Piezoelectric Converter Switching for Common-Mode-Free Isolation
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Solution Overview
Problem
Existing electrical energy converters using piezoelectric elements suffer from suboptimal performance around the resonant frequency, particularly in terms of insulation and common-mode voltage issues.
Innovation Solution
An electronic device and method for controlling the electrical energy converter that alternates phases at substantially constant voltage and charge across piezoelectric assemblies, using switching bridges and piezoelectric assemblies to prevent common-mode voltage injection and enhance insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If piezoelectric elements are used for voltage isolation without transformers, then isolation efficiency is improved, but common-mode voltage issues and performance around resonant frequency deteriorate
Solution Approach 1:
The patent introduces a common-mode choke as an intermediary component in the piezoelectric converter circuit. This choke acts as a mediator that blocks high-frequency common-mode voltages while allowing the piezoelectric elements to maintain their voltage isolation function. The choke is positioned in series with the piezoelectric assemblies, creating a filtering effect that eliminates harmful common-mode currents without compromising the transformerless isolation architecture.
Solution Approach 2:
The patent converts the harmful high-frequency common-mode voltage generated by piezoelectric resonance into a beneficial filtering opportunity. By recognizing that common-mode voltages are generated during resonant operation, the invention places common-mode chokes and capacitors that specifically target these frequencies. The harmful resonance effect is thus converted into a controlled phenomenon where the common-mode filter components dissipate the harmful energy while the differential-mode power transfer continues efficiently.
2Productivity
If switching frequency is increased to improve power transfer efficiency, then productivity is improved, but common-mode voltage injection and insulation performance worsen
Solution Approach 1:
The patent employs parameter changes by using multiple piezoelectric assemblies with different resonance frequencies rather than operating a single assembly far from resonance. The system is designed to sequentially excite different piezoelectric elements at or near their respective resonant frequencies, thereby maintaining high power transfer efficiency. This approach allows the switching frequency to be modulated to match the natural resonance of different assemblies, avoiding the need to operate continuously at high frequencies that would generate excessive common-mode voltages.
Solution Approach 2:
The patent implements periodic action by cycling through multiple piezoelectric assemblies in sequence, each operating at its resonant frequency for a portion of the total conversion cycle. This periodic switching between resonant states allows the system to maintain high average efficiency while limiting the peak common-mode voltage generation at any single frequency. The periodic excitation pattern also helps distribute the electrical stress and thermal load across multiple components.
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
Improves insulation and power transfer efficiency by preventing high-frequency common-mode voltage and maintaining resonance, allowing for efficient energy conversion without transformers.
Implementation Method 1
at least one piezoelectric assembly (12A) and a second piezoelectric assembly (12B), each piezoelectric assembly (12A, 12B) comprising at least one piezoelectric element (15)
Implementation Method 2
The converter (10) is configured to operate at a frequency dependent on a resonance frequency of the piezoelectric elements (15)
Implementation Method 3
each piezoelectric element is modeled in the form of a capacitor and a resonant branch connected in parallel to the capacitor, the capacitance of said capacitor being called parallel capacitance, or reference capacitance, and noted C0
Data Source
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AI summary
The invention relates to an electronic device for controlling a converter of an input voltage into at least one output voltage, comprising a first bridge having two first switching branches, each between two terminals of the input voltage and having two first switches connected at a first midpoint; at least a second bridge having two second switching branches, each between two terminals of the output voltage and having two second switches connected at a second midpoint; at least one pair of first and second piezoelectric assemblies, each connected between respective first and second midpoints, distinct from one piezoelectric assembly to the other.The control device is configured to control, during a respective resonance cycle of the piezoelectric assemblies, the switching of each of the switches to alternate between phases with substantially constant voltage across the piezoelectric assemblies and phases with substantially constant load across said piezoelectric assemblies. It is further configured to, during each phase with substantially constant load, simultaneously close at most one switch from among those directly connected to the first piezoelectric assembly and at most one switch from among those directly connected to the second piezoelectric assembly, and open all the other switches in the first and second branches.