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

5.1.4 SDFM

High-resolution, accurate, isolated phase current measurement is vital in automotive traction and servo drive applications, where high-performance torque and motion control are required. The options available for phase-current measurement are to use Hall-effect sensors, flux-gate sensors, current transformers, and shunt resistors. The first three options have inherent galvanic isolation benefits and a high current measurement range, but the linearity, bandwidth, and drift are of lower performance when compared to the shunt-resistor option. Shunt resistors provide a highly linear, high-bandwidth, and cost-effective measurement solution. Reinforced isolation provides both benefits of isolation and high linearity and bandwidth. Isolated shunt-based current measurement is accomplished either by using an isolated amplifier or an isolated delta-sigma modulator.

Figure 5-1 shows the mechanism of phase current sensing in servo drive motors, there are two paths implemented in the design, the high-speed bit stream output from the isolated modulators is filtered by TI's C2000 family real-time controllers that have a built-in sigma-delta filter module (SDFM), allowing the user to fine-tune signal bandwidth and accuracy. The SDFM is a four-channel digital filter designed specifically for current measurement in motor control applications. Each channel can receive an independent delta-sigma modulator bit stream which is processed by four individually programmable digital decimation filters. The filters include a fast comparator for immediate digital threshold comparisons for over-current and undercurrent monitoring. Also, a filter-bypass mode is available to enable data logging, analysis, and customized filtering. The SDFM pins are configured using the GPIO multiplexer. A key benefit of the SDFM is it enables a simple, cost-effective, and safe high-voltage isolation boundary.

GUID-4BDA38AD-4B1E-4FFB-9008-A358A5A834FF-low.gif Figure 5-1 Current Sense Using Delta-Sigma Modulator in Servo Drive

On the IDDK board, the voltage across the shunt resistor is fed into the AMC1304M25 sigma-delta modulator, which generates the sigma-delta stream that is decoded by the SDFM demodulator present on the C2000 MCU. The clock for the modulator is generated from the EPWM5 module on the C2000 MCU, and the AMC1304M25 data is decided using the built-in SDFM modulator.

To select the shunt-resistor based current sense with SDFM by setting the configuration in fcl_f2838x_tmdxiddk_settings_cpu1.h as shown below.

#define  CURRENT_SENSE       SD_CURRENT_SENSE