AN 995: Three-phase Boost Bidirectional AC-DC and LLC DC-DC Converter for EV Charging Design Example

ID 784593
Date 9/15/2023
Public
Document Table of Contents

3.2.2.3. Output Capacitor

A subblock emulates the output capacitor or DC-link capacitor, for which you must consider an acceptable output voltage ripple. In the continuous-time domain, you can use standard electronics formula to obtain the capacitor value.

Where:

  • ΔV = 0.5 V, which is the acceptable output voltage ripple.
  • 1 x 10-5s is the inverse of the switching frequency.
  • 125 A is the maximum output current.

The voltage across the output capacitor (VDC ) is the integral of the current flowing into it as follows:

The inductor and switch models calculate the high side current, which is a split between the output capacitor (IC ) and load resistor (ILOAD ). Although VC is controlled to a DC voltage, the voltage on the capacitor terminals is relative to the ground (VDC_P and VDC_N ) switches up and down with the PWM of the switches. The calculation of VDC_P and VDC_N depends on the state of the PWM signals (0 or 1).

Then, calculate VDC_P using: