Resonant Converter Capacitive Mode Detection and Frequency Control
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Solution Overview
Problem
LLC resonant converters face high switching losses and instability when operating in capacitive mode due to hard switching, which can lead to MOSFET damage and circuit failure under overload conditions.
Innovation Solution
A power supply system with a controller that includes a variable switching circuit and counter logic circuit to detect capacitive mode and increase the resonant converter's frequency, shifting it to inductive mode for zero voltage switching (ZVS) operation, thereby preventing hard switching and ensuring stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the resonant converter operates in capacitive mode under overload conditions, then the operating frequency is minimized, but hard switching occurs causing high switching loss and MOSFET damage
Solution Approach 1:
The controller includes a capacitive mode detector that monitors the resonant converter's operating state and provides feedback signals. When capacitive mode is detected (indicating overload conditions), the detector triggers the frequency adjustment mechanism to increase the operating frequency, thereby preventing hard switching and maintaining ZVS operation
Solution Approach 2:
The system dynamically changes the operating frequency parameter in response to detected capacitive mode conditions. By increasing the frequency from the minimized state back to a higher operating point, the system shifts the resonant converter from capacitive to inductive mode, ensuring soft switching operation and preventing MOSFET damage
2Productivity
If the resonant converter operates in capacitive mode, then the input current passes the voltage, but this causes hard switching and high switching loss
Solution Approach 1:
The capacitive mode detector continuously monitors the relationship between input current and voltage phase. When it detects that current passes voltage (capacitive mode indication), it triggers feedback control to adjust the operating frequency, thereby eliminating hard switching and reducing switching loss
Solution Approach 2:
The system dynamically adjusts the operating frequency based on real-time detection of capacitive mode conditions. This dynamic frequency modulation allows the resonant converter to transition from static capacitive mode operation to dynamic inductive mode operation, maintaining soft switching and reducing energy loss
3Ease of operation
If the resonant converter operates in capacitive mode, then the body diode reversely recovers, but this generates spike current and serious noise
Solution Approach 1:
The capacitive mode detector anticipates the harmful effects of reverse recovery by detecting capacitive mode conditions before they cause damage. By triggering frequency adjustment in advance, the system prevents the body diode from entering reverse recovery state, thereby eliminating spike current and noise generation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents hard switching and maintains ZVS operation even under overload conditions, enhancing switching efficiency and circuit stability by converting the resonant converter to an inductive mode when capacitive mode is detected.
Implementation Method 1
an operating frequency of a waveform is a resonant frequency decided by a resonance between the leakage inductance Lr and the capacitor Cr
Implementation Method 2
when the MOSFET, i.e., switches Q1 and Q2 are turned on, they achieve a zero voltage switching (ZVS). That is, when a voltage of the opposite ends of the MOSFET becomes a zero potential by a current flowing through an internal diode, the switches Q1 and Q2 are turned on
Data Source
AI summary
A resonant converter, a power supply and a power controlling method thereof are provided. The power supply includes a resonant converter which includes a square wave generator configured to alternately turn on and off first and second switches according to a frequency to generate a square wave, a resonant wave generator configured to generate a resonant wave corresponding to the square wave and a rectifier configured to output a voltage corresponding to the resonant wave; and a controller configured to control a frequency modulation of the resonant converter, wherein the controller includes a variable switching circuit configured to increase the frequency of the resonant converter in response to the resonant converter entering a capacitive mode.