TIDUEZ0A March   2021  – March 2022 TMS320F28P550SJ , TMS320F28P559SJ-Q1

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Three-Phase ANPC Inverter Architecture Overview
      2. 2.2.2 LCL Filter Design
      3. 2.2.3 Power Switching Devices Selection
      4. 2.2.4 GaN Power Stage
      5. 2.2.5 Voltage Sensing
      6. 2.2.6 Current Sensing
      7. 2.2.7 System Power Supplies
        1. 2.2.7.1 Isolated Bias Supplies
      8. 2.2.8 Si Gate Driver Circuit
  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
    2. 3.2 Testing TIDA-010210 With AC Resistive Load
      1. 3.2.1 Test Setup
      2. 3.2.2 Experimental Results
    3. 3.3 Testing TIDA-010210 in PFC Operation
      1. 3.3.1 Test Setup
      2. 3.3.2 Experimental Results
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 Altium Project
      4. 4.1.4 Gerber Files
      5. 4.1.5 Assembly Drawings
    2. 4.2 Tools and Software
    3. 4.3 Support Resources
    4. 4.4 Trademarks
  10. 5About the Authors
  11. 6Revision History

1 System Description

Modern commercial scale solar inverters are seeing innovation on multiple fronts, which lead to smaller, higher efficiency products in the market:

  • The move to higher voltage solar arrays
  • Reducing the size of onboard magnetics
  • Inclusion of localized power storage requiring bidirectional power stages

By increasing the voltage to 1000-V or 1500-V DC from the array, the current can be reduced to maintain the same power levels. The reduction in current reduces conduction losses and hence results in higher efficiency. The reduction in di/dt also reduces the stress on electrical components. However, high DC bus voltages can limit the choice of power components that can be used as devices with higher voltage withstand capability is needed.

To compensate for the voltage stresses generated by high-voltage solar arrays, new topologies of solar inverters have been designed. Traditional half bridges block the full input voltage on each switching device. By adding additional power components, the overall stress on the device can be significantly reduced. This reference design shows how to implement a three-level ANPC converter that limits the voltage stress on all the power components to only half the DC bus voltage, allowing use of more abundant and faster power components. This design also demonstrates the use GaN devices in solar inverters which was not possible with other topologies due to their limitation of voltage withstand capability.

Additional power density is also being enabled by moving to higher switching speeds in power converters. As this design shows, a higher switching speed reduces the overall size requirement of the output filter stage—a primary contributor to the design size.

Though multilevel topologies enable the use of lower voltage switching devices, they come with certain limitations – the need to drive more switches and need to avoid overvoltage even during abnormal operation. This design tries to demonstrate how to address all 18 power devices in the power stage with the limited number of PWMs available from a common MCU and also how to implement hardware based interlocking protections needed to avoid device overvoltage under all operating conditions without the use of additional components.

Another requirement that is becoming more prevalent for inverter power stages is the need for bidirectional power transfer. This is important in storage ready inverters where there can be a need for the power from the grid to be stored in local power storage like a battery. The power conversion stage in an electronic energy storage system also has the same requirement. The ANPC power stage demonstrated in this design is inherently capable of bidirectional operation – only software is required for it to operate either as inverter or power factor controller (PFC). Currently the design is tested in inverter mode operation and the testing in PFC mode is in progress.