Self-Oscillating LLC Converter Threshold Control
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Solution Overview
Problem
Conventional resonant LLC converters face challenges in achieving efficient power factor correction and stable operation due to high gain ratio requirements and sensitivity to threshold variations, especially when used as AC/DC converters, which complicates feedback control and leads to issues like false triggering and asymmetrical output currents.
Innovation Solution
The implementation of a self-oscillating LLC circuit with a control circuit that uses electrical feedback parameters to generate gate drive signals for the high side and low side switches, employing an outer control loop to set threshold levels based on output voltage or current and rectified input voltage, and an inner control loop to compare these parameters with thresholds, allowing for threshold-based switching control without the need for a balancing controller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional resonant LLC converters are used for AC/DC conversion with power factor correction, then power factor correction can be achieved, but the system becomes sensitive to threshold variations and requires high gain ratio, leading to false triggering and asymmetrical output currents
Solution Approach 1:
The patent extracts the threshold-based control function from the conventional feedback control system. By using the resonant capacitor voltage threshold directly to control the half-bridge switching, the system eliminates the need for complex balancing controllers and current measurement circuits, thereby reducing device complexity while maintaining operational stability.
Solution Approach 2:
The resonant capacitor voltage itself serves as the control parameter. The threshold of the resonant capacitor voltage automatically provides the control signal for the half-bridge switches, making the system self-regulating without requiring external balancing controllers or complex feedback mechanisms.
2Ease of operation
If threshold-based control is used in resonant converters, then control simplicity is improved, but sensitivity to threshold variations increases, causing false triggering
Solution Approach 1:
The patent implements feedback by using the resonant capacitor voltage threshold as the control parameter. The threshold comparator continuously monitors the resonant capacitor voltage and adjusts the switching timing accordingly, providing automatic compensation for threshold variations and preventing false triggering while maintaining control simplicity.
3Manufacturing precision
If conventional feedback control is used in LLC converters, then output regulation can be achieved, but circuit complexity increases due to the need for balancing controllers and input current measurement
Solution Approach 1:
The patent extracts the essential control function from conventional feedback systems by using only the resonant capacitor voltage threshold. This eliminates the need for balancing controllers, input current measurement circuits, and complex feedback loops, thereby reducing circuit complexity while maintaining adequate output regulation through the inherent resonant characteristics.
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 approach enables efficient power factor correction and stable operation by reducing complexity and sensitivity to threshold variations, achieving a high power factor and minimizing total harmonic distortion, while avoiding the need for input current measurement and reducing circuit complexity.
Implementation Method 1
Resonant converters which comprise an LLC resonant circuit having two inductances and one capacitance are well-known. Such converters have the advantage that energy-efficient operation with relatively low switching losses is possible.
Data Source
AI summary
Various improvements are provided to resonant DC/DC and AC/DC converter circuit. The improvements are of particular interest for LLC circuits. Some examples relate to self-oscillating circuit and others relate to converter circuits with frequency control, for example for power factor correction, driven by an oscillator.