Quantifying the impact of battery constraints on microgrid operation using optimal control

This paper presents an approach to quantify the impact of critical battery constraints on the optimal operating performance of a grid-tied microgrid. For a chosen set of solar power, load and grid cost conditions, a dynamic programming (DP) based optimal control algorithm minimizes imported grid energy costs. The microgrid operation is optimized for different constraint values using DP. For example, imported grid energy costs are minimized with and without an important practical constraint such as constant current constant voltage (CCCV) battery charging. The increase in grid energy costs due to this necessary constraint quantifies its impact on the microgrid´s performance. In this manner, we present an optimal vs. optimal comparison to capture the impact of constraints on grid costs or other objectives of interest. The unique contributions of this paper are our rigorous approach to evaluate the impact of constraints and the value of our results. It was observed that constraints on battery charging and battery capacity can result in significant increase in optimal cost of microgrid operation for the conditions assumed in our study.