JAJU879 November   2022

 

  1.   概要
  2.   リソース
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1System Description
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 TMS320F280039C
      2. 2.3.2 UCC21530-Q1
      3. 2.3.3 OPA607-Q1
      4. 2.3.4 LM25184-Q1
      5. 2.3.5 TCAN1044A-Q1
    4. 2.4 System Design Theory
      1. 2.4.1 Three-Phase PMSM Drive
      2. 2.4.2 Field Oriented Control of PM Synchronous Motor
      3. 2.4.3 Field Weakening (FW) and Maximum Torque Per Ampere (MTPA) Control
      4. 2.4.4 Compressor Drive with Automatic Vibration Compensation
      5. 2.4.5 Hardware Prerequisites for Motor Drive
        1. 2.4.5.1 Motor Current Feedback
          1. 2.4.5.1.1 Current Sensing with Three-Shunt
          2. 2.4.5.1.2 Current Sensing with Single-Shunt
        2. 2.4.5.2 Motor Voltage Feedback
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
      1. 3.1.1 Hardware Board Overview
      2. 3.1.2 Test Conditions
      3. 3.1.3 Test Equipment Required for Board Validation
    2. 3.2 Test Setup
      1. 3.2.1 Hardware Setup
      2. 3.2.2 Software Setup
        1. 3.2.2.1 Code Composer Studio Project
        2. 3.2.2.2 Software Structure
    3. 3.3 Test Procedure
      1. 3.3.1 Level 1 Incremental Build
        1. 3.3.1.1 Project Setup
        2. 3.3.1.2 Running the Application
      2. 3.3.2 Level 2 Incremental Build
        1. 3.3.2.1 Project Setup
        2. 3.3.2.2 Running the Application
      3. 3.3.3 Level 3 Incremental Build
        1. 3.3.3.1 Project Setup
        2. 3.3.3.2 Running the Application
      4. 3.3.4 Level 4 Incremental Build
        1. 3.3.4.1 Project Setup
        2. 3.3.4.2 Running the Application
        3. 3.3.4.3 Tuning Field Weakening and MTPA Control
        4. 3.3.4.4 Tuning Vibration Compensation
        5. 3.3.4.5 CAN FD Command Interface
    4. 3.4 Test Results
      1. 3.4.1 MCU CPU Load, Memory, and Peripheral Usage
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 サポート・リソース
    5. 4.5 Trademarks
2.4.5.1.1 Current Sensing with Three-Shunt

The current through the motor is sampled by the microcontroller as part of the motor control algorithm during every PWM cycle. To measure bidirectional currents of the motor phase, that is, positive and negative currents, the circuits below require a reference voltage of 1.65-V. This offset reference voltage is created by a voltage follower as shown in Figure 2-17. This 1.65-V reference voltage is used to both three-shunt and single-shunt AC voltage feedback sensing circuit.

Figure 2-17 1.65-V Reference from 3.3-V Input Circuit

Figure 2-18 shows how the motor current is represented as a voltage signal, with filtering, amplification, and offset to the center of the ADC input range. This circuit is used for each phase of the 3-phase PMSM of compressor and fan. The transfer function of this circuit is given by Equation 29.

Equation 29. VOUT=VOFFSET+IIN×RSHUNT×Gi

Where Rshunt=0.005(OHM) and Voffset=1.65(V)

The calculated resistance values lead to the sensing circuit shown in Figure 2-18, the Gi is given by Equation 30.

Equation 30. G i = R f b R i n = R 29 R 31 = 10 K 1 K = 10

The maximum peak to peak current measurable by the microcontroller is given by Equation 31.

Equation 31. I s c a l e _ m a x = V A D C _ m a x R s h u n t × G i = 3 . 3 0 . 005 × 10 = 66 A

which is the peak to peak value of ±33A. The following code snippet shows how this is defined for compressor motor in user_mtr1.h file:

//! \brief Defines the maximum current at the AD converter
//!
#define USER_M1_ADC_FULL_SCALE_CURRENT_A         (66.00f)

Correct polarity of the current feedback is also important so that the microcontroller has an accurate current measurement. In this hardware board configuration, the negative pin of the shunt resistor, which is connected to ground, is also connected to the non-inverting pin of the operational amplifier.

Figure 2-18 Motor Current Sensing Circuit with Three-Shunt