LLC Resonant Converter Control Near the ZVS Capacitive Boundary
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Solution Overview
Problem
Conventional half-bridge LLC resonant converters face challenges in maintaining zero voltage switching (ZVS) due to the risk of entering a capacitive mode, especially under abnormal conditions like output short circuits and overloads, where frequency limiting methods fail, leading to shoot-through currents.
Innovation Solution
A resonant conversion system with a controller that detects changes in the bridge arm midpoint voltage to adaptively adjust current thresholds and perform capacitive protection, ensuring continuous operation in the inductive mode while allowing operation close to the capacitive mode to maximize gain region usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency limiting method is used to maintain inductive mode, then zero voltage switching is ensured, but the system cannot operate close to capacitive mode to maximize gain region
Solution Approach 1:
The patent implements dynamic adjustment of current thresholds based on real-time detection of bridge arm midpoint voltage changes. The controller adaptively modifies the current threshold values during operation, allowing the system to operate close to the capacitive mode boundary while maintaining inductive mode stability. This dynamic approach enables the system to maximize gain region usage without sacrificing zero voltage switching reliability.
2Productivity
If the system operates close to capacitive mode to maximize gain region, then efficiency is improved, but the risk of entering capacitive mode and generating shoot-through current increases
Solution Approach 1:
The patent employs preliminary protective action by detecting changes in bridge arm midpoint voltage before the system actually enters capacitive mode. The controller monitors the voltage changes and preemptively adjusts current thresholds to prevent entry into the dangerous capacitive region. This preliminary detection and protection mechanism allows the system to operate close to the boundary without actually entering it, thereby maximizing efficiency while preventing shoot-through currents.
3Reliability
If conventional frequency limiting is applied, then capacitive mode is avoided, but the system fails under abnormal conditions like output short circuit and overload
Solution Approach 1:
The patent implements a feedback mechanism that continuously monitors bridge arm midpoint voltage changes and uses this information to dynamically adjust current thresholds. Unlike conventional fixed frequency limiting, this feedback-based approach adapts to abnormal conditions such as output short circuits and overloads. The real-time detection and adjustment enable the system to maintain capacitive mode avoidance while properly handling abnormal operating conditions through adaptive threshold modification.
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 system effectively maintains zero voltage switching and maximizes the use of the gain region by continuously operating in the inductive mode, preventing shoot-through currents and optimizing performance under various conditions.
Implementation Method 1
A resonant-type soft switching topology enables soft switching control by using a zero voltage switching (zero voltage switching, ZVS) technology
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3(a)~3(c)
AI summary
This application provides a resonant conversion system, including a controller and a resonant conversion circuit. The resonant conversion circuit includes a high frequency chopper circuit, a resonant cavity, a transformer, and a rectification filter network, and the high frequency chopper circuit includes switches S1 and S2. The controller is configured to: detect a bridge arm midpoint voltage Vsw, and determine a first electrical signal based on the Vsw; determine, based on the first electrical signal, a current threshold signal used to indicate a current threshold; detect a resonant current on a primary side of the transformer, and compare the resonant current with the current threshold signal to determine a second electrical signal that is used to indicate a comparison result; and control on/off of the switch S1 or S2 based on the second electrical signal, so that the system operates in an inductive mode to ensure zero voltage switching of the switch, while operating in a state close to a capacitive mode to maximize the use of a gain region.