TIDUF64A December   2023  – August 2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
    2. 1.2 PV Input with Boost Converter
    3. 1.3 Bidirectional DC/DC Converter
    4. 1.4 DC/AC Converter
  8. 2System Design Theory
    1. 2.1 Boost Converter
      1. 2.1.1 Inductor Design
      2. 2.1.2 Rectifier Diode Selection
      3. 2.1.3 MPPT Operation
    2. 2.2 Bidirectional DC/DC Converter
      1. 2.2.1 Inductor Design
      2. 2.2.2 Low-Voltage Side Capacitor
      3. 2.2.3 High-Voltage Side Capacitor
    3. 2.3 DC/AC Converter
      1. 2.3.1 Boost Inductor Design
      2. 2.3.2 DC-Link Capacitor
  9. 3System Overview
    1. 3.1 Block Diagram
    2. 3.2 Design Considerations
      1. 3.2.1 Boost Converter
        1. 3.2.1.1 High-Frequency FETs
        2. 3.2.1.2 Input Voltage and Current Sense
      2. 3.2.2 Bidirectional DC/DC Converter
        1. 3.2.2.1 High-Frequency FETs
        2. 3.2.2.2 Current and Voltage Measurement
        3. 3.2.2.3 Input Relay
      3. 3.2.3 DC/AC Converter
        1. 3.2.3.1 High-Frequency FETs
        2. 3.2.3.2 Current Measurements
        3. 3.2.3.3 Voltage Measurements
        4. 3.2.3.4 Auxiliary Power Supply
        5. 3.2.3.5 Passive Components Selection
    3. 3.3 Highlighted Products
      1. 3.3.1  TMDSCNCD280039C - TMS320F280039C Evaluation Module C2000™ MCU controlCARD™
      2. 3.3.2  LMG3522R030 650-V 30-mΩ GaN FET With Integrated Driver, Protection and Temperature Reporting
      3. 3.3.3  TMCS1123 - Precision Hall-Effect Current Sensor
      4. 3.3.4  AMC1302 - Precision, ±50-mV Input, Reinforced Isolated Amplifier
      5. 3.3.5  ISO7741 Robust EMC, Quad-channel, 3 Forward, 1 Reverse, Reinforced Digital Isolator
      6. 3.3.6  ISO7762 Robust EMC, Six-Channel, 4 Forward, 2 Reverse, Reinforced Digital Isolator
      7. 3.3.7  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. 3.3.8  ISOW1044 Low-Emissions, 5-kVRMS Isolated CAN FD Transceiver With Integrated DC/DC Power
      9. 3.3.9  ISOW1412 Low-Emissions, 500kbps, Reinforced Isolated RS-485, RS-422 Transceiver With Integrated Power
      10. 3.3.10 OPA4388 Quad, 10-MHz, CMOS, Zero-Drift, Zero-Crossover, True RRIO Precision Operational Amplifier
      11. 3.3.11 OPA2388 Dual, 10-MHz, CMOS, Zero-Drift, Zero-Crossover, True RRIO Precision Operational Amplifier
      12. 3.3.12 INA181 26-V Bidirectional 350-kHz Current-Sense Amplifier
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
    2. 4.2 Note
    3. 4.3 Test Setup
      1. 4.3.1 Boost Stage
      2. 4.3.2 Bidirectional DC/DC Stage - Buck-Mode
      3. 4.3.3 DC/AC Stage
    4. 4.4 Test Results
      1. 4.4.1 Boost Converter
      2. 4.4.2 Bidirectional DC/DC Converter
        1. 4.4.2.1 Buck Mode
        2. 4.4.2.2 Boost Mode
      3. 4.4.3 DC/AC Converter
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Authors
  13. 7Revision History

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 irradiation 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, the GaN FETs allow the EMI filter and heat sink to be smaller, making the system more compact and lighter, thereby 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 boost converter
  • Battery input with bidirectional DC/DC converter
  • DC/AC converter

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

The first board, called DC/DC board, consists of two input boost 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 and additional thermal interface material to the SiC diode. The heat sink in the design is supposed to work in static cooling condition and the size is 324mm × 305mm × 57mm. Overall system dimension is 300mm × 280mm × 48mm, thus leading to a volume of 4 liters and a form factor of 2.5kW/l.