| With the double carbon target,it is imperative to develop clean and renewable energy.For the power industry,DC microgrid has become a hot spot for research in the industry nowadays due to its advantages of simple structure,small size,no reactive power,green environment and high quality power supply.As a key part of DC microgrid,energy storage system plays a crucial role in regulating the system stability of microgrid and smoothing the fluctuation of renewable energy.However,the current single energy storage technology is difficult to take into account the demand of high power density and high energy density energy storage,which is insufficient to meet the demand of DC microgrid for energy storage system to improve power quality.Based on this,the hybrid energy storage using two or more energy storage technologies with their own advantages can achieve the purpose of more adaptable to the load and improve the reliability of power supply,and also make up for the economic shortage of a single energy storage,so its research is of great significance.This paper is based on a hybrid energy storage system for DC microgrid.With the goal of economic and reliable operation,the paper focuses on three key technologies for hybrid energy storage system port converter topology in DC microgrid,the corresponding control strategy and the optimal configuration of hybrid energy storage system capacity for in-depth research.The progress of work and the main innovations achieved in the paper are as follows.1.A three-port bidirectional full-bridge DC-DC converter connected to a DC microgrid bus with hybrid energy storage is used as the research object for system topology analysis.The conventional phase-shifted full-bridge DC-DC converter,when operating at light load,can help the over-arm switch for soft switching due to the large secondary inductance,while the lagging arm has only a small leakage inductance and line inductance for assistance,making soft switching more difficult,thus making the lagging arm more difficult to achieve soft switching than the over-arm.To address this problem,this paper uses the addition of an active auxiliary circuit to improve the topology of a three-port bidirectional full-bridge DC-DC converter to achieve soft switching of the lag arm of the power converter.The paper firstly investigates the topology of the two-port bi-directional full-bridge DC-DC converter with active auxiliary circuit,and analyzes the operating mode of the converter and the implementation of the hysteresis arm soft-switching in detail;then extends the research theory to the three-port bi-directional full-bridge DC-DC converter to realize the access of multiple energy storage devices and the implementation of the energy control strategy of the hybrid energy storage system;finally,the proposed three-port bi-directional full-bridge DC-DC converter is investigated.Finally,the proposed three-port bidirectional full-bridge DC-DC converter is analyzed and studied in terms of power transfer and decoupling control,and its feasibility is verified by simulation.2.The corresponding control strategy of the hybrid energy storage system for DC microgrid is designed based on a three-port bidirectional full-bridge DC-DC converter with active auxiliary circuit.According to the respective characteristics of hybrid energy storage technologies,a low-pass filter-based power allocation scheme and a charging and discharging protection strategy for energy storage elements are proposed from the perspective of coordinated control of hybrid energy storage power.Finally,the controller is simulated using Matlab/Simulink software,and the results show that the control strategy is feasible and reliable and achieves the purpose of maintaining the bus voltage stability.3.To address the capacity allocation problem of hybrid energy storage system for PV-DC microgrid,a power allocation method based on low-pass filter decomposition is proposed,and an improved bat algorithm is used to optimize the capacity allocation of hybrid energy storage,and a hybrid energy storage system is established with the objective of minimizing the whole life cycle cost of hybrid energy storage device and the constraints of power balance of the system,charge state of energy storage and load shortage rate.The model is used to achieve the economic optimization of the hybrid energy storage system.The simulation results show that the improved bat algorithm not only optimizes the working state of the battery and reduces the life-cycle cost of the energy storage system,but also accelerates the convergence speed. |
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