Open and closed loop of LLC converter

An LLC resonant converter uses a resonant tank (Lr, Cr, and magnetizing inductance Lm) to achieve soft-switching (ZVS/ZCS).

Open-Loop LLC Converter in Simulink

Circuit Elements:

• Input Voltage Source (DC)
• Full-Bridge or Half-Bridge Inverter (IGBTs/MOSFETs + Gate signals)
• Resonant Tank: Series Lr-Cr and parallel Lm
• High-Frequency Transformer (optional for isolation)
• Rectifier + Filter at Output (typically full-wave)
• Load: Resistive or Constant Power Load

Control:

• In open-loop, the switching frequency is fixed.
• Use a Pulse Generator or SPWM block to drive MOSFETs/IGBTs.

Closed-Loop LLC Converter in Simulink

Feedback Control:

• Use output voltage measurement
• Compare with a reference voltage VrefV_{\text{ref}}Vref​
• Pass error to a PI or PID Controller
• Controller adjusts the switching frequency to regulate the output

Dynamic Control:

• Replace the fixed pulse generator with a Variable Frequency PWM Generator
• The frequency is varied according to the PI output (common in LLC)
• You can use a look-up table or VCO-like behavior to convert control voltage to switching frequency

Output Observation:

• Scope to view:
• Output voltage
• Switching frequency
• Control error
• Inductor current (for ZVS observation)