| With the continuous development of modern rail transit technology,it is of great significance for high-speed trains to achieve the goal of high power density and lightweight.At this stage,the single-phase grid power supply system used in rail transit will inevitably cause voltage secondary pulsation in the middle DC link of the traction system.The pulsation is usually eliminated by paralleling the passive LC resonant branch on the DC side.However,this method greatly increases the volume,weight and production cost of the traction converter.In line with the trend of modern rail transit development,the elimination of the secondary resonance has been a hot topic of research.Based on the hybrid EMU project,this paper studies the functional composite traction converter without LC resonance.The goal of the paper is to drive the energy storage battery of the energy storage system and remove the secondary resonance.The function is to effectively suppress the secondary pulsation of the intermediate DC voltage,and realize the integration of the bidirectional DC/DC function and the APF function.In the aspect of power decoupling,the topology and control methods of Active Power Decoupling Circuit(APDC),which may be applied to hybrid traction converters,are summarized.Finally,Buck type APDC is selected.This solution requires only the addition of additional small-capacity DC filter capacitors for the integration of the two functions.For the part of bi-directional DC/DC control strategy,the bi-directional Buck/Boost is selected as the main circuit topology according to the functional requirements of the hybrid power system.Using the state space averaging method,a double closed-loop control system based on the average current control mode is designed,which consists of an outer loop of intermediate DC voltage and an inner loop of battery current.Aiming at the complexity of train operation and the insufficiency of dynamic response ability of existing control modes,a load power feedforward control is introduced to carry out active correction on the basis of traditional double closed-loop control strategy.For the part of DC active power filter(APF),the working principle of the filter circuit and the parameter design method of the actual capacitor voltage fluctuation are introduced,and the parameter selection index of the compensation performance optimization is given.The direct current control scheme is selected,and the hardware+software filtering method is designed to obtain the secondary current instruction.Most of the existing control strategies are suitable for low-voltage,low-power and high switching frequency occasions.The current tracking control technology of this paper adopts current closed-loop control based on quasi-proportional resonance controller(PR);The storage capacitor voltage control technology uses a double closed loop control based on the PI controller.This control strategy maintains the consistency of the power levels of the two functions with the switching frequency(1 kHz).The inductor current operates in continuous mode.Impedance analysis in the frequency domain shows that the APF has zero input impedance characteristics at twice the power frequency and an approximately open high input impedance at the low frequency band.With the help of MATLAB/Simulink software for simulation verification,the feasibility and validity of the above theory are proved by the experimental research based on the prototype vehicle experiment and the traction converter ground test platform.Figures:80,Tables:5,References:61... |
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