Research on Current Limiting Method Used for Short Circuit Fault Current of Resonant DC Transformer Based on Inverted Displacement Phase Control

Chaoran Zhuo,Xu Yang,Xiong Zhang,Xiaotian Zhang

doi:10.1109/access.2020.3014235

Abstract

Due to the characteristics of high efficiency and flexible transformation ratio, full-bridge CLLC resonant DC transformers have been increasingly used for DC grid in recent years. Based on the analysis of the working principle of CLLC resonant DC transformer circuit, this article analysis the current gain characteristics by using fundamental wave analysis method, the parameter influences of resonance network frequency and the transformer gain is also being concerned. On the basis of using soft switching method, this article will introduce a method of inverted displacement phase control. The working range will be further refined in the original circuit, and the linear control region will be expanded as well. In this way, the output current will have a precise control under the condition of short circuit, which will satisfy the low voltage ride-through requirements of DC transformers applied to the grid connection of renewable energy. Finally, the method proposed in this article is verified by simulation and hardware-in-the-loop experiment.

Highlights

In recent years, DC transmission and distribution systems have attracted the attention of the industry field because of their advantages of large energy capacity, low losses and highpower supply quality [1]
There are many studies that have carried out a lot of research work on it, and many articles have studied the application of CLLC resonant converters in bidirectional DC/DC converters
PHASE VARIABLE INTEVAL AND PARAMETER OPTIMIZATION OF CLLC CIRCUIT When short-circuit fault occurs in the DC loop, because loop impedance is very small, in order to satisfy the requirement of low voltage ride though within a certain range of output current, it means that the working mode of the DC transformer has been changed from the original voltage source type into current source type and have a wide linear working space and high control accuracy. output voltage of the DC transformer is very low and has a wide degree of linear controllability

Summary

INTRODUCTION

DC transmission and distribution systems have attracted the attention of the industry field because of their advantages of large energy capacity, low losses and highpower supply quality [1]. PHASE VARIABLE INTEVAL AND PARAMETER OPTIMIZATION OF CLLC CIRCUIT When short-circuit fault occurs in the DC loop, because loop impedance is very small, in order to satisfy the requirement of low voltage ride though within a certain range of output current, it means that the working mode of the DC transformer has been changed from the original voltage source type into current source type and have a wide linear working space and high control accuracy. Linearly of the output current gradually deteriorates with the increase of the lagging angle β, the linear workspace of conduction angle α is within a certain range, in order to achieve a good control effect, the three quantities must be coordinated very well Another advantage of introducing inverted displacement phase control is the voltage stress reduction of switches when compare with traditional control strategy. MATHEMATICAL MODEL OF THE RESONANT CONVERTER IN CURRENT OPERATION MODE The circuit structure of the resonant converter is shown in Figure 2, the equivalent circuit diagram can be made when it starts to work in current source mode by combing with its working principle and usage of T-type equivalent circuit model (see Figure 7)

RESEARCH ON TRANSFORMER OUTPUT CURRENT LIMIT CONTROL METHOD

OUTPUT CURRENT REVERSE CONTROL METHOD

SIMULATION AND EXPERIMENTAL VERIFICATION

Findings

CONCLUSION