Model Predictive Control Strategy for DAB-LLC Hybrid Bidirectional Converter Based on Power Distribution Balance

The DAB-LLC hybrid bidirectional converter based on Sigma structure combines the advantages of LLC resonant converter and dual active bridge converter, which has gained the attention of many scholars in recent years. However, there are few studies on the power distribution relationship of the internal sub-module, which affects the performance and efficiency of the whole system. Therefore, this brief proposes a model predictive control strategy based on power distribution balance, which firstly predicts the output by means of a discrete reduced-order model of the converter, then utilizes the constructed power distribution model to design a new cost function, and finally obtains an appropriate control quantity, so as to realize the improvement of the dynamic performance and at the same time ensure the stability of the power distribution relationship of the converter. Finally, the proposed control strategy is verified by experiments.

I. Introduction

IN recent years, energy routers have received wide attention and application in the field of distributed renewable energy generation and DC microgrid, and bidirectional isolated DC/DC converters are a key link in energy routers [1], [2], [3], [4]. With the increase of power and voltage level, the bi-directional isolated DC/DC combination converter has become a research hotspot. The bidirectional LLC resonant converter and dual active bridge converter (DAB) are the most studied [5], [6]. The LLC resonant converter has the highest efficiency when operating at a fixed resonant frequency (DCX mode), but the voltage regulation ability is insufficient. If variable frequency control is used, high circulation will be introduced when the voltage regulation range is too wide, reducing efficiency. And, DAB converter is easy to lose soft switching under light load, and high switching loss under heavy load. To sum up, they all have their shortcomings. Therefore, it can be considered to combine these two converters to form a hybrid converter. Among them, the Sigma structure-based DAB-LLC hybrid bidirectional converter has received attention from scholars worldwide [7], [8], [9], [10], [11]. By setting the transformer ratio of different submodules, the main power can be processed by the LLC circuit, and DAB uses the partial power to achieve output regulation, as shown in Fig. 1. Therefore, the DAB-LLC hybrid converter combines the high efficiency of LLC resonant converter operating in DC/DC transformer (DCX) mode and the advantages of bi-directional power flexible switching of dual active bridge converter. As conclusion, this brief takes the DAB-LLC hybrid converter as the main research object to carry out research. Fig. 1.

The structure diagram of DAB-LLC hybrid converter.