Research On Resonance DC-DC Topology And Control Strategy Of 10kV Power Electronic Transformer

The traditional distribution network is mainly based on the AC distribution network.But with the rapid economic growth,the type of load in the distribution network is becoming more and more diversified.The proportion of data center,electric vehicle and other DC load is growing.Further more,the permeability of the distributed power supply is getting higher and higher,and a part of the distributed power supply is DC.In the existing distribution network,DC distributed power supply is usually accessed by converting into AC and then connecting to the grid,and the efficiency is low.So it is difficult when the traditional AC transformer is used in the distributed network.At the same time,due to the access of distributed power and energy storage devices,the direction of the power flow in distribution network is transformed from one-way to two-way flow,it is difficult for traditional power transformers to control the power flow.Because of the high voltage level in the distribution network,the switch tube of DC/DC converter can not withstand the voltage level.Therefore,the technology of transformer in DC power distribution network has been a hot research topic.This paper is based on the state grid technology projects "10k V power electronic transformer key technology research".And the following studies were carried out.(1)The topology of the current DC-DC converter and its advantages and disadvantages are analyzed.(2)The working principle and mathematical model of the resonant CLLC DC-DC converter are studied.The relationship between the K(ratio of the excitation inductance and the resonant inductance),the switching frequency and the topology voltage gain is derived,and the relationship between output load,switching frequency and topology voltage gain is also derived.The influence of the circuit parameters on the characteristics of CLLC DC-DC converter is obtained.(3)The control strategy of CLLC resonant DC DC converter is studied.By deducing the expression of the transmission power of the CLLC resonant DC-DC converter,the influence of the phase shift angle on the transmission power is obtained.(4)Based on the cascaded CLLC resonant DC DC converter used in high voltage and large capacity,the power balance control strategy and the power flow control are studied.(5)Based on the research of the topology parameters and control strategy,the corresponding simulation model is built in the simulation software PSCAD,and the correctness of the design parameters and the control strategy are verified by simulation analysis.