TIDUE53J March   2018  – February 2025 TMS320F28P550SG , TMS320F28P550SJ , TMS320F28P559SG-Q1 , TMS320F28P559SJ-Q1

 

  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 Highlighted Products
      1. 2.2.1  UCC21710
      2. 2.2.2  UCC5350
      3. 2.2.3  TMS320F28379D
      4. 2.2.4  AMC3306M05
      5. 2.2.5  OPA4388
      6. 2.2.6  TMCS1123
      7. 2.2.7  AMC0330R
      8. 2.2.8  AMC0381D
      9. 2.2.9  UCC14341
      10. 2.2.10 UCC33421
    3. 2.3 System Design Theory
      1. 2.3.1 Three-Phase T-Type Inverter
        1. 2.3.1.1 Architecture Overview
        2. 2.3.1.2 LCL Filter Design
        3. 2.3.1.3 Inductor Design
        4. 2.3.1.4 SiC MOSFETs Selection
        5. 2.3.1.5 Loss Estimations
      2. 2.3.2 Voltage Sensing
      3. 2.3.3 Current Sensing
      4. 2.3.4 System Auxiliary Power Supply
      5. 2.3.5 Gate Drivers
        1. 2.3.5.1 1200-V SiC MOSFETs
        2. 2.3.5.2 650-V SiC MOSFETs
        3. 2.3.5.3 Gate Driver Bias Supply
      6. 2.3.6 Control Design
        1. 2.3.6.1 Current Loop Design
        2. 2.3.6.2 PFC DC Bus Voltage Regulation Loop Design
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
        1. 3.1.1.1 Test Hardware Required
        2. 3.1.1.2 Microcontroller Resources Used on the Design (TMS320F28379D)
        3. 3.1.1.3 F28377D, F28379D Control-Card Settings
        4. 3.1.1.4 Microcontroller Resources Used on the Design (TMS320F280039C)
      2. 3.1.2 Software
        1. 3.1.2.1 Getting Started With Firmware
          1. 3.1.2.1.1 Opening the CCS project
          2. 3.1.2.1.2 Digital Power SDK Software Architecture
          3. 3.1.2.1.3 Interrupts and Lab Structure
          4. 3.1.2.1.4 Building, Loading, and Debugging the Firmware
          5. 3.1.2.1.5 CPU Loading
        2. 3.1.2.2 Protection Scheme
        3. 3.1.2.3 PWM Switching Scheme
        4. 3.1.2.4 ADC Loading
    2. 3.2 Testing and Results
      1. 3.2.1 Lab 1
      2. 3.2.2 Testing Inverter Operation
        1. 3.2.2.1 Lab 2
        2. 3.2.2.2 Lab 3
        3. 3.2.2.3 Lab 4
      3. 3.2.3 Testing PFC Operation
        1. 3.2.3.1 Lab 5
        2. 3.2.3.2 Lab 6
        3. 3.2.3.3 Lab 7
      4. 3.2.4 Test Setup for Efficiency
      5. 3.2.5 Test Results
        1. 3.2.5.1 PFC Mode
          1. 3.2.5.1.1 PFC Start-Up – 230 VRMS, 400 VL-L AC Voltage
          2. 3.2.5.1.2 Steady State Results - PFC Mode
          3. 3.2.5.1.3 Efficiency, THD, and Power Factor Results, 60 Hz – PFC Mode
          4. 3.2.5.1.4 Transient Test With Step Load Change
        2. 3.2.5.2 Inverter Mode
  10. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  11. 5Trademarks
  12. 6About the Authors
  13. 7Revision History

2.3.1.2 LCL Filter Design

Any system of power transfer to the grid is required to meet certain output specifications for harmonic content. In voltage sourced systems like modern photo-voltaic inverters, a high-order LCL filter typically provides sufficient harmonic attenuation, along with reducing the overall design size versus a simpler filter design. However, due to the higher order nature, take some care in the design to control resonance. Figure 2-24 shows a typical LCL filter.

TIDA-01606 LCL Filter ArchitectureFigure 2-24 LCL Filter Architecture

One of the key benefits of using SiC MOSFETs (as this reference design does) is the ability to increase the switching frequency of the power stage significantly versus traditional Si-based switching elements. This increased switching frequency has a direct impact on the output filter resonant design of the inverter, which needs to be accounted for. To make sure that the filter is designed correctly around this switch frequency, this known mathematical model is used in this design.

The primary component is the inverter inductor, or Linv, which can be derived using Equation 28:

Equation 1. TIDA-01606

where,

  • fSW is the PWM switching frequency
  • Igrid_rated is the grid RMS current rating
  • % ripple is the ripple current percentage of the rated grid current

The sizing of the primary EMI filter capacitor, Cf, is determined by Equation 2:

Equation 2. 1 L i n v × ( 2 π × f S W ) 2 < < C f < % × Q r a t e d 2 π × f g r i d × V g r i d 2

where

  • % Qrated is the percentage of the rated reactive power to limit the Cf capacitor
  • Fgrid is the grid electrical frequency
  • Vgrid is the grid phase voltage

Equation 3 shows an example calculation:

Equation 3. 1 130 μ F × ( 2 π × 90 k H z ) 2 < < C f < 5 % × 11 k V A 3 2 π × 60 H z × 230 V 2 24 n F   < < C f <   9 . 2 μ F

In E7, 4.7 µF was selected for Cf. This equates to approximately 6.4 kHz for the cutoff frequency.