An Improved Feedback Linearization Control Strategy for High-Speed Railway Traction Converters
Yu Wenqian1, Liu Zhigang1, Zhang Yougang1, Gou Jing2, Liu Jiawei2
1. College of Electrical Engineering Southwest Jiaotong University Chengdu 610031 China; 2. State Grid Sichuan Economic Research Institute Chengdu 610041 China
Abstract：In the traditional control mode adopted in the vehicle-grid system, the AC side voltage sensor is used to measure the AC side voltage to obtain the phase information for coordinate transformation and the voltage amplitude of the AC side. In order to reduce the risk of instability caused by sensor faults and reduce the influence of AC side voltage fluctuation on the system, a feedback linearized virtual inertia control (VIC) strategy based on virtual flux and sliding mode observer (SMO) is proposed. Referring to the concept of flux in AC motor, the integrator of traditional virtual flux observer (VFO) used in rectifier is analyzed. It is pointed out that the existing integrator is easily affected by the initial value of integration and the amount of DC bias, and the integrated signal contains a large harmonic component. An improved integrator is proposed by concatenating a second-order low-pass filter followed by a band-pass filter. The gain selection in the proposed integrator is theoretically analyzed using the Bode diagram and unit step response curve, the value of the gain is determined, and the new VFO is obtained. Using the virtual flux estimate obtained by VFO and voltage reconstruction calculation, the amplitude and phase information of AC side voltage needed for coordinate change can be obtained. Then, the control mode without a voltage sensor is realized by combining with the current inner loop control part of feedback linearized VIC based on SMO. The results of Matlab/Simulink simulation and hardware in-loop experiments show that the improved integrator can eliminate the uncertainty of the initial value of integration and the adverse effects caused by DC voltage bias. Because of the addition of a band-pass filter, it can filter the low-frequency and high-frequency clutter except for the fundamental signal. Compared with the traditional dq decoupling control and the feedback linearized VIC based on SMO control, the proposed control strategy has the largest critical value of the grid side inductance. Under the same circuit conditions, the low-frequency oscillation (LFO) phenomenon will not occur, and the DC voltage offset phenomenon will not occur before reaching the critical value. The response time of the grid side inductance mutation is the shortest, and the voltage fluctuation is the least. In the dual simulation experiment, the proposed improved control mode has the slightest fluctuation of output voltage and the shortest response time when the load suddenly increases or decreases. It can be further found that the estimated DC-side current of SMO output is closer to the theoretical value than that of the control method with a grid voltage sensor. In the multi-vehicle simulation, the LFO phenomenon can be suppressed compared with dq decoupling control, and the response time and DC voltage fluctuation can be reduced. In addition, the number of sensors can be greatly reduced compared with the control mode of network pressure sensors. The proposed control method enhances the robustness of the vehicle-grid system, reduces the influence of external interference on the vehicle-grid system, and saves the hardware cost of the controller.
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2023, Vol. 38 
