LLC Converter Resonance Tracking Under Variable Input Voltage
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Solution Overview
Problem
Existing multi-stage power conversion systems, particularly those using LLC resonant converters, operate inefficiently when the input voltage varies, leading to inefficient operation and reduced battery life, particularly in applications that involve low voltage and high voltage, which is problematic in applications that require high current.
Innovation Solution
Implementing an LLC resonant converter with a switching bridge and resonant tank circuit that adjusts pulse-frequency modulation (PFM) signals to maintain operation at the resonant frequency, using a control circuit to regulate output voltage by varying the modulation index of the sinusoidal pulse-width-modulated (PWM) control signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the LLC resonant converter operates at a fixed switching frequency, then the control scheme is simple, but the system operates inefficiently when input voltage varies outside the resonant frequency range
Solution Approach 1:
The patent implements dynamic frequency adjustment by monitoring the phase difference between voltage and current waveforms and automatically adjusting the switching frequency to maintain resonance. This dynamic adaptation allows the system to operate efficiently across varying input voltage conditions while maintaining a relatively simple control structure based on phase detection.
Solution Approach 2:
The system employs feedback control by continuously monitoring the phase relationship between voltage and current and using this information to adjust the switching frequency. The phase difference serves as the feedback signal that drives the frequency adjustment mechanism, ensuring the converter operates at peak efficiency regardless of input voltage variations.
2Loss of energy
If the switching frequency is adjusted to track resonant frequency, then conversion efficiency is maximized, but the device complexity increases due to additional control mechanisms
Solution Approach 1:
The system performs self-adjustment by automatically detecting phase differences and correcting its own operating frequency without requiring complex external control systems. The converter uses its own operational parameters (voltage and current waveforms) to generate the control signal, eliminating the need for sophisticated external frequency regulation equipment.
Solution Approach 2:
The patent replaces complex mechanical or electronic frequency adjustment mechanisms with a software-based or microcontroller-based phase detection and frequency adjustment system. This substitution reduces hardware complexity while achieving precise frequency tracking through digital or programmable control methods.
3Measurement precision
If PWM control is used for voltage regulation, then voltage control precision is improved, but switching losses increase reducing overall efficiency
Solution Approach 1:
The patent changes the control parameter from duty cycle (PWM) to switching frequency (PFM). By adjusting the frequency rather than the pulse width, the system achieves voltage regulation while operating continuously at or near the resonant frequency, minimizing switching losses. This parameter change allows efficient operation across a wide range of input voltages without the high switching losses inherent in PWM control.
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
Ensures peak efficiency across a wide range of input voltages by maintaining the resonant tank circuit at its resonant frequency, improving efficiency and reducing inefficiencies due to voltage variations.
Implementation Method 1
The LLC resonant converter operates in a resonant mode, where the switching of the power devices (usually MOSFETs or IGBTs) is synchronized with the resonant frequency of the tank circuit. This synchronization minimizes switching losses and improves efficiency.
Data Source
AI summary
According to an embodiment, an LLC resonant converter includes a switching bridge having a plurality of power switches. The switching bridge is configured to receive a DC voltage input and generate a square waveform based on a pulse-modulated frequency (PFM) signal. The LLC resonant converter further includes a resonant tank circuit coupled to the switching bridge. The resonant tank circuit includes a resonant inductor. The resonant tank circuit is excited in response to receiving the square waveform. The PFM signal is adjusted such that the elapsed time between a rising edge of a drain-to-source voltage of a power switch and a zero-crossing point of current flowing through the resonant inductor falls within a predetermined range corresponding to the resonant tank circuit operating at its resonant frequency.