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

2.2.1.2 Transient Analysis: Step Power and Voltage Sag Response

This section analyzes the performance of the control current loops with the aim of determining the minimum bandwidth of the current-sensing stage when transients caused by the grid are injected. The goal of the study is to find the minimum bandwidth allowed to keep the converter tied to the grid when no major malfunctions are present in the PCC without running in overcurrent protection status. Multiple stress scenarios which can cause overcurrents were analyzed: AC voltage sag, step-power response, and AC overvoltage. Between the mentioned faults, only voltage sag and step-power response are explained.

Figure 2-8 depicts switching node currents (Point B) with respect to grid voltages when a converter operating with sensors has a bandwidth of 6 kHz. In the top graph, the output power of the AC/DC converter is stepped from zero to 11 kW at 3ms, resulting in an overcurrent in L1 (I_L1_B). In the bottom graph, the AC line voltage is dropped by 20% at 26ms, resulting in significant overcurrent in L2 (I_L2_B) that can lead to an unwanted converter shut-down.

Figure 2-8 Grid Voltages and Currents of AC/DC Converter: Step Power and Voltage Sag Responses

Multiple simulations were run by only changing the bandwidth of the current sensor (6 kHz, 30 kHz, 60 kHz), then comparing of the peak overcurrent in the switching node when a step power is requested by the battery. Figure 2-9 shows the results of the simulations. With a 6-kHz current sensor, the current in L1 overshoots by 30% (33-A peak) relative to the prime transient response that is achieved with a 30-kHz current sensor (10 times higher than the bandwidth of the current control loop). An additional increase in current-sensing bandwidth (from 30 kHz to 60 kHz) brings no additional benefit because both the curves overlap.

Figure 2-9 shows the zoomed-in portion at t = 3 ms (span 200 μs) of the step power response (11 kW) of the AC/DC converter with the current-sensor bandwidth as the parameter.

Figure 2-9 Zoomed Portion at t = 3ms (Span 200μs)

Multiple simulations were run by only changing the bandwidth of the current sensor. Comparisons of the peak current in the switching node when the converter is working at full load and unpredictable voltage sag on the grid occurs were conducted. Figure 2-10 shows the line-transient response with 6 kHz, 30 kHz, and 60 kHz current sensors. With a 6-kHz current sensor, the current in L2 overshoots by > 2 A (to an approximate 33-A peak) relative to the prime transient response that is achieved with a 30-kHz current sensor (10 times higher than the bandwidth of the current control loop). An additional increase in current-sensing bandwidth (from 30 kHz to 60 kHz) brings no additional benefit (both curves overlap).

Figure 2-10 shows the zoomed-in portion at t = 26ms (span 200μs) of the AC/DC converter voltage sag response with the current-sensor bandwidth as the parameter.

Figure 2-10 Zoomed Portion at t = 26ms (Span 200μs)

To take full advantage of the available current control loop bandwidth, keep the sensing bandwidth at least 10 times higher than the control loop bandwidth. By applying this guideline, the resolution of the current measurement is maximized because measurement range does not have to be sacrificed for overcurrent detection.