SPRACM9B June   2019  – November 2020 F29H850TU , F29H859TU-Q1 , TMS320F28384D , TMS320F28384S , TMS320F28386D , TMS320F28386S , TMS320F28388D , TMS320F28388S , TMS320F28P650DH , TMS320F28P650DK , TMS320F28P650SH , TMS320F28P650SK , TMS320F28P659DH-Q1 , TMS320F28P659DK-Q1 , TMS320F28P659SH-Q1

 

  1.   Trademarks
  2. 1 Introduction
    1. 1.1 Acronyms Used in This Document
  3. 2 Benefits of the TMS320F2838x MCU for High-Bandwidth Current Loop
  4. 3 Current Loops in Servo Drives
  5. 4 Outline of the Fast Current Loop Library
  6. 5 Fast Current Loop Evaluation
    1. 5.1 Evaluation Setup
      1. 5.1.1 Hardware
      2. 5.1.2 Software
      3. 5.1.3 FCL With T-Format Type Position Encoder
        1. 5.1.3.1 Connecting T-Format Encoder to IDDK
        2. 5.1.3.2 T-Format Interface Software
        3. 5.1.3.3 T-Format Encoder Latency Considerations
      4. 5.1.4 SDFM
      5. 5.1.5 Incremental System Build
  7. 6 Incremental Build Level 1
    1. 6.1 SVGEN Test
    2. 6.2 Testing SVGEN With DACs
    3. 6.3 Inverter Functionality Verification
  8. 7 Incremental Build Level 2
    1. 7.1 Setting the Overcurrent Limit in the Software
    2. 7.2 Current Sense Method
    3. 7.3 Voltage Sense Method
    4. 7.4 Setting Current Regulator Limits
    5. 7.5 Verification of Current Sense
    6. 7.6 Position Encoder Feedback
      1. 7.6.1 Speed Observer and Position Estimator
      2. 7.6.2 Verification of Position Encoder Orientation
  9. 8 Incremental Build Level 3
    1. 8.1 Observation One – PWM Update Latency
      1. 8.1.1 From the Expressions Window
      2. 8.1.2 From the Scope Plot
  10. 9 Incremental Build Level 4
    1. 9.1 Observation
  11. 10Incremental Build Level 5
  12. 11Incremental Build Level 6
    1. 11.1 Integrating SFRA Library
    2. 11.2 Initial Setup Before Starting SFRA
    3. 11.3 SFRA GUIs
    4. 11.4 Setting Up the GUIs to Connect to Target Platform
    5. 11.5 Running the SFRA GUIs
    6. 11.6 Influence of Current Feedback SNR
    7. 11.7 Inferences
      1. 11.7.1 Bandwidth Determination From Closed Loop Plot
      2. 11.7.2 Phase Margin Determination From Open Loop Plot
      3. 11.7.3 Maximum Modulation Index Determination From PWM Update Time
      4. 11.7.4 Voltage Decoupling in Current Loop
    8. 11.8 Phase Margin vs Gain Crossover Frequency
  13. 12Incremental Build Level 7
    1. 12.1 Run the Code on CPU1 to Allocate ECAT to CM
    2. 12.2 Run the Code on CM to Setup ECAT
    3. 12.3 Setup TwinCAT
    4. 12.4 Scanning for EtherCAT Devices via TwinCAT
    5. 12.5 Program ControlCard EEPROM for ESC
    6. 12.6 Running the Application
  14. 13Incremental Build Level 8
    1. 13.1 Run the Code on CPU1 to Allocate ECAT to CM
    2. 13.2 Run the Code on CM to Setup ECAT
    3. 13.3 Running the Application
  15. 14References
  16. 15Revision History

11.3 SFRA GUIs

There are two GUIs available to perform the frequency response analysis, one (SFRA_GUI) to plot open loop and plant Bode diagram, and another (SFRA_GUI_MC) to plot open loop and closed loop Bode diagram. They can be invoked and connected to the target platform to study the control loops. The GUI executables are available in the location as mentioned in Section 11.1.

Double click on the choice of GUI executable and the GUI screen will appear as shown in Figure 11-2 for SFRA_GUI or in Figure 11-3 for SFRA_GUI_MC. They look almost identical, the difference is in the pull down menu under 'FRA Settings' starting with the label 'Open Loop'.

  • In the SFRA_GUI, this pull down menu helps to select between Open Loop Model and Plant Model.
  • In the SFRA_GUI_MC, this pull down menu helps to select between Open Loop Model and Closed Loop Model.
Note:

The GUIs interpretation of bandwidth is different.

  • In the SFRA_GUI, bandwidth is defined as the open loop gain cross over frequency
  • In SFRA_GUI_MC, bandwidth is defined according to Chinese standard GBT 16439-2009 and NEMA ICS 16 (Speed Loop) for servo drives. It defines bandwidth as the frequency where the closed loop output magnitude drops by 3dB or the phase shift lag exceed 90° for the speed loop. It is suggestive that bandwidth is the frequency where the first of these two instances would occur. This approach is used to analyze current loops as well in this demo.

This demo uses the GUI 'SFRA_GUI_MC'. However, you are encouraged to experiment with the other GUI as well to study the plant. With the SFRA_GUI, you can plot the same graph as in SFRA_GUI_MC by passing the argument 'SFRA_GUI_PLOT_GH_CL' in the function configureSFRA(), as shown in the code snippet below.

configureSFRA(SFRA_GUI_PLOT_GH_CL, ISR_FREQUENCY);   // to plot GH and CL plots using SFRA_GUI

But the inferences from the plots are not according to that in SFRA_GUI_MC. Therefore, it is advised to configure SFRA for 'SFRA_GUI_PLOT_GH_H' so that you can see open loop, closed loop and plant model plots using these two GUIs, by using one at a time. For digital power applications, SFRA_GUI_MC inferences may not apply and so SFRA_GUI can be used to display closed loop plots as well.

GUID-9820FB4E-A637-4CB3-9240-E9367D3874A4-low.pngFigure 11-2 SFRA GUI
GUID-452163A4-E9D4-490F-B579-6757E4CBD01D-low.pngFigure 11-3 SFRA GUI MC