TIDUEZ9B July   2022  – April 2023

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Isolated Current Measurement
    2. 1.2 Band-Pass Filter
    3. 1.3 Analog-to-Digital Conversion
    4. 1.4 Arc Detection Algorithm
    5. 1.5 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Current Transformer Circuit
      2. 2.2.2 Analog Band-Pass Filter
      3. 2.2.3 Analog-to-Digital Conversion
      4. 2.2.4 Power Supply
      5. 2.2.5 Debugging and Status Indication Options
    3. 2.3 Highlighted Products
      1. 2.3.1 TPS259474
      2. 2.3.2 TPS562202
      3. 2.3.3 TPS745
      4. 2.3.4 OPAx322
      5. 2.3.5 ADS8363
      6. 2.3.6 REF5025
      7. 2.3.7 TMDSCNCD280049C
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware and Software Requirements
      1. 3.1.1 Hardware
      2. 3.1.2 Software
        1. 3.1.2.1 Arc Detection Theory
        2. 3.1.2.2 Software Implementation
    2. 3.2 Test Setup
      1. 3.2.1 ControlCARD Configuration
      2. 3.2.2 Setup for Hardware and Software Validation
      3. 3.2.3 Setup for Arc Testing
    3. 3.3 Test Results
      1. 3.3.1 Test Results of Hardware and Software Validation
      2. 3.3.2 Testing With Arcs
  9. 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 Support Resources
    4. 4.4 Trademarks
  10. 5About the Author
  11. 6Revision History

2.2.1 Current Transformer Circuit

For sensing the AC noise on the DC current between solar string and inverter a current transformer (CT) based approach is selected. This has the advantage that the large DC component which is not of interest for the arc detection is filtered out right away. Since a large DC current is fed through the CT, the saturation behavior is very important. For higher DC currents gapped ferrite cores or powdered metal cores with lower permeability might be required. The circuit shown in Figure 2-2, consists of the CT, some passive components, and an amplifier. The burden resistor R5 is selected with 200 Ω according to the data sheet, which leads to a current to voltage ration of 1:1 for the AC components within the frequency band of the CT, which is 10 kHz to 200 kHz. The passives afterward are used for protection of the amplifier and to introduce a bias voltage of 2.5 V. The amplifier circuit introduces a gain of 10, to fit the output signal to the input voltage range of the following filter section. This gain can be reduced in case of bigger AC components present.

GUID-20220711-SS0I-KNFC-XVK6-QFF84VKMZFC1-low.svg Figure 2-2 Schematic Current Transformer Circuit and Gain Stage