LLC PFC Pre-regulator Feedback Modulation for THD Reduction
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Solution Overview
Problem
Existing power converter designs face challenges in achieving high efficiency and low total harmonic distortion while handling wide AC input voltage ranges, particularly at light load conditions, due to compromises in size and efficiency, and often require input current sensing which increases losses and circuit complexity.
Innovation Solution
The proposed AC/DC PFC converter employs a resonant LLC PFC pre-regulator with a feedback system that modulates the output voltage based on output power and input voltage characteristics, eliminating the need for input current measurement by using electrical parameters from the LLC circuit, such as capacitor voltage, to control the switching of the half-bridge inverter and achieve a virtually resistive input impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If input current sensing is used to control the PFC pre-regulator, then power factor correction can be achieved, but losses and circuit complexity increase
Solution Approach 1:
The patent extracts the input current sensing function from the control system by using the resonant capacitor voltage as a substitute measurement. Instead of directly sensing the input current, the system measures the voltage across the resonant capacitor in the LLC circuit, which correlates with the input current waveform. This eliminates the need for separate current sensors and reduces both circuit complexity and associated losses.
Solution Approach 2:
The resonant capacitor voltage serves as an intermediary parameter that mediates between the input current and the control system. By measuring this intermediate voltage parameter rather than the input current directly, the system achieves indirect current sensing without requiring additional sensing circuitry, thereby reducing complexity and losses while maintaining PFC functionality.
2Ease of manufacture
If a dual stage system with dedicated PFC pre-regulator is used, then power factor correction is improved, but device complexity increases
Solution Approach 1:
The patent merges the PFC pre-regulator functionality with the LLC resonant converter by integrating the control of both stages through a unified feedback mechanism. The resonant capacitor voltage from the LLC circuit is used to control the PFC pre-regulator, combining what would traditionally be separate control systems into one integrated approach, thereby reducing device complexity while maintaining effective power factor correction.
Solution Approach 2:
The resonant capacitor voltage measurement serves multiple functions: it characterizes the LLC circuit operation and simultaneously provides the control signal for the PFC pre-regulator. This multi-functional use of a single measurement parameter reduces the need for separate sensing and control circuits, simplifying the overall device while maintaining both PFC capability and LLC resonance control.
3Adaptability or versatility
If resonant LLC converter is used for wide AC input voltage range, then adaptability is improved, but efficiency at light load deteriorates
Solution Approach 1:
The patent implements dynamic control of the PFC pre-regulator by modulating the controlled output voltage based on real-time feedback from the resonant capacitor voltage. This dynamic adjustment allows the system to optimize its operating point across varying load conditions and input voltages, maintaining high efficiency at light load while preserving the wide input voltage range adaptability provided by the resonant LLC topology.
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 reduces total harmonic distortion and improves efficiency by controlling the gate switching in the PFC pre-regulator, allowing for a simpler and more modular power converter design that maintains high power factor correction without the need for input current sensing, thus minimizing losses and extra circuitry.
Implementation Method 1
resonant converters which comprise an LLC series-parallel resonant circuit having two inductances and one capacitance
Implementation Method 2
a rectifier for rectifying a mains voltage
Data Source
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AI summary
An AC/DC PFC converter comprises an LLC PFC pre-regulator and a DC/DC converter output stage. The output stage has a feedback unit adapted to provide a feedback signal (in addition to the conventional feedback of the bus voltage error) to the control circuit of the PFC pre-regulator for modulating the controlled output voltage of the PFC pre-regulator in dependence on the output power and/or the input current and voltage. In this way, the total harmonic distortion of the input of the converter can be reduced by controlling the gate switching in the PFC pre-regulator.