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

4 Sensorless FOC With Single-Shunt Measurement

The sensorless observer, which is called as FAST™, integrated in F28004xC and F28002xC was upgraded to version 2.0 with MotorControl SDK. The new version of FAST was implemented with floating point. It improves the accuracy of parameter estimation and the sensorless performance at low speed.

The current reconstruction algorithm and PWM phase shift compensation for single-shunt measurement was implemented and verified with MotorControl SDK. As shown in Figure 4-1, two new modules have been added. The first one is the module for three-phase current reconstruction from sampled dc link current by using space vector’s sector information. The second one is the module for PWM compensation to get high enough active vector duration in unmeasurable area. In this module, CMPC and CMPD in ePWM type-4 were selected as ADC SOC trigger sources for sampling dc link current.

GUID-20200819-CA0I-FHK5-NVMG-WDBMQCHBQTNV-low.png Figure 4-1 Flowchart of Main Control Loop With Single-Shunt for Sensorless-FOC

Figure 4-2 shows the function of PWM compensation, which is called from main control loop shown in Figure 4-1, for single shunt by using C2000™ device drivers in C2000Ware. This function calls PWM Phase Shift Compensation (DCLINK_SS_pwmCompensation) function as shown in Figure 3-4.

GUID-20200819-CA0I-PF4L-NHVV-NWZFQK3NVRB3-low.png Figure 4-2 Flowchart of HAL_singleShuntCompensation Function

Figure 4-3 shows the timing diagram for ADC sampling and ADC interrupt. CMPC and CMPD in ePWM type-4 were selected as ADC SOC trigger sources for sampling dc link current. So, CMPC and CMPD values are updated every cycle based on shifted PWM CMPB value. Because InstaSPIN-FOC solution needs phase voltage measurement, phase output voltages (Va, Vb, Vc) and dc link voltage are sampled at ePWM1 zero counter. The interrupt service routine (ISR) is triggered by the end of conversion (EOC) of the ADC. In the ISR, the current information measured on the PWM down counter prior to one cycle is used for current control.

GUID-20200819-CA0I-WTKM-NXX2-MCB0CK9H8TGD-low.png Figure 4-3 Timing Diagram of ADC Sampling and ADC Interrupt