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

2.4 Summary of Positives and Negatives at Point A, B, C1/2 and D1/2 and Product Suggestions

Power switches are the most sensitive components that can be damaged by overload or overcurrent. The close proximity of power switches allows faster fault detection, leading to have sensing in B and C vitally important. For point B, the high-side power supply of the isolated amplifier can be shared with the high-side gate driver supply and fast overcurrent (OC) detection is possible. The current sensing at point B needs to be able to handle high Common Mode Transient Immunity (CMTI) and this measurement can get affected by noise during power-stage switching, in particular when GaN or SiC designs are adopted. The precise reactive power control is the best possible at point A, where the measurement is behind the filter far away from switching noise. The drawback is the requirement of an isolated power supply at point A. Only slow OC detection is possible. Table 2-1 summarizes the pros and cons of the various current-sensing points. Table 2-2 summarizes requirements and provides an excellent choice of products for each point.

Table 2-1 Positives and Negatives of the Current-Sensing Points A, B, C1/2, and D1/2
ABC1D1C2D2
Accurate power regulation(+)(1)(–)(+)(+)(++)(++)
Feedforward loopN/AN/A(–)(–)(+)(+)
Fault protection(–)(++)(++)(+)(–)(–)
Sharing

of power supply

(–)(+)(+)(–)(2)(+)(–)(2)
(1) Precise reactive power control at PCC is possible – accuracy to be defined by the manufacturer (often < 1%)
(2) D1 and D2 need a floating supply above VDC+
Table 2-2 AC/DC Minimum Requirements and Available Products for Current Sensing at Points A, B, C1/2, and D1/2
I-Sensing PointPrimary

Applications

Iso-Supply VoltageMinimum BandwidthMaximum Latency

Requested

CMTI		Minimum Accuracy(1)TI Products
(ISO-)AMP|
ISO-ΔΣ
AAble to adjust precisely reactive power

Floating needed

(ISO-VDD1)

> 102 kHz-Low< 3.7 %AMC3302| AMC3306M05
BOvercurrent protection and controlFrom upper gate driver> 102 kHz< 3.5 µsHigh< 3.7 %AMC1302 | AMC1306M05 | AMC23Cxx
C1Current in neg branch and fault detectionFrom lower gate driver-< 1.5 µsLow<1 %AMC1302 |AMC1306M05

| AMC3302 | AMC23Cxx| AMC22Cxx

D1Current in positive branch and fault detectionFloating above VDC+ needed-< 1.5 µsLow<1 %AMC3306M05

|AMC3302 | AMC23Cxx| AMC22Cxx

C2Current in neg branch

and fault detection

From lower Gate Driver> 6 kHz-Low<1 %AMC1302| AMC1306M05|AMC3302
D2Current in positive branch

and fault protection

Floating above VDC+ needed> 6 kHz-Low<1 %AMC3302| AMC3306M05| AMC23Cxx| AMC22Cxx
(1) 1% accuracy is only required in cases where it is necessary to measure the power precisely. 3% is sufficient for systems that do not require accurate power control.