TIDUFE5 July   2025

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Terminology
    2. 1.2 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1  TMS320F2800137
      2. 2.3.2  LMG3651R025
      3. 2.3.3  LMG2650
      4. 2.3.4  TMCS1126
      5. 2.3.5  ISO6721
      6. 2.3.6  UCC28881
      7. 2.3.7  UCC27712
      8. 2.3.8  TPS562206
      9. 2.3.9  TLV9062
      10. 2.3.10 TLV74033
  9. 3System Design Theory
    1. 3.1 Totem Pole PFC
      1. 3.1.1 Inductor Ratings
      2. 3.1.2 AC Voltage Sensing
      3. 3.1.3 DC Link Voltage Sensing
      4. 3.1.4 AC Current Sensing
      5. 3.1.5 DC Link Capacitor Rating
    2. 3.2 Three-Phase PMSM Drive
      1. 3.2.1 Field Oriented Control of PM Synchronous Motor
        1. 3.2.1.1 Space Vector Definition and Projection
        2. 3.2.1.2 Clarke Transformation
        3. 3.2.1.3 Park Transformation
        4. 3.2.1.4 Basic Scheme of FOC for AC Motor
        5. 3.2.1.5 Rotor Flux Position
      2. 3.2.2 Sensorless Control of PM Synchronous Motor
        1. 3.2.2.1 Enhanced Sliding Mode Observer With Phase Locked Loop
          1. 3.2.2.1.1 Mathematical Model and FOC Structure of an IPMSM
          2. 3.2.2.1.2 Design of ESMO for the IPMSM
          3. 3.2.2.1.3 Rotor Position and Speed Estimation With PLL
      3. 3.2.3 Hardware Prerequisites for Motor Drive
        1. 3.2.3.1 Current Sensing With Three-Shunt
        2. 3.2.3.2 Motor Voltage Feedback
  10. 4Hardware, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
      1. 4.1.1 Hardware Board Overview
      2. 4.1.2 Test Conditions
      3. 4.1.3 Test Equipment Required for Board Validation
    2. 4.2 Test Setup
    3. 4.3 Test Results
      1. 4.3.1 Functional Waveforms
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 Bill of Materials
      3. 5.1.3 Altium Project
      4. 5.1.4 Gerber Files
      5. 5.1.5 PCB Layout Recommendations
    2. 5.2 Tools
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Author

3.2.3.2 Motor Voltage Feedback

Voltage feedback is needed in the FAST estimator to allow the best performance at the widest speed range, the phase voltages are measured directly from the motor phases instead of a software estimate. The eSMO relies on software estimation values to represent the voltage phases without using the motor phase voltage sensing circuit. This software value (USER_ADC_FULL_SCALE_VOLTAGE_V) depends on the circuit that senses the voltage feedback from the motor phases. Figure 3-21 shows how the motor voltage is filtered and scaled for the ADC input range using a voltage feedback circuit based on resistor dividers. The similar circuit is used to measure both compressor and fan motors, and the DC bus.

The maximum phase voltage feedback measurable by the microcontroller in this reference design can be calculated as given in Equation 50, considering the maximum voltage for the ADC input is 3.3V.

Equation 50. VFS=VADC_FS×Gv=3.3V×137.07=452.32V

where

  • Gv is attenuation factor which can be calculated from Equation 51
Equation 51. GV=R54+R59+R64+R71R71=332K+332K+332K+7.32K7.32K=137.07

With that voltage feedback circuit, the following setting is made in user_mtr1.h:

//! \brief Defines the maximum voltage at the AD converter
#define USER_M1_ADC_FULL_SCALE_VOLTAGE_V         (452.32f)

The voltage filter pole is needed by the FAST estimator to allow an accurate detection of the voltage feedback. The filter needs to be low enough to filter out the PWM signals, and at the same time allow a high-speed voltage feedback signal to pass through the filter. As a general guideline, a cutoff frequency of a few hundred Hz is enough to filter out a PWM frequency of 5 to 20kHz. The hardware filter needs to only be changed when ultra-high-speed motors are run, which generate phase-voltage frequencies in the order of a few kHz.

Use Equation 52 to calculate the filter pole setting in this reference design.

Equation 52. ffilter_pole=12×π×RParallel×C=466.01 Hzwhere, C=47nF RParallel = 332K+332K+332K×7.32K332K+332K+332K+7.32K=7.267kΩ 

The following code example shows how this is defined in user_mtr1.h:

//! \brief Defines the analog voltage filter pole location, Hz
#define USER_M1_VOLTAGE_FILTER_POLE_Hz           (466.01f)
TIDA-010282 Motor Voltage Sensing CircuitFigure 3-21 Motor Voltage Sensing Circuit