SPRACT7 August   2020 TMS320F280021 , TMS320F280021-Q1 , TMS320F280023 , TMS320F280023-Q1 , TMS320F280023C , TMS320F280025 , TMS320F280025-Q1 , TMS320F280025C , TMS320F280025C-Q1 , TMS320F280040-Q1 , TMS320F280040C-Q1 , TMS320F280041 , TMS320F280041-Q1 , TMS320F280041C , TMS320F280041C-Q1 , TMS320F280045 , TMS320F280048-Q1 , TMS320F280048C-Q1 , TMS320F280049 , TMS320F280049-Q1 , TMS320F280049C , TMS320F280049C-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Fundamental Theories of FOC and Current Measurement
    1. 2.1 Basic Theory of FOC
    2. 2.2 Current Sensing Technique
      1. 2.2.1 Low-Side Current Measurement
        1. 2.2.1.1 Three-Shunt Current Sensing
        2. 2.2.1.2 Dual-Shunt Current Sensing
        3. 2.2.1.3 Single-Shunt Current Sensing
  5. 3Implementation of Single-Shunt Phase Current Reconstruction
    1. 3.1 Duty Cycle Compensation
    2. 3.2 PWM Phase Shift Compensation
    3. 3.3 Current Reconstruction
  6. 4Sensorless FOC With Single-Shunt Measurement
  7. 5Hardware Consideration for Single-Shunt Current Sensing
    1. 5.1 Slew Rate
    2. 5.2 Current Sensing Circuit
  8. 6Test Results
  9. 7Summary
  10. 8References

3 Implementation of Single-Shunt Phase Current Reconstruction

As previously mentioned, the active voltage vectors must be long enough to reliably measure the dc link current during every PWM switching interval. In case the active vector duration is less than the minimum duration in Equation 2, PWM duty should be modified to ensure measurement time. This application report describes two methods for PWM compensation:

  • The first solution is duty cycle compensation which keeps a symmetric PWM.
  • The second solution is phase shift compensation that keeps average output voltage.