SLUAB06 January   2025 AMC131M02 , AMC3330 , ISO7731

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Topologies for Insulation Monitoring in ESS
    1. 2.1 Single Switch Topology
      1. 2.1.1 Test Steps
    2. 2.2 Dual Switch Floating Sampling Topology
      1. 2.2.1 Test Steps
    3. 2.3 Dual Switch Sampling in High Voltage Side Topology
    4. 2.4 AC Injection Topology
  6. 3Comparison of Designs
    1. 3.1 Injection Resistance Influence on Accuracy
  7. 4Capacitor Influence on Sampling Time
    1. 4.1 How to Choose Y Capacitor
    2. 4.2 Sampling Time
  8. 5Key Devices
    1. 5.1 BQ79731-Q1
    2. 5.2 UCC33421-Q1
    3. 5.3 AMC131M02
    4. 5.4 AMC3330
    5. 5.5 ISO773x
  9. 6Topos Simulation Result and Conclusion
  10. 7Summary
  11. 8References

3 Comparison of Designs

Control Block DiagramFigure 3-1 Control Block Diagram

The control block diagram for the topology of the dual switch, according to the requirements of the BMS for insulation detection and high voltage detection in the stored energy, is shown in the diagram above and requires both ends of the voltage drop before the sampling relay and after the relay is closed, if a differential ADC is used. Two voltage samples are required, and three voltage sampling channels are required if a single-ended ADC is used and the high-voltage negative side is considered a sampling site. Insulation monitoring and current monitoring of the shunt are also required.

This is why the system requires the use of transport, isolation, and ADCs for insulation voltage sampling, where isolation also requires additional power supply, and three ADCs for high-voltage sampling. Additional isolation and power supply are also required, as well as a single current sample.

Design1 Based on Topo 2Figure 3-2 Design1 Based on Topo 2

Depending on the sample point arrangement, there are three options to choose from, first is the integrated AMC3330 to take on the isolation and handling functions. Sampling using the MCU's ADC, high-voltage sampling and current sampling is done by BQ79731. If the two SSRs are controlled with the ADC on the high side, the control of the SSR and the high side do not need to withstand a medium strength test voltage of 4380V from a medium strength test point of view, so no additional isolation device is required to control the SSR.

Design2 Based on Topo 3Figure 3-3 Design2 Based on Topo 3

Second design is to use the AMC131M03 with two isolated ADCs and one current sampling, which is less expensive but less accurate for voltage and current sampling than BQ79731, while insulation sampling requires a dual channel AMC131M02. And the control signal of the SSR needs to be isolated to meet the requirements of the media strength test.

Design3 Based on Topo 1Figure 3-4 Design3 Based on Topo 1

The third design is a cost down design based on the topology of a single switch and a single sampling point, which uses BQ79731 to sample three voltages and the shunt current, and it can use GPIO in BQ79731 to control the switch without isolation, but it can be 5.3% lower in accuracy than the topology of the dual switch, but still meets the 20% requirements stipulated by the regulations.