An Enhanced Equivalent Circuit Model of Vanadium Redox Flow Battery Energy Storage Systems Considering Thermal Effects

Binyu Xiong,Qingyong Zhang,Yixin Su,Yang Li,Jinrui Tang,Yesen Yang,Zhongbao Wei

doi:10.1109/access.2019.2952212

Abstract

Thermal issue is one of the major concerns for safe, reliable, and efficient operation of the vanadium redox flow battery (VRB) energy storage systems. During the design of the operational strategy for a grid-connected VRB system, a suitable mathematical model is needed to predict the dynamic behaviors under various operating conditions. However, conventional VRB models usually neglect the impact of temperature variations on system performance. This work develops an enhanced VRB model with the consideration of the coupling effects between the electrochemical and the thermal behaviors. The proposed model consists of two equivalent circuits. First, the electrochemical behaviors of the VRB are modeled by a second-order RC network taking account of the effects of concentration variation of the vanadium ions and the electrochemical activation. Second, a third-order Cauer network is used to model the heat transfer process in the VRB system, and the dynamic thermal behaviors of stacks, pipes and heat exchangers are characterized. Well-designed experiments and particle swarm optimization algorithm are use to identify the parametric values of the developed model. The proposed modeling method was validated experimentally using a 5kW/3kWh VRB platform, and the results show that the model is capable of accurately predicting the VRB performance under variable temperature conditions. The developed coupled electro-thermal model is then used for simulating and analyzing the performance of a VRB system operated in conjunction with a wind power plant under real-world conditions.

Highlights

The vanadium redox flow battery (VRB) has successfully demonstrated its competence in large-scale energy storage applications such as to provide peak shaving and power smoothing of renewable generation owning to its merits of safe operation, long cycling life, no cross contamination and flexible power/capacity design, etc. [1]–[6]
High temperature can cause severe problems such as electrolyte precipitation and flow channel blockage which can accelerate the aging of the battery
The model consists of a second-order RC electrical circuit model and a third-order Cauer network

Summary

INTRODUCTION

The vanadium redox flow battery (VRB) has successfully demonstrated its competence in large-scale energy storage applications such as to provide peak shaving and power smoothing of renewable generation owning to its merits of safe operation, long cycling life, no cross contamination and flexible power/capacity design, etc. [1]–[6]. Note that the thermal model does not need to be taken into consideration since the stack temperature Ts in this test is nearly constant This is due to a short charging time and a negligible amount of heat. To validate the developed model and the identified parameters, three constant current charge/discharge tests were carried out for round trip cycling at the ambient temperature of 20 ◦C. SIMULATION OF TEMPERATURE EFFECT In order to study the temperature effect on system performance, the electrolyte temperature variations of the stack, the pipes, and the heat exchanger are analyzed under several operating conditions In this case, a constant charging/discharging currents of 60 A was applied for VRB operation.

CASE STUDY

Findings

CONCLUSION