Research On Input Stage Rectifier Control Strategy For Locomotive Power Electronic Transformer

The high-speed development of electric locomotives puts forward new requirements for the operation of electric locomotives.To improve the running speed of electric locomotives,transformers with larger capacity are needed to provide output power.Therefore,it is one of the feasible methods to develop large-capacity and small-sized transformers.Compared with the traditional transformer,the power electronic transformer has the advantages of small size,light weight,controllable voltage and current and power factors of the primary and secondary sides,various power supply forms and open circuit protection communication,and has become one of the research hotspots of locomotive lightweight.The main structure of the power electronic transformer can be divided into an input stage,an isolation stage and an output stage three-stage structure.The paper analyzes the topology characteristics of the input stage and the isolation stage.At the same time,combined with the single-phase high-voltage power supply characteristics of the electric locomotive,the input stage cascaded H-bridge structure and the isolation-level independent core structure are determined,and the electric locomotive power is given.The overall topology of the electronic transformer.In the operation of power electronic transformers,the stable DC voltage given by the input stage rectification has an important influence on the transformation of the latter stage.In order to reduce the pollution of the harmonics to the grid and the stability of the DC voltage on the output side,the paper studies the control strategy,modulation mode and DC-side voltage balance strategy of the input stage.When the load changes,the adjustment is performed faster,and the nonlinear sliding mode variable structure controller is designed in the voltage outer ring to ensure the output current stable reference value;in the current inner ring,the active component and the reactive power are respectively controlled by current decoupling.The component reduces the number of adjustments of the parameters;the modulation mode selects the carrier phase shift modulation technology,which not only facilitates the expansion of the module but also increases the level,so that the input side voltage is sinusoidal;to ensure the balance of the DC side capacitor voltage,the voltage component is superimposed.The method adjusts the individual modules separately,speeding up the adjustment speed.In order to verify the feasibility and effectiveness of the proposedstrategy,the MATLAB simulation platform was built to analyze the results.The results show that the sliding mode variable structure control strategy is compared with the PI control strategy.The output DC voltage is closer to the expected value,and the power factor is also better.High,improving the efficiency of power utilization.