Fundamentals of Power Electronics 1 Chapter 20: Quasi-Resonant Converters Chapter 20 Quasi-Resonant Converters Introduction 20.1The zero-current-switching quasi-resonant switch cell Waveforms of the half-wave ZCS quasi-resonant switch cell The average terminal waveforms The full-wave ZCS quasi-resonant switch cell 20.2Resonant switch topologies The zero-voltage-switching quasi-resonant switch The zero-voltage-switching multiresonant switch Quasi-square-wave resonant switches 20.3Ac modeling of quasi-resonant converters 20.4Summary of key points

Fundamentals of Power Electronics 2 Chapter 20: Quasi-Resonant Converters A test to determine the topology of a resonant switch network Replace converter elements by their high-frequency equivalents: Independent voltage source V g : short circuit Filter capacitors: short circuits Filter inductors: open circuits The resonant switch network remains. If the converter contains a ZCS quasi-resonant switch, then the result of these operations is

Fundamentals of Power Electronics 3 Chapter 20: Quasi-Resonant Converters Waveforms of the half-wave ZCS quasi-resonant switch cell The half-wave ZCS quasi-resonant switch cell, driven by the terminal quantities  v 1 (t)  Ts and  i 2 (t)  Ts. Conversion ratio Half wave Full wave ZCS boundary Peak transistor current Peak transistor voltage V 1 (same as PWM)

Fundamentals of Power Electronics 4 Chapter 20: Quasi-Resonant Converters Characteristics of the half-wave ZCS resonant switch J s ≤ 1 Switch characteristics: Mode boundary:

Fundamentals of Power Electronics 5 Chapter 20: Quasi-Resonant Converters Full-wave cell: switch conversion ratio µ Full-wave case: P 1 can be approximated as so

Fundamentals of Power Electronics 6 Chapter 20: Quasi-Resonant Converters The zero-voltage-switching quasi-resonant switch cell When the previously-described operations are followed, then the converter reduces to A full-wave version based on the PWM buck converter: half

Fundamentals of Power Electronics 7 Chapter 20: Quasi-Resonant Converters Zero-voltage switching quasi-resonant switch Conversion ratio Half wave Full wave ZCS boundary Peak transistor current Peak transistor current I T (same as PWM)

Fundamentals of Power Electronics 13 Chapter 20: Quasi-Resonant Converters Waveforms of the half-wave ZVS quasi-resonant switch cell

Fundamentals of Power Electronics 14 Chapter 20: Quasi-Resonant Converters Averaging the switch network waveforms

Fundamentals of Power Electronics 15 Chapter 20: Quasi-Resonant Converters Averaging capacitor voltage

Fundamentals of Power Electronics 16 Chapter 20: Quasi-Resonant Converters The average output voltage

Fundamentals of Power Electronics 17 Chapter 20: Quasi-Resonant Converters Results: Quasi-resonant switches

Fundamentals of Power Electronics 18 Chapter 20: Quasi-Resonant Converters Output characteristics: Full-wave ZVS buck

Fundamentals of Power Electronics 19 Chapter 20: Quasi-Resonant Converters Zero-current switching at turn-off of diode ZVS quasi-resonant buck example (Fig. 20.2)

Fundamentals of Power Electronics 20 Chapter 20: Quasi-Resonant Converters Transistor voltage stress in ZVS quasi-resonant switch converter