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

3.2.1 Impact of Bandwidth

In this simulation, the dual active bridge with phase shift control is running at a switching frequency of 100 kHz and is configured as constant current source output that drives a fixed current of 20 A into a pure resistive 10-Ω load (that results in a 200-V DC output, representing a 4-kW load).

At time t1 = 2ms, the load is changed from 10 Ω to 20 Ω. This results in an immediate current change down to 10 A (since voltage is 200 V at that time). After some time, the control loop starts to regulate back to the 20-A constant current which forces the output voltage to increase to 400-V DC when settled (resulting in a load change from 4 kW to 2 kW). Figure 3-3 shows the transient response of the output current.

Figure 3-3 DC/DC Step Load Response vs Current Sensor Bandwidth

Figure 3-3 shows the response to the same load step for different bandwidth settings or the current sensor in the control loop. With a current sensor bandwidth of only 1 kHz, there is a long settling time of 1.6 ms. Increasing the bandwidth to 10 kHz and 100 kHz, brings the settling time (90% of end value) down to 0.6ms and 0.3ms, respectively. A further increase of current-sensor bandwidth does not improve the transient response significantly because the settling time is limited by the control-loop bandwidth of the current loop which was set to 10 kHz.

In conclusion, a current sensor at point E or F with a bandwidth lower than 100 kHz is sufficient to keep the settling time < 1ms for any load step change at the converter output.