Research On Light-Load Oscillation Suppression Strategies Of Variable Frequency Inverter-Driven Induction Motors

The variable frequency drive systems of induction motors under V/F control mode can achieve ideal speed performances and can be realized simply with the lower cost than other control drives, where they gains wide applications in the field of AC variable speed drives. However, when the general inverters drive induction motors running nearby the intermediate frequency band below the base frequency without load or with light load, there is a kind of phenomenon of oscillation that shows vibration of the stator current and fierce buffeting of rotational speed or torque. The unstable status of induction motor will influence the control performance of system and also endanger the security of system. In order to solve the mentioned problem above, the mechanism of the system oscillation and the related suppression strategies are studied in detail in this subject.Firstly, the theory of V/F control based on the steady-state equivalent circuit of induction motor and mathematical model under the dq coordinate are analyzed. The stability problem of induction motor running without load under the V/F control mode is studied. Through the analysis of the performance of oscillation and the results of the computation with simulation, the trends of system oscillation which influenced by the parameters of induction motor are acquired.Secondly, the essential influence of dead time to system oscillation is analyzed particularly. The method of the dead time compensation based on the correction of the duty is studied and the performance simulation of which proves that this strategy of compensation can damp oscillation and distortion of the motor current caused by the long dead time and high carrier frequency.Thirdly, in order to solve the problem of oscillation effectively, the synthetic strategy of oscillation suppression basing on the theory of instantaneous power that using the feedback of the active current oscillating components with dead time compensation is proposed. By the tool of MATLAB/Simulink, the model of system is established. The results of simulation proved that the strategy can solve the oscillation of the induction motor with effect.Finally, the tested platform of the induction motor under V/F control mode is designed. Through the experiment, it is indicated that the synthetic strategy proposed that based on the feedback of active current oscillating component with dead time compensation in this article can solve the oscillation problem of induction motor under V/F control mode. The strategy studied in this article enhances the stability of the system of traditional V/F control mode effectively.