Quasi resonant converter

Soft-Switching Techniques

• Hard-switching: Involves switching devices on and off while voltage (V) and current (I) are non-zero during turn-on and turn-off, leading to:

  • Switching Losses: Energy is wasted during the switching process due to the overlap of V and I.
  • High Switching Noise: Rapid changes in V/I create electromagnetic interference.
  • Potential Device Damage: Overshoot in voltage or current can damage devices.

• Soft-switching: Reduces switching losses and noise by introducing inductors and capacitors:

  • Zero Voltage Switching (ZVS): Achieved when the voltage is zero at the turn-on point.
  • Zero Current Switching (ZCS): Achieved when the current is zero at the turn-off point.
  • A resonant circuit is typically required to facilitate soft-switching.

Classifications of Soft-Switching Techniques

• Types of Circuits:
  • Zero Voltage Switching Circuits
  • Zero Current Switching Circuits
• Historical Development:
  • Quasi-resonant converters
  • Resonant converters
  • Zero-switching PWM circuits
  • Zero-transition PWM circuits
  • Resonant DC-link inverters

Quasi-Resonant Converters

• Definition: A converter utilizing a quasi-sinusoidal waveform leading to significant voltage peaks:

  • Requires high withstand voltage devices due to high peak voltages.
  • Results in reactive power circulation, causing conduction losses.
  • Pulse Frequency Modulation (PFM) is used due to the fluctuating resonant period influenced by input voltage and load.

• Quasi Resonant Buck Converter:

  • Operated under Zero Current Switching (ZCS).
  • Topologies: Includes several operational modes (S on/off, D on/off).

Operation Modes of Quasi-Resonant Buck Converter

1. Mode 1: S on, D on

   • No current in resonant inductor or voltage across resonant capacitor, diode conducts all output current.
   • Voltage relationship: V = L{r} rac{di{L}}{dt}
   • Current at t2: i{L}(t) = rac{V{s}}{L_{r}} t

2. Mode 2: S on, D off

   • When diode D is reverse-biased, the capacitor starts charging.
   • Voltage and current equations for resonant elements involved in this mode are presented.

3. Mode 3: S off, D off

   • The capacitor discharges into the load, allowing switch S to turn off under ZCS conditions.
   • The governing equations during this phase are specified.

4. Mode 4: S off, D on

   • The circuit returns to initial condition with the load current maintained through an L-C output filter.

Output Voltage Dynamics

• Energy Balance: Energy from the source equals energy absorbed by the load during a switching cycle:
  • Energy equations relate supplied energy to absorbed energy.
  • Output voltage characteristics indicate dependence on switching frequency and load variations.

Example Parameters for Quasi-Resonant Buck Converter

• Given circuit parameters:
  • Input voltage $V_s = 12 ext{ V}$
  • Inductor L_r = 10 ext{ }0 ext{H}
  • Capacitor C_r = 0.1 ext{ }00F
  • Load current $I_o = 1 ext{ A}$
  • Switching frequency $f_s = 100 kHz$
• Example calculations require deriving peak current and peak voltage from these parameters.

Conclusions

• Soft-switching Techniques: Fundamental principles of implementation and their significance in power electronics.
• Quasi-Resonant Converters: Detailed study on operation modes, waveforms, and output behavior offers insights for advanced converter design.

Resonant Converters

• Topologies include:
  • LC series resonant converter
  • LC parallel resonant converter
  • LLC resonant converter

Additional Techniques

• Zero-switching PWM Circuits: Employ an assistant switch for timing the resonant operation; benefits include improved efficiency and higher device voltage ratings.
• Zero-transition PWM Circuits: Connect resonance in parallel with main switching components; maintains advantages while minimizing device stress.
• Resonant DC-Link Inverters: Integrate resonant circuits into AC-DC-AC conversion systems to enable soft-switching capabilities, optimizing performance and longevity of the system.