The Different Function Between BMS and EMS

Battery Management System

In the energy storage system, the battery pack feeds back the status information to the battery management system BMS, and the BMS shares it with the energy management system EMS and the energy storage converter PCS; the EMS sends the control information to the PCS and BMS based on optimization and scheduling decisions. , control the single cell/battery pack to complete charging and discharging, etc.

Battery management system BMS: plays a sensing role and is mainly responsible for battery monitoring, evaluation, protection and balancing;

Energy management system EMS: plays a decision-making role and is mainly responsible for data collection, network monitoring and energy scheduling;

Energy storage converter PCS: plays an executive role, and its main function is to control the charging and discharging process of the energy storage battery pack and perform AC to DC conversion. BMS (Battery Management System), the BMS battery system is commonly known as the battery nanny or battery manager. It is a device that monitors the status of energy storage batteries. BMS and battery cells together form a battery system.


BMS plays a sensing role in the energy storage system. Its main function is to monitor the operating status of each battery in the battery energy storage unit and ensure the safe operation of the energy storage unit. BMS measures the basic parameters of the battery, including voltage, current, temperature, etc., to prevent overcharging and over-discharging of the battery and extend the service life of the battery. BMS needs to calculate and analyze the battery’s SOC (battery remaining capacity) and SOH (battery health status), and report abnormal information timely.

Three-Level Architecture

Most BMS systems have a three-layer architecture, and the hardware is mainly divided into slave control units, master control units and master control units.

  1. Bottom layer: Slave control BMU, which is the single battery management layer. It consists of a battery monitoring chip and its auxiliary circuits. It is responsible for collecting various information of a single battery, calculating and analyzing the SOC (battery remaining capacity) and SOH (battery health status) of the battery, achieving active balancing of the single battery, and balancing the single battery. Body abnormality information is uploaded to the main control.
  2. Middle layer: Main control BCU, which is the battery pack management layer. Collect various single battery information uploaded by BMU and collect battery pack information. Calculate and analyze the SOC and SOH of the battery pack.
  3. Upper layer: master control, which is the battery cluster management layer. Responsible for the overall coordination within the system and external information interaction with EMS and PCS, and controlling the operation process of the entire BMS system according to external requests.

Technical Requirement

BMS is more complex and requires higher requirements than the BMS of automobile power batteries. Management battery capacity levels vary widely. The power supply managed by the energy storage BMS has reached the MWh level, and the number of series and parallel batteries is huge. Energy storage BMS has stricter grid connection requirements.

Energy storage EMS needs to be connected to the power grid and has higher requirements on harmonics, frequency, etc. One end of the power battery BMS is connected to the battery, and the other end is connected to the vehicle’s control and electronic system. The technical requirements are relatively lower.

Energy Management System

Development from basic functions to advanced functions

  1. BMS is an important guarantee for the safety, long life and low cost of energy storage systems. The non-uniformity of single cells can easily lead to the barrel effect, resulting in a reduction in actual charge and discharge depth and cycle life, resulting in direct economic losses; at the same time, it can easily lead to a decline in the safety performance of the battery system, directly affecting operational safety.
  2. EMS (Energy Management System) is the decision-making center of the energy storage system and acts as the “brain”. Energy management systems include grid-level energy management systems and microgrid-level energy management systems. The EMS mentioned in energy storage systems generally refers to the microgrid level.


EMS products generally serve as a hub for interaction between energy storage systems and higher-level information systems. The energy storage system participates in power grid dispatching, virtual power plant dispatching, “source grid load storage” interaction, etc. through EMS. EMS products work closely with power grid dispatching and have certain similarities in functions. Companies need to understand the operating characteristics of the power grid. Enterprises that are deeply involved in grid-side information have accumulated knowledge know-how, can form capability reuse, and have certain capabilities.





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