TIDUF88 October   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Accuracy of Bus Voltage Measuring
      2. 2.2.2 Shunt Current Measuring
      3. 2.2.3 Insulation Impedance Monitor
    3. 2.3 Highlighted Products
      1. 2.3.1 BQ79731-Q1
      2. 2.3.2 TPSI2140-Q1
      3. 2.3.3 ISO7841
      4. 2.3.4 SN6507
      5. 2.3.5 TPS7B6950
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Bus Voltage Accuracy
      2. 3.3.2 Current Sensing Accuracy
      3. 3.3.3 Insulation Impedance Accuracy
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

1 System Description

A Battery Energy Storage System (BESS) is a technology that stores electrical energy in the form of chemical energy within batteries. This stored energy can be later converted back into electricity and released when needed. BESS plays a crucial role in enhancing the reliability, stability, and efficiency of electrical power systems.

A BESS often consists of multiple battery racks arranged in a modular and scalable manner to meet the energy storage needs of a particular application. Each rack within a BESS typically includes a set of batteries, a battery management System (BMS), and associated hardware to facilitate energy storage, monitoring, and control. Battery racks are the physical structures that house the individual batteries. Battery racks provide a secure and organized framework for mounting the batteries, maintaining stability, and safety. The number of battery racks in a BESS depends on the required capacity and the specific design of the energy storage system.

The high-voltage monitor unit (HMU) part of a BMS is a critical component that focuses on managing and maintaining the safety of the high-voltage aspects of a battery pack. The following items are key elements typically found in the high-voltage part of a high-voltage BMS:

  1. Voltage measurement: BMS includes specialized circuits to measure the voltage of individual battery cells or modules within the high-voltage battery pack. Accurate voltage monitoring is crucial for maintaining the health and safety of the battery system.
  2. Current measurement: Current sensors are integrated into the high-voltage circuit to measure the charging and discharging currents of the battery pack. This information is essential for state-of-charge estimation and preventing overcurrent conditions.
  3. Insulation impedance monitoring devices: Instruments that monitor the isolation integrity of the high-voltage components to detect and prevent isolation failures.
  4. Communication interface: Interfaces such as Controller Area Network (CAN), or other communication protocols, allow the high-voltage BMS to exchange information with other parts of the vehicle or energy storage system.
  5. Isolation devices: Devices providing electrical isolation between the high-voltage battery and the rest of the BMS control electronics. This isolation is crucial for safety and preventing electrical interference.
  6. Emergency shutdown mechanisms: Emergency shutdown features can be implemented to rapidly disconnect the high-voltage battery pack in critical situations, maintaining the safety of the system and personnel.

These components collectively form the high-voltage part of a BMS, enabling precise monitoring, control, and protection of the high-voltage battery pack in applications like electric vehicles or large-scale energy storage systems.

This design focuses on high-voltage monitoring of large capacity battery rack applications, which can be applied in residential, commercial, industrial, grid BESS, and more. The design uses one BQ79731-Q1(battery junction box voltage monitor, current sensor, and isolation impedance sensor) device to measure four bus voltages and one shunt current. The design uses the TPSI2140-Q1 device and reed relay in a high-voltage, side-grounded, unbalanced bridge to calculate a precise insulation impedance of BESS up to 1500V. The design uses the SN6507 device and the transformer to convert 24V in the low-voltage side to 12V in the high-voltage side.

The design achieves the 1500V reinforced insulation requirement of UL1973 or IEC60664-1-2020. Wide-body isolation products including the digital isolator ISO7841DWWR, a transformer, and a ladder of resistors are used in consideration of the reinforced insulation requirement.