Battery Energy Storage System Components and Relationships
Between Each Component
In our previous article, we have defined what an energy storage is by using parameters like SoH, EoL, battery capacity, round-trip efficiency etc. to establish a base information set for procurement and simulation purposes. In this article, we will define the systemic components of battery energy storage system (BESS), which have different purposes on their own as well as the relationships between each component will be explained to understand why they are complementing each other.
A well-defined battery energy storage system consists of four different components. These are battery and battery management system (BMS), inverter or power conversion systems (PCS), energy management system (EMS) and auxiliary equipment. To ease the understanding of roles and
responsibilities of system, we have used pool analogy. You will find it easier to visualize each component.
1) Battery and Battery Management System
Independent from battery technology, this component mainly provides battery capacity. Chemical batteries (like lithium-ion) consist of battery packs, which is the first step of battery production. Identical packs are later assembled with each other, and a battery management system controls them to charge and discharge. If we use a pool analogy, battery packs will be small pools using the same pipes with outer world. Battery management system controls each small pool and audits them.
2) Power Conversion System (PCS) or Inverter
This component is the interim equipment of the battery with grid. It converts battery electricity (mostly DC) to grid electricity (AC). Different battery technologies use different power conversion systems, these power conversion systems can be generators for thermal and gravitational storage systems while it is a power electronics converter for li-ion batteries. Power conversion system should be compatible with the battery. For li-ion applications, maximum and minimum voltages of the battery should be in the operating range of the inverter because maximum power applied to inverter should not exceed maximum power of the battery while real-time maximum charge and discharge powers should be sent into the inverter. Therefore, there is a communication obligation between inverter and battery. This obligation can be obtained by direct communication, or it can be done by an Energy Management System (EMS). PCS is the main pump at the pool analogy, connected to the main pipe of the pool, it can pump water to/from the pool.
3) Energy Management System (EMS)
This component is the brain of the Battery Energy Storage System (BESS). It monitors the BESS and other relevant data sources (analyzers, switchgears etc.) in real-time and controls them according to pre-defined scenarios. Active operation modes or the parameters of them can be changed via EMS interface. These modes are the scenarios that we call “Use Cases” such as Peak Shaving, Microgrid Management, Energy Arbitrage etc. The user controls the BESS via controlling the energy management system. EMS communicates with BMS, PCS and auxiliary equipment inside BESS container. At the pool analogy, it is like a pool manager, deciding when to fill, drain, clean, or change the temperature of the pool.
4) Auxiliary Equipment
Auxiliary equipment is a group of components consisting of different sensors and devices (Temperature sensors, smoke sensors, fire suppression systems and air conditioning systems) that measure the
contingency cases and status of BESS. EMS has pre-defined scenarios when a fire occurs or temperature limits are reached inside the container. Response data for these scenarios comes from auxiliary equipment. Results or these scenarios may end up with shut down or disconnection of the BESS. At the pool analogy, this equipment is doing same thing, measuring water temperature, draining pool when an emergency occurs.
To apply use cases to the BESS like energy arbitrage, frequency control or peak shaving, understanding these components is essential. Investors should define these use cases at the feasibility stage and include these in EMS scenarios. Even though an energy market enabler like smartPulse is needed for making energy arbitrage, successful implementation of these use cases is related with the capabilities of each component. Most of the people think BMS is getting charge and discharge command from EMS
when battery charges/discharges but in fact PCS is getting this command from EMS and BMS is just responding the current being drawn by PCS. BMS provides feedback for maximum charging and discharging current to the PCS to have a safe operation.
In the next article, we will share the trading operation options for the energy storage via frequency control, day ahead and/or intraday market. This will include some numerical examples as well as what solutions we are providing to our clients as a market access enabler, and an optimization provider.
Rıfat Anıl Aydın
