SPRACM9B June   2019  – November 2020 TMS320F28384D , TMS320F28384S , TMS320F28386D , TMS320F28386S , TMS320F28388D , TMS320F28388S , TMS320F28P650DH , TMS320F28P650DK , TMS320F28P650SH , TMS320F28P650SK , TMS320F28P659DK-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

1 Introduction

The concept of FOC of AC drives is well known and is already outlined in many earlier documents from TI. Modern AC servo drives, depending on the end application, need high-bandwidth current control and speed control to enable superior performance, such as in CNC machines or in fast and precision control applications. Because of the highly time critical computational burden of these systems and the need for flexible PWMs, a combination of FPGAs, fast external ADCs, and multiple MCUs are used by many designers.

With the TMS320F2838x MCU, due to its higher level of integration, it is possible to implement fast current loop (FCL) algorithms that provide a high current loop bandwidth with the same external hardware as used in classical FOC methods. TI has developed the FCL algorithm on this MCU and implemented it on the Design DRIVE IDDK platform.

With a 10-kHz PWM carrier, the current loop gain crossover frequency is expected to exceed 3 kHz, and the closed loop bandwidth is expected at about 5 KHz (per NEMA ICS 16 and Chinese GBT 16439-2009 guidelines) and the maximum duty cycle is expected to be approximately 96%. Using TI's Software Frequency Response Analyzer (SFRA) library, frequency response analysis of the current loops can be performed in real time to verify the above benchmarks. Dynamic frequency response analysis in real-time on a motor drive system is unique among MCU suppliers and is currently capable only on C2000 MCUs.

Due to the presence of a configurable logic block (CLB), it is now possible to implement custom interface logics for various absolute encoders that utilize various protocols such as EnDAT, BiSS, T-format, and so forth, without external logics or FPGAs.

Besides control, TMS320F2838x MCU has an Arm Cortex-M4 based Connectivity Manager and an EtherCAT Slave Control peripheral. This helps to seamlessly integrate control and communication in a single chip to enable development of cost effective solutions for industrial servo drives.

This document evaluates the implementation of FCL algorithms on C2000 devices, studies the frequency response analysis of current loops in real time, verifies the interface logics for T-format encoder using on-chip configurable logic blocks (CLB) and also performs EtherCAT communication with a master to serve as a connected drive. The position loop can be closed using a QEP encoder or a T-format encoder and FCL can be implemented in both cases. Quantitative test results from frequency response analysis are discussed.