SBAA541 December   2022 AMC1202 , AMC1302 , AMC1306M05 , AMC22C11 , AMC22C12 , AMC23C10 , AMC23C11 , AMC23C12 , AMC23C14 , AMC23C15 , AMC3302 , AMC3306M05

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 DC Charging Station for Electric Vehicles
    2. 1.2 Current-Sensing Technology Selection and Equivalent Model
      1. 1.2.1 Sensing of the Current With Shunt-Based Solution
      2. 1.2.2 Equivalent Model of the Sensing Technology
  4. 2Current Sensing in AC/DC Converters
    1. 2.1 Basic Hardware and Control Description of AC/DC
      1. 2.1.1 AC Current Control Loops
      2. 2.1.2 DC Voltage Control Loop
    2. 2.2 Point A and B – AC/DC AC Phase-Current Sensing
      1. 2.2.1 Impact of Bandwidth
        1. 2.2.1.1 Steady State Analysis: Fundamental and Zero Crossing Currents
        2. 2.2.1.2 Transient Analysis: Step Power and Voltage Sag Response
      2. 2.2.2 Impact of Latency
        1. 2.2.2.1 Fault Analysis: Grid Short-Circuit
      3. 2.2.3 Impact of Gain Error
        1. 2.2.3.1 Power Disturbance in AC/DC Caused by Gain Error
        2. 2.2.3.2 AC/DC Response to Power Disturbance Caused by Gain Error
      4. 2.2.4 Impact of Offset
    3. 2.3 Point C and D – AC/DC DC Link Current Sensing
      1. 2.3.1 Impact of Bandwidth on Feedforward Performance
      2. 2.3.2 Impact of Latency on Power Switch Protection
      3. 2.3.3 Impact of Gain Error on Power Measurement
        1. 2.3.3.1 Transient Analysis: Feedforward in Point D
      4. 2.3.4 Impact of Offset
    4. 2.4 Summary of Positives and Negatives at Point A, B, C1/2 and D1/2 and Product Suggestions
  5. 3Current Sensing in DC/DC Converters
    1. 3.1 Basic Operation Principle of Isolated DC/DC Converter With Phase-Shift Control
    2. 3.2 Point E, F - DC/DC Current Sensing
      1. 3.2.1 Impact of Bandwidth
      2. 3.2.2 Impact of Gain Error
      3. 3.2.3 Impact of Offset Error
    3. 3.3 Point G - DC/DC Tank Current Sensing
    4. 3.4 Summary of Sensing Points E, F, and G and Product Suggestions
  6. 4Conclusion
  7. 5References

3.2.2 Impact of Gain Error

Current sensors have gain error that may impact on the accuracy of the control loop. A simulation with the current sensor model from Figure 1-2 is performed to study the settling time at turn-on of the converter. The bandwidth of the sensor is set to 100 kHz and gain errors of 0%, 1%, and 2% are chosen. Figure 3-4 show the impact of the errors.

Figure 3-4 Steady State Output Current Errors vs Current Sensor Gain Errors

Settling time after a load change is quite similar since the bandwidth of the sensor is defining the settling time for all cases, meaning the gain error does not impact settling time significantly. But the gain error impacts the value to which the output current settles. This simulation shows that the remaining constant error at the output current is about 0.66% (about 0.15 A) below the ideal 20 A if the current sensor has gain error of 1% (about 1.33% / 0.32 A below the ideal 20-A output current if the current sensor has a gain error 2% respectively).

The gain error is defined as the error relative to full-scale of the current. In our example the full-scale current is 32 A. This means for a 20-A current, the resulting gain error is only about two thirds of the full-scale (about 0.66%). For a 2% full scale error, the remaining output current error settles at about 1.33%.

If the output current needs to settle within a 1% window, the full-scale gain error of a current sensor must not be bigger than 1%.