LLC Resonant Converter Frequency Control via Primary Current Slope
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Solution Overview
Problem
Resonant power converters face efficiency issues due to changes in resonant frequency over time caused by manufacturing tolerances, aging, and temperature variations, which existing technologies fail to effectively address.
Innovation Solution
The solution involves controlling the switching frequency of LLC resonant power converters based on the slope of the current waveform of the primary winding, adjusting the on-time of the high-side electrically controlled switch to maintain operation at or near resonance by increasing or decreasing the frequency as necessary, and toggling between resonance and slightly below resonance in steady-state operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the resonant power converter operates at a fixed switching frequency, then the device complexity is reduced, but the efficiency deteriorates due to resonant frequency drift caused by manufacturing tolerances, aging, and temperature variations
Solution Approach 1:
The patent implements feedback control by detecting the current waveform characteristics (specifically the zero-crossing point or valley point) of the resonant circuit and using this information to dynamically adjust the switching frequency. The controller monitors the actual resonant frequency drift and adjusts the switching frequency to track the resonant frequency, thereby maintaining efficient operation despite changes in operating conditions, manufacturing tolerances, or aging effects.
Solution Approach 2:
The patent transitions from a static fixed-frequency switching approach to a dynamic frequency adjustment approach. The switching frequency is no longer fixed but is dynamically adjusted in real-time based on the detected resonant frequency characteristics. This allows the system to adapt to changing conditions and maintain optimal efficiency throughout the device's operational life.
2Loss of energy
If the switching frequency is dynamically adjusted to track resonant frequency, then the efficiency is improved, but the device complexity increases due to additional sensing and control circuitry
Solution Approach 1:
The patent employs self-service by utilizing the existing current waveform in the resonant circuit as the feedback signal. Instead of requiring additional complex sensing circuitry to detect resonant frequency, the system uses the naturally occurring current waveform characteristics (zero-crossing or valley points) that are already present in the resonant circuit operation. This minimizes the additional complexity while achieving efficient frequency tracking.
Solution Approach 2:
The patent makes the existing current sensing circuit serve multiple functions: it both drives the resonant circuit and provides the feedback signal for frequency adjustment. The same current waveform that is necessary for power conversion also contains the information needed for frequency tracking, eliminating the need for separate sensing circuits and reducing overall system complexity.
3Power
If the on-time is extended to compensate for frequency drift, then the power transfer is improved, but the stability deteriorates due to potential operation away from resonance
Solution Approach 1:
The patent uses feedback control to detect when the system operates away from resonance by monitoring current waveform characteristics and automatically adjusts the on-time to bring the operation back to resonance. This closed-loop control ensures that power transfer is optimized while maintaining operational stability, as the system continuously corrects deviations from the resonant operating point.
Solution Approach 2:
The patent implements periodic adjustment of the on-time based on the detected resonant frequency characteristics. By periodically measuring the current waveform and adjusting the on-time in a cyclic manner, the system maintains stable operation at resonance while ensuring optimal power transfer, preventing the system from drifting into unstable operating conditions.
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 ensures efficient operation by maintaining the LLC resonant converter at optimal frequency, enhancing efficiency and stability by dynamically adjusting the switching frequency in response to changes in resonant frequency, thereby improving power transfer and reducing power loss.
Implementation Method 1
Resonant power converters utilize a resonant circuit on the primary side of the power converter to create an alternating current (AC) signal applied to a primary winding of a transformer
Implementation Method 2
Electrically-controlled switches on the primary side of the resonant power converter are used to create the AC signal and are controlled by a primary-side controller
Implementation Method 3
The AC signal applied to the primary winding is transferred across the transformer to create an AC signal on a secondary winding of the transformer
Implementation Method 4
The AC signal on the secondary winding is then rectified to supply a direct current (DC) voltage to a load
Data Source
AI summary
Controlling switching frequency of LLC resonant power converters. At least one example embodiment is a method of operating LLC converter, including: measuring values indicative of current through a primary winding of a transformer of an LLC converter, the measuring during a first on-time of a first switching period of an electrically controlled switch coupled to the primary winding, and the measuring creates a current waveform; calculating a slope of the current waveform; and controlling frequency of switching the electrically controlled switch based on the slope.