Interpretation of Energy Storage System EMS, BMS, PCS

EMS, or Energy Management System, is a system for managing energy. The main functions of an EMS for energy storage include data collection and analysis from energy storage system equipment (such as PCS, BMS, meters, fire protection, air conditioning, etc.), as well as energy dispatching (mainly reflected in the operation of economic operation strategies and safety protection strategies).

An EMS is primarily used for internal energy control within microgrids to maintain power balance and ensure normal operation of the microgrid. The demand and application scenarios are diverse, and the workload of the software system is immense. It can meet the on-site energy dispatching needs of small and medium-sized commercial energy storage systems, while large energy storage systems will involve grid-side dispatching.

BMS, or Battery Management System, is a device that monitors the status of energy storage batteries. Its main functions include intelligent management and maintenance of individual battery cells to prevent overcharging and overdischarging, thereby extending the battery's lifespan and monitoring its condition. The form of a BMS typically consists of one (or multiple) circuit board(s) or hardware box(es).

Architecturally, BMS can be divided into two types: centralized and distributed. The former uses a single BMS box to manage all cells, suitable for situations with fewer cells, while the latter is used in energy storage stations due to the large number of cells, often featuring a three-tier architecture of master control, main control, and slave control.

From a hierarchical perspective, BMS operates on the underlying battery side, while EMS affects the entire microgrid system. In general small-scale energy storage systems, only BMS might be used for battery management without employing EMS for overall dispatching.

BMS is a part of EMS and there exists an internal and external interactive relationship.

Communication between Energy Storage BMS and EMS:

Uploading Information: The information uploaded by BMS includes individual cell (or group) data such as cell voltage, battery pack voltage, charge/discharge current, maximum SOC of individual cells, minimum SOC of individual cells, minimum SOH of individual cells; battery pack SOC, maximum temperature of individual cells, minimum temperature of individual cells, ambient temperature, as well as related information on battery abnormalities, alarms, protection, etc.

Receiving Information: BMS receives operational parameters for the batteries issued by the monitoring system EMS, such as protective settings for voltage, alarm settings for voltage, protective settings for temperature, alarm settings for temperature, protective settings for SOC, and alarm settings for SOC, etc.

PCS stands for Power Conversion System, which is a storage converter. It is the core component between the energy storage system and the power grid that enables bidirectional flow of electrical energy, used to control the charging and discharging process of batteries, and to perform AC/DC conversion.

It mainly consists of a DC/AC bidirectional converter, control unit, etc. By receiving EMS control commands and controlling the converter according to the commands to charge or discharge the battery. At the same time, PCS can communicate with BMS through CAN, RS485 interfaces, dry contact transmission, etc., to obtain battery pack status information, and can achieve protective charging and discharging of the battery, ensuring safe operation of the battery.

The Relationship Among the Three

(1) Energy Management System (EMS): Serves as the decision-making role, primarily responsible for data acquisition, network monitoring, and energy dispatching.

(2) Battery Management System (BMS): Serves as the sensory role, mainly in charge of battery monitoring, assessment, protection, and balancing.

(3) Power Conversion System (PCS): Serves as the executioner role, with the main function of controlling the charging and discharging processes of the energy storage battery pack and carrying out AC/DC conversion.