TIDUF55 November   2023

 

  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 Power Tree and Wakeup
      2. 2.2.2 Insulation Requirement for Isolated Interface
      3. 2.2.3 Robust Relay Driver
      4. 2.2.4 Stackable Daisy Chain Communication
    3. 2.3 Highlighted Products
      1. 2.3.1  TMDSCNCD263
      2. 2.3.2  LMR51440
      3. 2.3.3  TPS7A16
      4. 2.3.4  TPS7B81
      5. 2.3.5  TPS62913
      6. 2.3.6  TPS4H160-Q1
      7. 2.3.7  ULN2803C
      8. 2.3.8  ISO1042
      9. 2.3.9  UCC12050
      10. 2.3.10 ISO1410
      11. 2.3.11 SN6505B
      12. 2.3.12 BQ32002
      13. 2.3.13 HDC3020
      14. 2.3.14 TPS3823
      15. 2.3.15 DP83826E
      16. 2.3.16 TPS763
      17. 2.3.17 LM74701-Q1
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Software Requirements
    3. 3.3 Test Setup
    4. 3.4 Test Results
      1. 3.4.1 Power Supply Testing
      2. 3.4.2 Daisy Chain Signal Quality
      3. 3.4.3 Relay Driving
      4. 3.4.4 Isolated CAN Transceiver Operation
  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

Currently, a battery energy storage system (BESS) plays an important role in residential, commercial and industrial, grid energy storage and management. BESS has various high-voltage system structures. Commercial, industrial, and grid BESS contain several racks that each contain packs in a stack. A residential BESS contains one rack.

A rack is a integrated module to compose the BESS. A rack consists of packs in a matter of parallel connection. Since battery cells require a proper working and storage temperature, voltage range, and current range for lifecycle and safety, it is important to monitor and protect the battery cell at the rack level.

A battery control unit (BCU) is a controller designed to be installed in the rack to manage racks or single pack energy. The BCU performs the following:

  • Communicates with the battery system management unit (BSMU), battery power conversion system (PCS), high-voltage monitor unit (HMU), and battery monitor unit (BMU)
  • Estimates Pack or Rack state of charge (SOC) and state of health (SOH)
  • Battery cluster balancing, thermal management, power (relay) ON and OFF
  • Limits charging and discharging current
  • Power supply to other systems

An HMU is a controller designed to be installed in the rack to keep monitoring racks and single pack status including rack voltage, current, single or accumulated charging and discharging, cycle time, and insulation. The BCU is used with the HMU to complete a full function of protection and energy management in at the rack level. The BMU is a controller designed to be installed in the pack to keep monitoring voltage and temperature of each battery cell for the total lifecycle.

The information collected by the HMU and BMU is transmitted to the BCU for safety and energy management. A robust and fast-speed communication is also required between the BMU and BCU or the HMU and BCU. A CAN is traditionally and widely used for robustness of communication. A CAN structure controller needs a MCU, a digital isolator, and an isolated power module to operate CAN communication functions. Efficient power consumption management of the isolated interface and MCU on the pack-side is crucial for CAN.

A daisy chain is offered as an optional plan to replace CAN. Compared with a CAN interface, only a couple of transformers are needed in BMU, HMU, and BCU. Thus, daisy chain provides an advantage in cost over CAN especially in high-capacity battery pack applications since cost is a concern for CAN structure in large-capacity BESS which consists of lots of BMU nodes and CAN interface devices. The insulation requirement also increases cost. Using reinforced insulation between BMU, HMU, and BCU communication interfaces increases the cost in the digital isolator and isolated power module.

The BCU needs to transmit the SOC, SOH, and rack status to the PCS and BSMU to operate the whole energy storage function. CAN, RS-485, and Ethernet is widely used in the communication interface.

The BCU switches relays ON or OFF to keep the rack works safely based on the SOC, SOH, and rack status like rack current, voltage, temperature and insulation status. SOC and SOH is estimated from the accurate information of pack and rack.

This design focuses on large capacity battery rack applications and applications that can be applied in residential, commercial, and industrial, grid BESS and more. The design uses a connector interface to the TMDSCNCD263 (AM263x general-purpose controlCARD development kit Arm® based MCU) to test all the functions. The external watchdog TPS3823 is employed to make sure the MCU operates reliably. The design contains one TPS4H160 and two ULN2803 devices to switch the power supply of the relay coils ON or OFF and make a full diagnostics and high-accuracy current sense of relay coils. The design contains three ISO1042 devices, one ISO1410, one DP83826E, and two BQ79600 devices for the communication interface. The UCC12050 and SN6505 devices are used for isolated power supply. The design also connects the real-time clock BQ32002 to log data and the humidity sensor HDC3020 to monitor the condensation status of rack or pack.