LLC Resonant Converter Capacitance Changeover for Switch Protection
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Solution Overview
Problem
Conventional LLC resonant converters face issues with switch breakdown due to shoot-through currents or surge voltages and loss of output voltage control when changing the capacitance of the resonant capacitor, particularly during transitions from low-frequency to high-frequency characteristics.
Innovation Solution
The LLC resonant converter incorporates a resonant capacitor changeover circuit with a switch and a second capacitor connected in series, controlled by an input voltage detection circuit, output voltage detection circuit, and output current detection circuit to manage the changeover switch and bridge circuit operations, ensuring stable frequency control and preventing shoot-through currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the capacitance of the resonant capacitor is changed during operation, then the gain and operating frequency can be adjusted to maintain output voltage under varying input conditions, but switch breakdown due to shoot-through currents or surge voltages occurs
Solution Approach 1:
The control method performs preliminary actions by detecting input voltage changes and proactively adjusting the resonant capacitor capacitance before shoot-through currents or surge voltages can occur. The controller monitors the input voltage and preemptively changes the capacitance value to prevent harmful current spikes, thereby maintaining both adaptability and switch reliability.
Solution Approach 2:
The system employs feedback control by continuously detecting the input voltage and the state of the resonant capacitor, then automatically adjusting the capacitance to optimal values. This closed-loop feedback mechanism ensures that capacitance changes occur at the right moment to adapt to input voltage variations while preventing switch breakdown from shoot-through currents.
2Adaptability or versatility
If the resonant capacitor capacitance is adjusted to maintain output voltage, then the converter can operate across a wide input voltage range, but loss of output voltage control occurs during transitions
Solution Approach 1:
The controller performs preliminary detection of input voltage changes and proactively adjusts the resonant capacitor capacitance before the transition occurs. This preliminary action ensures that the capacitance is already optimized when the input voltage changes, preventing loss of output voltage control during transitions while maintaining wide operating range capability.
Solution Approach 2:
The system uses feedback control to continuously monitor both the input voltage and output voltage, automatically adjusting the resonant capacitor capacitance to maintain stable output voltage control. This feedback mechanism ensures that capacitance adjustments are made at the appropriate moments to preserve both adaptability and control reliability.
3Adaptability or versatility
If a resonant capacitor changeover circuit with switch and second capacitor is added, then capacitance can be changed to adapt to input voltage, but device complexity increases
Solution Approach 1:
The resonant capacitor changeover circuit merges the first capacitor and second capacitor into a single resonant capacitor structure that can dynamically adjust its total capacitance. By combining these capacitors with switching capability, the circuit achieves capacitance adjustability for adapting to input voltage changes while minimizing the increase in device complexity through integrated design.
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
This solution prevents switch breakdown and maintains output voltage control, allowing for high-efficiency and high-gain operation, facilitating the downsizing of power units by reducing stress on the bridge circuit switches and minimizing inrush currents during capacitance changes.
Implementation Method 1
This LLC current resonant converter 1 is an isolated DC/DC converter that can reduce a switching loss and noise that occur in the semiconductor devices on the primary side and the secondary side, by utilizing resonance of the single capacitance Cr and the two inductances Lm, Lr.
Data Source
Figure 1
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Figure 3
AI summary
The LLC resonant converter (100) includes a bridge circuit (10) configured to receive a DC input voltage (Vin), an LLC resonant circuit (20) connected to the bridge circuit (10), a transformer (30) connected to the LLC resonant circuit (20), a rectifier circuit (40) connected to the transformer (30) and configured to send out a converted DC voltage, a resonant capacitor changeover circuit (50), a bridge circuit control section (64), and a resonant capacitor changeover control section (65). When the input voltage (Vin) exceeds a changeover voltage, the operating frequency is raised higher than the resonance frequency, and thereafter the switch (Q3) is turned off.