The Research On Indirect Torque Control System Of Brushless Doubly-Fed Machine

Brushless doubly-fed machine (BDFM) is a novel AC machine which can operate on asynchronous and synchronous state. It can be used in AC adjustable-speed drive systems as a motor or be used in adjustable speed constant frequency system as a generator.The BDFM system has the characteristics of no bush and less capacity inverter.it is particularly suitable for large-capacity AC variable speed drive and variable speed constant frequency wind power, hydroelectric power system.The two-axis models of cage-rotor brushless doubly-fed machine are different in many literatures. The mathematical model are analyzed and deducted and the correct mathematical model for brushless doubly-fed machine is ultimately determined in this paper.The conclusion is a solid foundation for the motor control system.Rotating coordinate transformation was required in torque observation of brushless doubly-fed machine in existing literatures.And the observating result was affected by the motor parameters and speed measurement error. Based on the correct mathematical model and the existing research results, the theoretical derivation of calculating electromagnetic torque respectively in control winding and power winding stationary reference frame is improved in this paper. Rotating coordinate transformation is avoided and control winding and power winding resistance just uesed in this method. It is possible that direct and indirect torque control of BDFM can be achieved in the stationary coordinate system. The system's structure become simple and clear.Torque ripple in conventional direct torque control(DTC) system was large at low frequencies. Control winding current and flux waveform were aberrated seriously. In order to solve this problem, copied from control theory of indirect torque control(ISC) of induction motor and combined with mathematical model, the working principle and structural characteristics of the BDFM, the control theory of ISC for BDFM and the calculating method of control winding static flux angle in this control system are proposed.To verify the feasibility of ISC system for BDFM, simulation of the control system is carried out in the MATLAB simulation environment. The simulation results show that the proposed control method is valid. Compared with the results of conventional DTC system, the results show that ISC can effectively reduce the torque ripple at low frequencies and improve the control winding current and flux waveforms. These results lay the theoretical foundation for this method applying to actualsystem.The program of ISC system of BDFM is compiled and the control system is implemented on the experiment platform based on digital signal processing chips TMS320LF2407A in this paper. Steady state and dynamic experiments were carried out at different speeds, and compared with the experiment results of DTC system of BDFM, are consistent with the simulation results.