Control of the Distributed Hybrid Energy Storage System Considering the Equivalent SOC

Wei Jiang,Zhiqi Xu,Saifur Rahman,Yifan Deng,Kai Ren,Ke Sun,Bin Yu

doi:10.3389/fenrg.2021.722606

Abstract

A hybrid energy storage system (HESS) consists of two or more types of energy storage components and the power electronics circuit to connect them. Therefore, the real-time capacity of this system highly depends on the state of the system and cannot be simply evaluated with traditional battery models. To tackle this challenge, an equivalent state of charge (ESOC) which reflects the remaining capacity of a HESS unit in a specific operation mode, is proposed in this paper. Furthermore, the proposed ESOC is applied to the control of the distributed HESS which contains several units with their own local targets. To optimally distribute the overall power target among these units, a sparse communication network-based hierarchical control framework is proposed. This framework considers the distributed control and optimal power distribution in the HESS from two aspects - the power output capability and the ESOC balance. Based on the primary droop control, the total power is allocated according to the maximum output capacity of each unit, and the secondary control is used to adjust the power from the perspective of ESOC balance. Therefore, each energy storage unit can be controlled to meet the local power demand of the microgrid. Simulation results based on MATLAB/Simulink verify the effectiveness of the application of the proposed equivalent SOC.

Highlights

Energy storage systems are widely deployed in microgrids to reduce the negative influences from the intermittency and stochasticity characteristics of distributed power sources and the load fluctuations (Rufer and Barrade, 2001; Hai Chen et al, 2010; Kim et al, 2015; Ma et al, 2015)
The equivalent SOC (ESOC) is proposed as an index to evaluate the state of charge of a hybrid energy storage system (HESS) unit considering its operation mode
A distributed control method is proposed that aims to optimize the power allocation among HESS units that are in the same microgrid

Summary

INTRODUCTION

Energy storage systems are widely deployed in microgrids to reduce the negative influences from the intermittency and stochasticity characteristics of distributed power sources and the load fluctuations (Rufer and Barrade, 2001; Hai Chen et al, 2010; Kim et al, 2015; Ma et al, 2015). 3) On the basis of variable droop coefficient control, the correction considering 〈ESOC〉 equalization is superimposed, so that the ESOC of each energy storage unit can be regulated within a reasonable range while the power of each unit is distributed once according to the proportion of the maximum output power of each unit, and the 〈ESOCi〉 of each energy storage unit tends to be consistent. This paper considers the way of changing the droop coefficient in different modes, so that the local droop control of energy storage system can be adjusted according to the maximum output active power at any time and in any mode. Where: Nip and Nii are the PI parameters of the 〈ESOC〉 regulation term corresponding to the ith energy storage unit HESSi, ESOC* is the average value of 〈ESOC〉 of the distributed energy storage system obtained by the consistent algorithm, and kpi[Z] represents the active power droop coefficient of the energy storage unit in Z mode. In 0–3 min, the Nip and Nii in Eq 24 was set

CONCLUSION

DATA AVAILABILITY STATEMENT