of the motor is mainly limited by the bus voltage of the inverter and the maximum current that the inverter can bear,so the speed regulation of the asynchronous motor is affected by such constraints.Therefore,it is necessary to carry out relevant technical control,so that the running state of the motor is limited in a limited range,and it can also meet the output demand of torque and rotational speed at the same time.Then,when the motor is running in the voltage extension region,the torque of themotor is analyzed when the voltage vector changes.The voltage extension region is a region surrounded by a SVPWM hexagon,a voltage limit circle and a current limit ellipse in a rotating coordinate system(dq synchronous coordinate system),which is composed of a regular hexagon,a voltage limit circle and a current limit ellipse.When the voltage vector changes with the speed,the torque dynamic performance.The variation of torque in the voltage extension region can be obtained by graphic analysis.Based on the analysis of torque variation,a novel flux-weakening control strategy for direct construction of reference voltage is proposed.The phase of the reference voltage vector of the strategy follows the phase of the given voltage vector completely,and its amplitude is reconstructed to fully follow the change of the SVPWM positive hexagonal boundary voltage,so that the output torque value meets the requirement of maximization.But the torque ripple is also large.In order to solve this problem,an integrated scheme is proposed,which combines the new strategy with the voltage margin weak magnetic control scheme.In order to optimize torque output performance,voltage margin parameters should be adjusted to find the phase point.Aiming at torque maximization,the dynamic limiting boundary of torque current is found by analyzing the relationship between torque current and excitation current in different control regions.