Multilevel LLC DC/DC Converter Control for Wide Output Voltage
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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 fail to provide a sufficiently wide range without compromising efficiency or increasing part count.
Innovation Solution
A multi-level topology is employed for the LLC resonant converter, using a serial half-bridge configuration where each switching device blocks only half of the input voltage, combined with a control method that switches between symmetrical and asymmetrical modulation schemes to adjust the output voltage range, allowing for efficient operation at or near the resonant frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional LLC resonant converter operates at wide frequency range to achieve wide output voltage range, then output voltage range is improved, but efficiency deteriorates
Solution Approach 1:
The patent applies dynamics by making the converter operate in two distinct modes (full-bridge and half-bridge) that can be dynamically switched based on the required output voltage. The controller selectively activates different switching devices to change the effective transformer turns ratio, allowing the system to adapt to wide output voltage ranges while maintaining optimal operating conditions in each mode, thereby avoiding the efficiency loss associated with operating far from resonant frequency.
Solution Approach 2:
The patent segments the operating range into two distinct regions: a first output voltage range handled by full-bridge mode and a second output voltage range handled by half-bridge mode. This segmentation allows each mode to be optimized for its specific voltage range, with the full-bridge mode handling higher voltages and the half-bridge mode handling lower voltages, thus maintaining efficiency across the entire wide output range without requiring continuous operation at suboptimal frequencies.
2Adaptability or versatility
If LLC resonant converter uses high input voltage to achieve wide output voltage range, then output voltage range is improved, but device cost and complexity increase
Solution Approach 1:
The patent uses dynamic switching between full-bridge and half-bridge configurations to effectively change the transformer turns ratio. By controlling which switching devices are active, the system can achieve different voltage transformation ratios without physically changing the transformer or using high-voltage components. This dynamic reconfiguration allows wide output voltage range with standard-voltage components, reducing cost and complexity.
Solution Approach 2:
The patent changes the effective transformer turns ratio parameter by selectively enabling different switching devices in the full-bridge or half-bridge configuration. This parameter change allows the same physical transformer to provide different voltage transformation ratios, achieving wide output voltage range without requiring high-voltage rated components or multiple transformers, thereby reducing device cost and complexity.
3Adaptability or versatility
If LLC resonant converter operates away from resonant frequency to achieve wide output voltage range, then output voltage range is improved, but efficiency deteriorates
Solution Approach 1:
The patent dynamically switches between full-bridge and half-bridge modes to maintain optimal operating conditions. In each mode, the controller adjusts the switching frequency to be close to the resonant frequency of the corresponding circuit configuration. This dynamic mode switching allows the system to achieve wide output voltage range while maintaining high efficiency in each operating region, avoiding the need to operate continuously far from resonant frequency.
4Adaptability or versatility
If conventional LLC resonant converter uses fixed circuit parameters to achieve wide output voltage range, then output voltage range is limited, but circuit simplicity is maintained
Solution Approach 1:
The patent employs a dynamic control scheme that selectively switches between full-bridge and half-bridge configurations based on the desired output voltage. The controller monitors the output voltage and automatically transitions between modes to maintain optimal performance across the wide output voltage range. This dynamic control approach achieves extended voltage range capability while using the same physical circuit parameters, with the complexity confined to the control logic rather than the power circuit itself.
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 a wide output voltage range with reduced switching loss and balanced current stress across primary switching devices, improving efficiency and extending the maximum-to-minimum DC gain ratio without increasing the device switching frequency significantly.
Implementation Method 1
a resonant circuit formed by a resonant inductor, a resonant capacitor, and a transformer magnetizing inductance
Data Source
Figure 1A
Figure 1B
Figure 2A
AI summary
An efficient control method for an isolated multilevel DC/DC resonant converter (700, 800, 1000, 1400, 1600, 1650, 1700, 1750, 1800, 2100) 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 (801, 1401, 1601, 1651, 1701, 1751, 1801, 2101) selects one of three different modulation schemes to operate the primary-side switching devices of the resonant converter (700, 800, 1000, 1400, 1600. 1650, 1700, 1750, 1800, 2100) based on at least one of output voltage (Vo), output current (Iο), 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 (Vo).