TIDUD61E October   2020  – April 2021

 

  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 Input AC Voltage Sensing
      2. 2.2.2 Bus Voltage Sensing
      3. 2.2.3 AC Current Sensing
      4. 2.2.4 Sense Filter
      5. 2.2.5 Protection (CMPSS)
    3. 2.3 Highlighted Products
      1. 2.3.1 C2000™ MCU F28004x
      2. 2.3.2 LMG3410R070
      3. 2.3.3 UCC27714
    4. 2.4 System Design Theory
      1. 2.4.1 PWM
      2. 2.4.2 Current Loop Model (PFC and Inverter mode)
      3. 2.4.3 DC Bus Regulation Loop (for PFC mode only)
      4. 2.4.4 Soft Start Around Zero Crossing for Eliminate or Reduce Current Spike
      5. 2.4.5 AC Drop Test
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
        1. 3.1.1.1 Base Board Settings
        2. 3.1.1.2 Control Card Settings
      2. 3.1.2 Software
        1. 3.1.2.1 Opening Project Inside CCS
        2. 3.1.2.2 Project Structure
        3. 3.1.2.3 Using CLA on C2000 MCU to Alleviate CPU Burden
        4. 3.1.2.4 CPU and CLA Utilization and Memory Allocation
        5. 3.1.2.5 Running the Project
          1. 3.1.2.5.1 Lab 1: Open Loop, DC (PFC Mode)
            1. 3.1.2.5.1.1 Setting Software Options for LAB 1
            2. 3.1.2.5.1.2 Building and Loading Project
            3. 3.1.2.5.1.3 Setup Debug Environment Windows
            4. 3.1.2.5.1.4 Using Real-Time Emulation
            5. 3.1.2.5.1.5 Running Code
          2. 3.1.2.5.2 Lab 2: Closed Current Loop DC (PFC)
            1. 3.1.2.5.2.1 Setting Software Options for Lab 2
            2. 3.1.2.5.2.2 Designing Current Loop Compensator
            3. 3.1.2.5.2.3 Building and Loading Project and Setting up Debug
            4. 3.1.2.5.2.4 Running Code
          3. 3.1.2.5.3 Lab 3: Closed Current Loop, AC (PFC)
            1. 3.1.2.5.3.1 Setting Software Options for Lab 3
            2. 3.1.2.5.3.2 Building and Loading Project and Setting up Debug
            3. 3.1.2.5.3.3 Running Code
          4. 3.1.2.5.4 Lab 4: Closed Voltage and Current Loop (PFC)
            1. 3.1.2.5.4.1 Setting Software Options for Lab 4
            2. 3.1.2.5.4.2 Designing Voltage Loop Compensator
            3. 3.1.2.5.4.3 Building and Loading Project and Setting up Debug
            4. 3.1.2.5.4.4 Running Code
          5. 3.1.2.5.5 Lab 5: Open loop, DC (Inverter)
            1. 3.1.2.5.5.1 Setting Software Options for Lab 5
            2. 3.1.2.5.5.2 Building and Loading Project
            3. 3.1.2.5.5.3 Setup Debug Environment Windows
            4. 3.1.2.5.5.4 Running Code
          6. 3.1.2.5.6 Lab 6: Open loop, AC (Inverter)
            1. 3.1.2.5.6.1 Setting Software Options for Lab 6
            2. 3.1.2.5.6.2 Building and Loading Project and Setting up Debug
            3. 3.1.2.5.6.3 Running Code
          7. 3.1.2.5.7 Lab 7: Closed Current Loop, DC (Inverter with resistive load)
            1. 3.1.2.5.7.1 Setting Software Options for Lab 7
            2. 3.1.2.5.7.2 Designing Current Loop Compensator
            3. 3.1.2.5.7.3 Building and Loading Project and Setting up Debug
            4. 3.1.2.5.7.4 Running Code
          8. 3.1.2.5.8 Lab 8: Closed Current Loop, AC (Inverter with resistive load)
            1. 3.1.2.5.8.1 Setting Software Options for Lab 8
            2. 3.1.2.5.8.2 Building and Loading Project and Setting up Debug
            3. 3.1.2.5.8.3 Running Code
          9. 3.1.2.5.9 Lab 9: Closed Current Loop (Grid Connected Inverter)
            1. 3.1.2.5.9.1 Setting Software Options for Lab 9
            2. 3.1.2.5.9.2 Building and Loading Project and Setting up Debug
            3. 3.1.2.5.9.3 Running Code: Emulated Grid-tied Condition (Verification purpose only)
            4. 3.1.2.5.9.4 Running Code: Grid-tied Condition
        6. 3.1.2.6 Running Code on CLA
        7. 3.1.2.7 Advanced Options
          1. 3.1.2.7.1 Input Cap Compensation for PF Improvement Under Light Load
          2. 3.1.2.7.2 83
          3. 3.1.2.7.3 Adaptive Dead Time for Efficiency Improvements
          4. 3.1.2.7.4 Phase Shedding for Efficiency Improvements
          5. 3.1.2.7.5 Non-Linear Voltage Loop for Transient Reduction
          6. 3.1.2.7.6 Software Phase Locked Loop Methods: SOGI - FLL
    2. 3.2 Testing and Results
      1. 3.2.1 Test Results at Input 120 Vrms, 60 Hz, Output 380-V DC
        1. 3.2.1.1 Startup
        2. 3.2.1.2 Steady State Condition
        3. 3.2.1.3 Transient Test With Step Load Change
          1. 3.2.1.3.1 0% to 50% Load Step Change
          2. 3.2.1.3.2 50% to 100% Load Step Change
          3. 3.2.1.3.3 100% to 50% Load Step Change
          4. 3.2.1.3.4 50% to 100% Load Step Change
      2. 3.2.2 Test Results at Input 230 Vrms, 50 Hz, Output 380 V DC
        1. 3.2.2.1 Startup
        2. 3.2.2.2 Steady State Condition
        3. 3.2.2.3 Transient Test With Step Load Change
          1. 3.2.2.3.1 33% to 100% Load Step Change
          2. 3.2.2.3.2 100% to 33% Load Step Change
      3. 3.2.3 Test Results Graphs
  9. 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
  10. 5Software Files
  11. 6Related Documentation
    1. 6.1 Trademarks
  12. 7About the Author
  13. 8Revision History

2.4.4 Soft Start Around Zero Crossing for Eliminate or Reduce Current Spike

Zero crossing current spikes is a challenging issue for TTPL PFC topologies. This issue is solved by implementing a soft start scheme with a state machine to turn on and off switches in a particular sequence.

GUID-DF8928B6-72BD-4A97-A963-91AA3F252DA0-low.gifFigure 2-13 PWM Sequence With Soft Starting to Reduce Current Spike at Zero Crossing

Figure 2-13 shows the switching sequence when the AC wave goes from negative to positive. During the negative half Q1 is ON, Q3 is the active FET, and Q4 is the sync FET. During this time the voltage across Q2 is the DC bus voltage. When the AC cycle changes, Q2 must be on 100% or close to 100%. If Q2 is turned ON immediately, a huge positive spike results. Therefore, a soft-start sequence is used to turn Q4 ON as shown in Figure 2-13. The tuning of this soft start depends on the inductance value and other power stage parameters such as device Coss.

Another reason for a negative current spike around zero crossing is the relatively low AC voltage around the zero crossing. When Q3 is turned ON, though the duty cycle is low, a high-voltage difference is applied and can result in a high negative current spike. Therefore, a sufficient delay is applied before Q3 starts switching back again.

Similarly, Q2 is turned on after some delay after the soft start has started.