Autonomous Control for Cooperative Operation Between Energy Storage Systems

This paper proposes an autonomous control to power sharing between Energy Storage Systems (ESS). ESSs are installed in a distributed, these connect to the DC grid, and the ESSs share power autonomously without communication. The proposed autonomous control solves the power sharing problem caused by communication failures. Autonomous control is based on traditional voltage droop control, but virtual resistance is a fixed value and it is characterized by manipulating the reference voltage. This control law is installed in each ESS. Each ESS manipulates the reference voltage, and the power is distributed in a coordinated manner according to the number and status of the ESSs. For ESS operation control, a method of switching between charge and discharge modes based on the battery SOC (State Of Charge) threshold has been proposed in other papers. In this method, when all ESSs below the threshold, all ESSs enter the same mode, which means that power cannot be shared and there is a high risk of system down or lifetime decrease in some situations. To solve this problem, this paper proposes a control method for sharing operation that averages the SOC of each ESS without mode switching. This paper derives the basic control law and control method of this autonomous control, quantitatively consider the amount of power sharing, and confirm its validity by experiments.