TIDUDJ6B August   2022  – February 2023 OPA388-Q1

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagrams
    2. 2.2 Highlighted Products
      1. 2.2.1 TPSI2140-Q1
      2. 2.2.2 AMC1301-Q1
      3. 2.2.3 SN6501-Q1
    3. 2.3 System Design Theory
      1. 2.3.1 Isolation Leakage Current Theory
      2. 2.3.2 High-Voltage Measurement
  8. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Required Hardware
    2.     Hardware with Solid-State Relay
    3. 3.2 Testing and Results
      1. 3.2.1 Test Setup
      2. 3.2.2 Isolation Tests
        1. 3.2.2.1 Normal Conditions
        2. 3.2.2.2 Isolation Error at HV Positive
        3. 3.2.2.3 Isolation Error at HV Negative
        4. 3.2.2.4 Isolation Error at ¼ HV Battery Voltage
        5. 3.2.2.5 Isolation Error at ¾ HV Battery Voltage
        6. 3.2.2.6 Isolation Error at the Middle of an HV Battery Voltage
      3. 3.2.3 Solid-State Relay Isolation Tests
        1. 3.2.3.1 Normal Conditions
        2. 3.2.3.2 Isolation Error at HV Positive
        3. 3.2.3.3 Isolation Error at HV Negative
        4. 3.2.3.4 Isolation Error at ¼ HV Battery Voltage
        5. 3.2.3.5 Isolation Error at ¾ HV Battery Voltage
        6. 3.2.3.6 Isolation Error at the Middle of an HV Battery Voltage
      4. 3.2.4 High Voltage Measurements
      5. 3.2.5 Isolation Measurement Analysis
      6. 3.2.6 Error Analysis
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  10. 5Software Files
  11. 6Related Documentation
  12. 7Trademarks
  13. 8Revision History

1 System Description

In response to the latest changes in global environmental conditions and to reduce greenhouse gases, there is a need to have hybrid or electric traction units, which have very low or zero emissions. In a hybrid electric vehicle (HEV) or electric vehicle (EV), high-voltage batteries are used as storage elements to power the wheels. High-voltage batteries for automotive systems are defined as those with ≥ 60 V. Onboard chargers or external DC converters are used to source the power. Meanwhile, high-voltage batteries are used to store that energy. DC/DC converters and motor control inverters are used to power the wheels and other subsystems such as heating, ventilating, and air conditioning (HVAC). All these subsystems are working on high voltage.

GUID-71A69558-1100-45C1-A9D8-B2FF4A987B2D-low.gif Figure 1-1 Typical HEV / EV Power Train

High-voltage components in HEV or EV systems are typically isolated from the chassis for functional and occupant safety reasons. The level of isolation in systems completely depends on the application, subsystem location within the vehicle, and the effective peak operating voltage. In general, HEVs and EVs use functional, basic, and reinforced isolation-based devices (see #T5081059-4). Functional isolation is used for protecting ground loops and the operation of those devices. Basic isolation is a single level of isolation which provides basic protection against electric shock. Reinforced isolation is a double level of isolation which provides higher protection against electric shock. Automotive power-train system developers should select basic or reinforced isolated components based on the voltage of the battery and peak voltages of the onboard charger and inverter.

GUID-5D6C7A43-BDBE-4C28-9564-91313619444E-low.gif Figure 1-2 Isolation in HEV/EV

Isolation is a critical parameter for the safety of HEV and EV systems. Due to many factors such as improper motor winding, deteriorating wiring harnesses, general aging, and power dissipation, the operating temperature and peak electrical stress on semiconductors may lead to degradation or loss of isolation in these HEV and EV systems. Any single point for failure of isolation loss does not have much impact on the operation of the system, but it does become a potential life risk when operators make contact with this high-voltage operating environment. Vehicle manufacturers need to have a mechanism to detect every single point failure of isolation in a complete system and have a necessary preventive action in place. Measure isolation resistance and insulation leakage currents to check the safety of occupants in the HEV or EV system. As per FMVSS 305 specification, at least 500 Ω/V of isolation resistance must be maintained from high-voltage systems to chassis ground. Depending on the leakage current measured, HEV/EV system error-handling functions may be designed to take appropriate actions.. Functions or systems will be built to disconnect high-voltage relays and discharge the DC-link capacitors.

Checking the leakage or low ohmic resistance paths from high-voltage nets to the low-voltage chassis ground is important. The necessary isolation resistance is calculated based on battery voltage, creating a isolation breakage path and monitoring the deflections as explained in this design guide. Based on the vehicle architecture, the number of sampling points for isolation leakage measurements varies.