Hybrid-Transformer Step-Down Converter with Resonant Switching
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Solution Overview
Problem
Conventional buck converters face challenges in achieving large step-down conversion ratios, such as 12:1 or 24:1, with low efficiency and increased magnetic size due to high turn-off losses and inductive energy storage issues, particularly at high switching frequencies.
Innovation Solution
The introduction of a hybrid-switching method using a resonant inductor and capacitor forming a resonant circuit with a hybrid transformer, which operates as both an inductive and capacitive energy transfer device, allowing for simultaneous inductive and capacitive energy storage and transfer, thereby increasing current to the load and reducing magnetic size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional buck converter topology is used to achieve large step-down conversion ratios, then voltage conversion capability is improved, but efficiency deteriorates due to high turn-off losses
Solution Approach 1:
The patent employs periodic resonant action by introducing a resonant inductor and resonant capacitor that form a resonant circuit. The resonant inductor current oscillates periodically, allowing energy to be transferred to the load during specific intervals of the resonant cycle. This periodic resonant action enables large step-down conversion ratios while reducing turn-off losses because the main switch operates in zero-current switching (ZCS) conditions during the resonant intervals.
Solution Approach 2:
The patent changes the operating parameters by introducing resonant frequency into the switching converter. By operating the converter in a resonant mode where the switching frequency is related to the resonant frequency of the Lr-Cr circuit, the converter achieves improved efficiency. The parameter change from conventional PWM switching to resonant switching allows the converter to maintain low losses while achieving large voltage conversion ratios.
2Power
If conventional buck converter is used for large step-down ratios, then voltage conversion is improved, but magnetic size increases due to inductive energy storage requirements
Solution Approach 1:
The patent utilizes the phase transition of energy storage from purely inductive to a combination of inductive and capacitive. By introducing a resonant capacitor Cr in parallel with the load, the converter transitions between inductive energy storage (in Lr) and capacitive energy storage (in Cr). This phase transition between energy storage modes reduces the burden on the magnetic inductor, allowing for smaller magnetic components while achieving large voltage conversion ratios.
Solution Approach 2:
The resonant capacitor Cr acts as an intermediary energy storage element between the resonant inductor Lr and the load. Instead of requiring the inductor to store all the energy for large step-down ratios, the capacitor serves as a mediator that stores energy during certain intervals and releases it during others. This intermediary capacitive energy storage reduces the required inductance value, thereby reducing magnetic size.
3Loss of energy
If resonant inductor is introduced to improve efficiency, then energy loss is reduced, but circuit complexity increases
Solution Approach 1:
The resonant inductor Lr serves multiple functions simultaneously: it limits the rate of rise of current (di/dt) during the ON interval, stores energy during the resonant interval, and provides a path for zero-current switching. The resonant capacitor Cr also performs multiple functions: it stores energy, provides resonant action, and enables soft switching. This multi-functionality reduces the need for additional components that would otherwise be required to achieve the same effects, thereby limiting the increase in circuit complexity.
Solution Approach 2:
The patent merges the functions of current limiting, energy storage, and soft switching into the resonant inductor Lr and resonant capacitor Cr. Instead of having separate components for each function, the resonant circuit elements combine multiple functions into a single integrated approach. For example, the resonant inductor simultaneously limits di/dt and stores energy for transfer to the load, reducing the overall component count and circuit complexity.
4Speed
If switching frequency is increased to improve transient response, then response speed is improved, but turn-off losses increase
Solution Approach 1:
The resonant circuit creates periodic intervals of zero current through the main switch by utilizing the natural oscillation of the Lr-Cr circuit. During these zero-current intervals, the switch can be turned on or off without incurring turn-off losses. This periodic resonant action allows the converter to operate at high switching frequencies for fast transient response while maintaining low turn-off losses because the switch always operates under zero-current conditions.
Solution Approach 2:
The patent replaces the conventional PWM switching mechanism with resonant switching. Instead of relying on forced commutation or complex gate drive timing to achieve soft switching, the converter uses the natural resonant oscillation of the Lr-Cr circuit to create zero-current switching conditions. This substitution of mechanical/electronic control with natural resonant physics enables high-frequency operation with minimal turn-off losses.
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 enhances efficiency, reduces magnetic size, and allows for fast transient response by providing a continuous discharge path for resonant inductor energy, eliminating leakage inductance losses and achieving higher step-down conversion ratios with reduced voltage stresses on switches.
Implementation Method 1
a resonant inductor and a resonant capacitor forming a resonant circuit for a part of a switching period
Implementation Method 2
The resonant inductor is connected to the primary of the hybrid transformer... Simultaneous inductive and capacitive energy storage and transfer
Implementation Method 3
The resonant inductor is connected to the primary of the hybrid transformer... Simultaneous inductive and capacitive energy storage and transfer
Data Source
AI summary
The present invention employs a resonant inductor, a resonant capacitor and a hybrid transformer using a Hybrid-switching method with three switches which results in two distinct switched-networks: one for ON-time interval and another for OFF-time interval. Resonant inductor is placed in series with the hybrid transformer primary to insure the continuity of primary and secondary currents at the switching transitions and thus eliminating completely the potential switching losses at the switching transitions. In the best use of the invention the resonant inductor is replaced by use of the inherent leakage inductance of the transformer and for the first time eliminate the switching losses always associated with the transformer leakage inductance of all other switching converters. The output voltage is controlled by the standard Pulse Width Modulated (PWM) duty ratio control.