Quasi-Resonant Push-Pull Converter with Dynamic Turns Ratio Control
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Solution Overview
Problem
Conventional push-pull converters face inefficiencies and increased switching losses at higher frequencies and power densities, particularly due to magnetic bias and leakage inductance, which affect the transformer windings and switching devices, leading to reduced efficiency and increased electromagnetic interference.
Innovation Solution
A quasi-resonant push-pull converter is introduced, featuring a transformer with a primary and secondary winding, a resonant circuit, and a switching circuit that modifies the coupling of the rectifier circuit responsive to the DC power source voltage to maintain resonant mode operation across varying input voltages, thereby controlling efficiency and reducing switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If switching frequency is increased to reduce component size and weight, then filter and transformer size are reduced, but switching losses and electromagnetic interference increase
Solution Approach 1:
The patent applies resonant oscillation principles to the switching circuit, using the natural resonant frequency of the circuit components to create a sinusoidal current waveform. This resonant vibration approach allows the circuit to operate at higher frequencies while maintaining low switching losses, as the switching occurs at zero-crossing points of the resonant waveform.
Solution Approach 2:
The patent changes the operating parameters by operating the switching circuit at its resonant frequency rather than at arbitrary high frequencies. By tuning the resonant frequency based on the actual load and source conditions, the system achieves high-frequency operation with minimized switching losses and EMI.
2Speed
If switching frequency is increased to improve filter cut-off frequency, then smaller inductors and capacitors can be used, but inductive turn-off and capacitive turn-on problems are aggravated
Solution Approach 1:
The patent utilizes resonant oscillation to create a sinusoidal current waveform in the switching circuit. This resonant approach ensures that switching transitions occur at zero-crossing points of the current waveform, eliminating inductive turn-off and capacitive turn-on problems while enabling higher filter cut-off frequencies.
3Loss of energy
If soft switching technology is used to reduce switching losses and EMI, then efficiency improves, but circuit complexity increases due to additional resonant elements
Solution Approach 1:
The patent makes the resonant elements serve multiple functions: they enable soft switching to reduce losses, provide frequency tuning capability, and adapt to varying load conditions. The same resonant inductor and capacitor that enable ZVS also facilitate frequency adjustment and load adaptation, reducing the need for separate control mechanisms.
Solution Approach 2:
The resonant circuit automatically adjusts its operating characteristics based on load and source conditions. The resonant frequency and switching timing are self-regulated by the circuit's natural oscillation properties, reducing the need for complex external control circuitry while maintaining soft switching benefits.
4Loss of energy
If resonant mode operation is maintained across varying input voltages, then efficiency is optimized, but control complexity increases to adjust turns ratio
Solution Approach 1:
The patent implements dynamic adjustment of the transformer turns ratio based on input voltage variations. The switching circuit dynamically selects different secondary winding taps to maintain resonant operation across varying input conditions. This dynamic adaptation allows the system to maintain optimized efficiency while responding to changing 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
The quasi-resonant push-pull converter maintains high efficiency and power density by ensuring resonant mode operation over a range of input voltages, minimizing switching losses and electromagnetic interference, and optimizing energy transfer.
Implementation Method 1
A quasi resonant converter operates in resonance only for a part of a switching period. A quasi resonant converter may enable the current or voltage in a switching element to vary quasi-sinusoidally through the resonance of resonant elements with loads.
Implementation Method 2
a transformer having a primary winding and a secondary winding and an input circuit configured to apply a DC power source to the primary winding of the transformer
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention relates to a quasi-resonant push-pull converter and the method for controlling the same, said push-pull converter comprising: a direct current (DC) input power supply configured to supply DC input for the converter; a first power input unit and a second power input unit, connected to said DC input power supply, respectively and configured to supply input for the converter in different periods, comprising a first power switching tube and a second power switching tube, a first primary winding and a second primary winding; a power output circuit, configured to supply output of the converter, comprising secondary windings and full-bridge rectification circuits; a first output capacitor and a second output capacitor connected to said power output circuit and configured to store DC electric energy output by the power output circuit in which a resonant element is arranged to achieve a quasi-resonant switching circuit through voltage feedback; and a switching circuit being controlled through voltage feedback, whereby turns ratio of the primary windings and the secondary windings of the push-pull converter is controlled.