Isolated LLC DC/DC Converter Control for Wide Output Voltage Range
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Solution Overview
Problem
Conventional LLC resonant converters face challenges in achieving a wide output voltage range while maintaining efficiency, as they often require high input voltages, leading to increased costs and complexity, and existing solutions do not adequately support voltage ranges beyond 200 volts to 1000 volts in electric vehicle charging applications.
Innovation Solution
A serial half-bridge LLC resonant converter with a control method that selects between symmetrical, asymmetrical, and three-level modulation schemes based on output voltage and current conditions, allowing for a narrow device switching frequency range and efficient operation across a wide output voltage range, while also adjusting circuit parameters to achieve desired DC voltage gains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the LLC resonant converter operates at a very wide frequency range to achieve wide output voltage range, then the output voltage range is improved, but the efficiency deteriorates
Solution Approach 1:
The patent applies dynamics by making the converter operate in two distinct modes (first mode with lower frequency for high voltage gain, second mode with higher frequency for low voltage gain) that can be dynamically switched based on operating conditions. This dynamic mode switching allows the system to maintain high efficiency in each mode while achieving wide overall voltage range coverage.
Solution Approach 2:
The patent segments the operating range into two distinct frequency ranges (first frequency range for high voltage gain, second frequency range for low voltage gain). By dividing the continuous frequency range into discrete segments with different characteristics, the system can optimize efficiency in each segment while collectively covering a wide output voltage range.
2Adaptability or versatility
If the LLC resonant converter uses fixed circuit parameters to achieve wide output voltage range, then the output voltage range is improved, but the efficiency deteriorates
Solution Approach 1:
The patent introduces dynamic control by switching between two operating modes with different frequency ranges based on the desired output voltage. This dynamic adaptation allows the system to maintain optimal efficiency points in each mode while achieving wide overall voltage regulation range, overcoming the limitation of fixed parameter designs.
3Adaptability or versatility
If high input voltage is used to achieve wide output voltage range, then the output voltage range is improved, but the device complexity and cost increase
Solution Approach 1:
The patent changes the operating frequency parameter dynamically between two modes to achieve wide output voltage range without requiring high input voltage. By varying the switching frequency between a first frequency range (for high voltage gain) and a second frequency range (for low voltage gain), the system achieves flexible voltage regulation with standard input voltage levels, reducing the need for high-voltage components.
4Power
If the switching frequency is reduced to achieve high voltage gain, then the DC voltage gain is improved, but the efficiency deteriorates
Solution Approach 1:
The patent applies dynamics by implementing two distinct operating modes: a first mode with lower switching frequency that provides high DC voltage gain, and a second mode with higher switching frequency that provides low DC voltage gain. The system dynamically switches between these modes based on the required output voltage, allowing high voltage gain to be achieved only when necessary while maintaining high efficiency in normal operating conditions.
Solution Approach 2:
The patent segments the voltage gain requirement into two ranges handled by different frequency modes. The first frequency range handles high voltage gain requirements, while the second frequency range handles low voltage gain requirements. This segmentation allows each mode to operate in its optimal efficiency region while collectively providing the full range of voltage regulation.
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 solution enables efficient regulation of output voltage over a wide range (0.125Vin to 0.8Vin) with reduced device switching frequency, improved efficiency, and flexibility in circuit parameters, supporting both fixed and variable input voltages, and various secondary-side topologies.
Implementation Method 1
an isolation transformer having first and second windings, wherein the first winding is connected between third and fourth electrical nodes in the LC resonant circuit
Implementation Method 2
an LC resonant circuit connected between a first electrical node in the first pair of the switching devices and a second electrical node in the second pair of switching devices
Implementation Method 3
an LC resonant circuit connected between a first electrical node in the first pair of the switching devices and a second electrical node in the second pair of switching devices
Data Source
AI summary
An efficient control method for an isolated multilevel DC/DC resonant converter achieves a wide output voltage range with a narrow device switching frequency range, relative to the output voltage range and the device switching frequency range of the prior art. At any given time, a control circuit selects one of three different modulation schemes to operate the primary-side switching devices of the resonant converter based on at least one of output voltage, output current, input signal, and one or more external control signals. Together with a selected device switching frequency, the three modulation schemes generate different voltage waveforms to a primary-side transformer, which are coupled to the secondary-side to provide different output voltages.