TIDUF64 December   2023

 

  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
    2. 2.2 Design Considerations
      1. 2.2.1 DC-DC Boost Converter
      2. 2.2.2 Bidirectional DC-DC Converter
      3. 2.2.3 DC-AC Converter
    3. 2.3 Highlighted Products
      1. 2.3.1  TMDSCNCD280039C - TMS320F280039C Evaluation Module C2000™ MCU controlCARD™
      2. 2.3.2  LMG3522R030 650-V 30-mΩ GaN FET With Integrated Driver, Protection and Temperature Reporting
      3. 2.3.3  TMCS1123 - Precision Hall-Effect Current Sensor
      4. 2.3.4  AMC1302 - Precision, ±50-mV Input, Reinforced Isolated Amplifier
      5. 2.3.5  ISO7741 Robust EMC, Quad-channel, 3 Forward, 1 Reverse, Reinforced Digital Isolator
      6. 2.3.6  ISO7762 Robust EMC, Six-Channel, 4 Forward, 2 Reverse, Reinforced Digital Isolator
      7. 2.3.7  UCC14131-Q1 Automotive, 1.5-W, 12-V to 15-V VIN, 12-V to 15-V VOUT, High-Density > 5-kVRMS Isolated DC/DC Module
      8. 2.3.8  ISOW1044 Low-Emissions, 5-kVRMS Isolated CAN FD Transceiver With Integrated DC/DC Power
      9. 2.3.9  ISOW1412 Low-Emissions, 500kbps, Reinforced Isolated RS-485, RS-422 Transceiver With Integrated Power
      10. 2.3.10 OPA4388 Quad, 10-MHz, CMOS, Zero-Drift, Zero-Crossover, True RRIO Precision Operational Amplifier
      11. 2.3.11 OPA2388 Dual, 10-MHz, CMOS, Zero-Drift, Zero-Crossover, True RRIO Precision Operational Amplifier
      12. 2.3.12 INA181 26-V Bidirectional 350-kHz Current-Sense Amplifier
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
      1. 3.2.1 DC-DC Boost Stage
      2. 3.2.2 Bidirectional DC-DC Stage
    3. 3.3 Test Results
      1. 3.3.1 DC-DC Boost Converter
      2. 3.3.2 Bidirectional DC-DC Converter
  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

1 System Description

With an increase in demand for photovoltaic systems, inverters play an important role in facilitating the transition to renewable energy further and making solar energy more accessible for residential purposes. The modularity of string inverters, low cost-per-watt and easy amplification to attain higher power levels makes string inverters a good candidate for the single-phase market. With the additional possibility of energy storage via batteries, hybrid string inverters provide a good outlet to maximize the power utilization of the string input, and also provide an alternate pathway to supply the grid during night or low irradiance scenarios.

Such hybrid string inverters combine PV panel power point tracking with an inverter stage and bidirectional capabilities to include a battery stage, thus increasing the need for higher power density and efficiencies. This is where Gallium Nitrate (GaN) FETs can bring multiple benefits into the picture. Since GaN FETs support high switching frequencies, GaN FETs allow the EMI filter and heat sink to be smaller, making the system more compact and lighter, thus increasing the form factor of the design.

This reference design is intended to show an implementation of a two-channel single-phase string inverter with fully bidirectional power flow to combine PV input functionality with BESS supporting a wide range of battery voltages.

The design contains three main stages:

  • 2 × PV input with DC-DC boost converter
  • Battery input with bidirectional DC-DC converter
  • DC-AC converter

This system consists of two boards that are split by different functions.

The first board, called DC-DC board, consists of two input DC-DC converters for the individual string inputs and a DC-DC converter associated with the battery stage. The second board, called DC-AC board, consists of DC-link capacitors, DC-AC converter and filtering circuits. All the high-frequency switching components in the design are based on top-side cooled GaN FETs from TI .

Both the boards are mounted above an aluminum heat sink which is connected by means of thermal interface materials to the GaN FETs. The heat sink in the design is supposed to work in static cooling condition and the size is 324 mm × 305 mm × 57 mm. Overall system dimension is 290 mm × 275 mm × 47 mm, thus leading to a volume of 3.7 liters.