Model for charging/discharging dynamics of cells in redox flow battery with transport delay

Abstract

A redox flow battery (RFB) is an energy storage capable of contributing to grid balancing under the fluctuation of renewable power sources and loads. An RFB consists of reaction cells and tanks containing electrolytes that are pumped to the cells. Modeling of the charging/discharging dynamics is necessary for controlling the flows of the electrolytes and the current. The previous researches have assumed that the transport delay is small and negligible. However, when the transport delay appears, it affects the performance of the control systems. This paper aims to propose a model for considering charging/discharging dynamics with transport delay. The delay appears in the voltages of the cells in the tested system, and a model is introduced to simulate the delay. The model is represented by delay differential equations (DDEs) of the ion concentration in the cells with the Nernst relationship. The DDEs are derived from the mass balance equation including the transport delay translated to the time delay. The simulation result excellently agrees well with the experiment at results. In other words, the model can predict the dynamics governed by the transport delay accurately.