Optimal dispatch control of energy storage systems using forward-backward induction

The integration of distributed energy resources (DERs) into the power grid provides support for a significant share of the total power load and helps reduce transmission power losses. However, these advantages are not always guaranteed since the power profiles of DERs have high variability and the number of DERs is too many to control on an individual basis. In a hybrid energy system, these problems are counteracted through the aggregation and balancing of the variability of each distributed energy resource. This paper discusses optimal dispatch control mechanisms for 200 V, 500 Ah battery energy storage systems that support a 10 MW hybrid energy system, composed of distributed energy sources such as 1 MW solar photovoltaic (PV) generation and a 9 MW wind turbine based generation.

The proposed mechanisms focus on the dispatch control of energy storage systems using forward and backward induction. For that purpose, the interdependence of frequency, state of charge (SOC), undercharge and reversible effects in the battery energy systems were used to identify the optimal operating margin for the dispatch of the energy storage systems. The hybrid energy system was implemented using Matlab-Simulink and the dispatch control mechanism was programmed using IBM CPLEX studio. With such setup, the hybrid system was able to maintain 85 % capacity factor per day while the system interruption and unavailability were reduced by 65 %. The results demonstrate that the functionality of DERs increases significantly while being supported by optimally dispatched energy storage systems.

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