There is a lot of discussion around the control and monitoring of a Battery Energy Storage System (BESS) and what an Energy Management System (EMS) for BESS actually does. Trying to shed some light on this question we present below the BESS ecosystem as shown from the control viewpoint.
The Bess Ecosystem. Source: Inaccess.
Each of the devices shown above have a different role in the overall system operation and more specifically (starting from the bottom):
As more and more owners and operators embrace energy storage, however, there is a growing realization that battery as The Slave Battery Management System (BMS) monitors basic quantities of a battery rack such as temperature, voltage and SOC. In many cases it is able to connect/ disconnect the rack on demand or in case of a fault.
The Master BMS aggregates the values from several slave BMSs and coordinates the connection/disconnection of racks. It also provides several automation functions that are protection related (e.g. in case of fire or high battery temperature). Finally, it offers the logging interface for the retrieval of measurements and alarms.
The Power Conversion system (PCS) is the AC/DC converter and the controllable asset of the system. It charges and discharges the batteries by accepting active/reactive power setpoints. In some cases, the PCS integrates with the BMS so that it can make decisions based on the SOC of the batteries, while in other cases this is done by the S-PPC.
The Storage Power Plant Controller (S-PPC) co-ordinates the operation of several PCSs and BMSs to offer active/reactive power control at site level, SOC management, SOC limits avoidance and SOC balancing for maximum availability. It also enables the provision of Frequency Response and Reserve services or advanced Hybrid site scenarios such as energy time shifting, ramp rate control and capacity firming.
The Dispatcher schedules and implements the control services either in a standalone or stacked manner.
The EMS Server monitors the battery site equipment and enables HMI-triggered control functionality and configuration. Furthermore, it provides several performance indicators and operation and maintenance related actions and tests.
The BESS Server records all the datapoints necessary for the warranty and claims management.
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