JAJU857 December   2022

 

  1.   概要
  2.   リソース
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 System Design Theory
      1. 2.2.1 Detection Principals
      2. 2.2.2 Saturation
      3. 2.2.3 General Mode of Operation
    3. 2.3 Highlighted Products
      1. 2.3.1 DRV8220
      2. 2.3.2 OPAx202
      3. 2.3.3 TLVx172
      4. 2.3.4 TLV7011
      5. 2.3.5 INA293
      6. 2.3.6 SN74LVC1G74
      7. 2.3.7 TLV767
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware
      1. 3.1.1  Board Overview
      2. 3.1.2  Filter Stage
      3. 3.1.3  Differential to Single-Ended Converter
      4. 3.1.4  Low-Pass Filter
      5. 3.1.5  Full-Wave Rectifier
      6. 3.1.6  DC Offset Circuit
      7. 3.1.7  Auto-Oscillation Circuit
        1.       31
      8. 3.1.8  DRV8220 H-Bridge
      9. 3.1.9  Saturation Detection Circuit
      10. 3.1.10 H-Bridge Controlled by DFF
      11. 3.1.11 MCU Selection
      12. 3.1.12 Move Away From Timer Capture
      13. 3.1.13 Differentiating DC and AC From the Same Signal
      14. 3.1.14 Fluxgate Sensor
    2. 3.2 Software Requirements
      1. 3.2.1 Software Description for Fault Detection
    3. 3.3 Test Setup
      1. 3.3.1 Ground-Fault Simulation
    4. 3.4 Test Results
      1. 3.4.1 Linearity Over Temperature
    5. 3.5 Fault Response Results
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 サポート・リソース
    4. 4.4 Trademarks
  10. 5About the Author

3.2.1 Software Description for Fault Detection

The MSP430F5132 internal ADC polls a filtered signal.

When a voltage greater than DC trip threshold is detected, the MSP430 enters a monitor mode. The highest and lowest readings determine whether a DC fault or AC fault has occurred. While in monitor mode, the highest and lowest values are saved over a detection window greater than 10 ms. The detection window needs to be more than 10 ms to make sure 0 V is detected if an AC fault occurs.

The code sequence is as follows:

  1. MCU samples ADC
  2. DC trip threshold is passed(2)
  3. Wait the duration of the detection window in milliseconds. A time of 13 ms was found to be most consistent to detect a zero during an AC fault. The window must be larger than 10 ms to detect a zero of a 50-Hz AC fault(3)
  4. Save the highest and lowest recorded values
  5. If the lowest value is greater than the DC trip threshold, a DC fault occurred.
  6. If the lowest value is near zero and the highest value is greater than the AC trip threshold, an AC fault occurred
  7. Trip type, AC or DC, is saved. GPIO output high.
  8. When the fault condition clears below hysteresis, GPIO returns low. Relay is reset via GPIO low.

If the lowest ADC reading is greater than the DC trip threshold, a DC fault occurred and the system trips the relay.

If the lowest ADC reading is zero, and the highest reading is greater than the AC trip threshold, an AC fault occurred and the system trips the relay.

This is how the software differentiates between the two fault types. The software must differentiate AC versus DC because the trip thresholds are different for each.

2. Use whichever threshold is lower: AC or DC. In this design, DC trip threshold is lower.
3. Ten ms is half the period of 50 Hz. Because the AC fault is full-wave rectified, half the period makes sure a zero is detected and successfully detects an AC fault.