TIDUF85A August   2024  – December 2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
      1. 2.1.1 Subsystems
        1. 2.1.1.1 Arc Detection Channels
          1. 2.1.1.1.1 Isolated Current Measurement
          2. 2.1.1.1.2 Band-Pass Filter
          3. 2.1.1.1.3 Analog-to-Digital Conversion
          4. 2.1.1.1.4 Arc Detection Using Embedded AI Models
        2. 2.1.1.2 Arc Labeling Circuit
          1. 2.1.1.2.1 Isolated String Voltage Measurement
          2. 2.1.1.2.2 Isolated Arc Voltage Measurement With Isolated Comparator
          3. 2.1.1.2.3 Window Comparator for Advanced Labeling
    2. 2.2 Design Considerations
      1. 2.2.1 Current Sensor and Input Stage
      2. 2.2.2 Analog Band-Pass Filter
      3. 2.2.3 Arc-Labeling Circuit
        1. 2.2.3.1 String Voltage Sensing
        2. 2.2.3.2 Arc Gap Voltage Sensing
        3. 2.2.3.3 Differential to Single-Ended Conversion
        4. 2.2.3.4 Window Comparator for Arc Labeling
      4. 2.2.4 Auxiliary Power Supply
      5. 2.2.5 controlCard and Debug Interface
    3. 2.3 Highlighted Products
      1. 2.3.1 TIEVM-ARC-AFE
      2. 2.3.2 TMDSCNCD28P55X – TMDSCNCD28P55X controlCARD Evaluation Module
        1. 2.3.2.1 Hardware Features
      3. 2.3.3 OPA4323 – Quad, 5.5V, 20MHz, Zero-Cross Low-Noise (6nV/√Hz) RRIO Operational Amplifier
      4. 2.3.4 OPA323 – Single, 5.5V, 20MHz, Zero-Cross Low-Noise (6nV/√Hz) RRIO Operational Amplifier
      5. 2.3.5 AMC3330 – ±1V Input, Precision Voltage Sensing Reinforced Isolated Amplifier With Integrated DC/DC
      6. 2.3.6 AMC23C11 – Fast-Response, Reinforced, Isolated Comparator With Adjustable Threshold and Latch Function
  9. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Signal Chain Verification
      1. 3.1.1 Hardware Requirements
      2. 3.1.2 Test Setup
      3. 3.1.3 Test Results
    2. 3.2 Arc Testing
  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
  12. 6Revision History

3.1.3 Test Results

Figure 3-2 shows the transfer function of the current transformer circuit with different DC currents applied. This is done by feeding two cables through the current transformer. One is carrying a AC signal with varying frequency for the AC analysis, while the second cable is carrying a DC current. The input current is measured with a high-performance current probe of an oscilloscope. The output voltage is measured on TP9 which is labeled CT+.

High DC currents lead to saturation effects especially for low frequencies. In the band from 30kHz to 100kHz which is used for arc detection the attenuation is around 3dB for a current of 20A which is acceptable. If higher DC currents are present in the system, an external sensor which can handle these currents can be used. The signal chain needs to be adjusted accordingly.

TIDA-010955 Transfer Curve of the Current Transformer for Different DC CurrentsFigure 3-2 Transfer Curve of the Current Transformer for Different DC Currents

Figure 3-3 shows the transfer curve between the output of the CT circuit and the output of the gain stage. A stable gain of 20dB (Gain of 10) is achieved up 100kHz which is the upper limit of the frequency range used for arc detection.

TIDA-010955 Transfer Curve of Gain StageFigure 3-3 Transfer Curve of Gain Stage

Figure 3-4 and Figure 3-5 show the transfer curves of the filter stage. Channel 1 and channel 2 are implemented as a 8th order band-pass filter while channel 3 and channel 4 are implemented as a 4th order band-pass filter. These transfer curves are measured between TP2 (output of the gain stage) and TP1 (output of the band-pass filter stage).

TIDA-010955 Transfer Curve of 8th Order Band-Pass Filter Stage (CH1 and CH2)Figure 3-4 Transfer Curve of 8th Order Band-Pass Filter Stage (CH1 and CH2)
TIDA-010955 Transfer Curve of 4th Order Band-Pass Filter Stage (CH3 and CH4)Figure 3-5 Transfer Curve of 4th Order Band-Pass Filter Stage (CH3 and CH4)

Figure 3-2 and Figure 3-3 show the transfer curves of the complete signal chain for channel 1 with a 8th order band-pass filter and channel 3 with a 4th order band-pass filter.

TIDA-010955 Transfer Curve of Analog Signal Chain With 8th Order Band-Pass Filter (CH1 and CH2)Figure 3-6 Transfer Curve of Analog Signal Chain With 8th Order Band-Pass Filter (CH1 and CH2)
TIDA-010955 Transfer Curve of Analog Signal Chain With 4th Order Band-Pass Filter (CH3 and CH4)Figure 3-7 Transfer Curve of Analog Signal Chain With 4th Order Band-Pass Filter (CH3 and CH4)