Real-time control of battery energy storage system to provide grid services considering dynamic DC-AC converter capability curves

We design and experimentally validate a real-time control system for battery energy storage systems (BESSs) to provide frequency control and voltage support to power grids. The objective of the control system is to utilize the full power capability of the BESSs to provide ancillary services. We take into account the dynamic capability curve of the DC-AC converter and the security requirements of the BESSs as constrains of the control system. The initial power set-points are obtained based on the traditional droop control approach. The final power set-points calculation is formulated as a nonconvex optimization problem. A convex reformulation of the original control problem is proposed. We prove that the proposed convex optimization gives the global optimal solution to the initial nonconvex problem. Finally, we improve the performance of this algorithm by reformulating and discretizing the feasible region of the optimization model. We achieve a 100 ms update time of the controller setpoint and experimentally validate the real-time control system in the utility-scale 720 kVA / 560 kWh BESS on EPFL campus.