Sensorless Control Strategies For Traction Induction Motors Applied In Railway Vehicles

Speed sensorless control is one of the key technologies of railway traction control,and its application helps to improve the reliability of the traction systems and reduce the maintenance cost.This dissertation aims at the problems of speed sensorless control for traction induction motors in railway vehicles.In-depth theoretical analysis and research are carried out on the speed estimation based on full-order adaptive observer,the restarting strategy of free-running induction motors under sensorless control,and the improvement of speed estimation performance in low speed region.An improved speed estimation strategy based on full-order adaptive observer is proposed.First,the numerical instability problem in high speed region by using traditional discrete method due to low switching frequency is analyzed,and an improved full-order discrete model is proposed to avoid this problem.By discretizing stator current and rotor flux equations in different reference frames,the stability of 27 discrete combinations is analyzed,and the appropriate discretization method is selected by analyzing the difficulty of digital implementation from six stable combinations.Next,the feedback gain matrix is designed in discrete domain,and the speed estimation is realized in the synchronous rotating reference frame.Based on the improved speed estimation strategy,the stability of the improved full-order adaptive observer is analyzed.First,the transfer function between current error and speed estimation error is established in the synchronous rotating reference frame,and the stability conditions are analyzed according to the Jury criterion.Next,the parameter sensitivity of the full-order adaptive observer is analyzed,the sensitivity analysis mathematical model is established based on the discrete observer model combined with the continuous motor model,and the influence of parameter variation on the speed estimation is analyzed one by one.Base on dual current closed-loop DC injection,a fast restarting strategy of restarting free-running induction motor under sensorless control is proposed.First,the characteristics of rotating electrical machines in the case of short-term power interruption are analyzed.A mathematical model of rotating electric machine with single current closed loop DC injection is established,and a method for estimating speed by measuring feedback current frequency is analyzed.Next,a strategy for speed identification based on dual current closed-loop DC injection is proposed,and a mathematical analysis model of the motor under DC injection is established.A voltage model flux observer is designed to obtain the rotor flux information,the DC offset and the noises are eliminated by a three-order band-pass filter,and a subsequent normalization is used to obtain the flux signals with unified amplitude.The normalized flux signals are then used with the phase-locked loop designed to obtain the initial estimated speed.Last,the proposed restarting procedure is composed of three steps.During the initial step,the speed is estimated by DC current injection-based method.In the next step,the speed estimation is further refined while the torque is regulated at zero and machine's flux is reestablished.The final step smoothly restores the normal operation of the motor and uses the full-order adaptive observer for speed-sensorless vector control operation.Based on the unstable phenomenon of sensorless control in low speed region under regenerative brake mode,an improvement strategy of speed estimation performance is proposed.First,the mechanism of unstable speed estimation in low speed region under regenerative brake mode is analyzed,and the unstable boundaries are determined.The improved speed estimation mechanism is proposed,and the key parameter is designed.The improved speed estimation stability is verified by the zero-pole analysis of error transfer function.Next,the stator resistance and rotor resistance identification strategy for induction motor is designed.A stator resistance identification strategy is proposed which works independently during the DC current injection step of restarting procedure.The stator resistance identification works simultaneously with the speed estimation,and the stator resistance identification value and the initial motor speed are obtained by the end of the DC current injection.Last,the strategy of high-frequency current injection to obtain the equivalent resistance of the motor is designed.The parameter identification coordination logic is proposed,and the identification strategy of rotor resistance is realized.A large number of simulations are carried out based on traction control model,and experimental results are completed based on experimental metro traction system and Typhoon hardware-in-loop simulation.The feasibility and effectiveness of the above speed sensorless control strategies are verified.120 figures,10 tables,165 references.