Research On Flexible Self-excitation Control Of Cage Induction Motor

Considering the distinct advantageous features of the sturdy structure,the simple maintenance,the continuously adjustable excitation and the short-circuit De-Excitation protection,cage induction motors have been widely used in the fields of independent power systems,such as wind power,ships,aircraft,vehicles.The switching capacitor method is usually used in the Cage induction motor self-excitation.This control method has many disadvantages,such as large volume,discontinuity and low efficiency.With the development of power electronics technology,combining the three-phase voltage-type PWM rectifiers,a type of flexible self-excitation electrical system is constituted,which will become an effective means to increase the power density of independent power systems.Flexible self-excitation electric systems are mostly used in the cases where the speed range of the prime mover varies widely and the load impact is strong,which is essentially a type of multi-variable,strongly coupled nonlinear variable parameter system.With the in-depth study of the dynamic relationship between the electromagnetic torque of the cage asynchronous generator and the physical parameters of the PWM rectifier,based on theories of space vector modulation,fractional sliding mode control,direct torque control and internal mode control,a new method of first-order sliding mode robust self-excitation control method is proposed.The new method is based on the instantaneous power balance of the power generation system.In the voltage-flux outer loop subsystem,the state variables are consists with the square terms of the rectified voltage and the flux linkage.By using the fractional sliding mode control method,the target instruction of the current inner loop subsystem is formed.The loop subsystem uses internal model control to achieve robust tracking control.In order to perform the physical test experiments,the cage-type induction motor power generation experiment platform was established.By calculating the main circuit parameters and designing the drive circuit,analog signal(voltage,current,speed)acquisition circuit and the minimum DSP system,the flexible self-excitation controller for cage induction motor based on TMS320F28335 is designed.In order to carry out the real-time simulation verification of the model algorithm,which is performed on the hardware system,and realize the expansion of the control algorithm,the hardware system,basing on model designment,was researched.The Embedded coder toolbox in MATLAB was used to automatically generate the system control code.Under the conditions of suddenly changing with the speed and the load,algorithm simulation and physical test experiments were performed.The control algorithm simulation and physical test results show that,on the load and the speed suddenly changing condition,with model uncertainties such as frequency fluctuations and physical parameter dispersion,comparing with the traditional voltage outer-current inner-loop feedforward control method,the new control method can effectively improve the response speed of magnetic flux and torque control,reduce system chattering and achieve variable-speed constant-voltage robust control in a wide operating range,and verify the feasibility of model-based hardware system development,which will be a new method for improving performance of isolated power systems(IPS).