DC-DC converter boosts piezoelectric power
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Researchers in France have developed a technique that opens up the use of piezoelectric converters in TVs, phones, tablets and electrical tools.
The researchers at CEA-Leti in France have developed a DC-DC converter to reduce the piezoelectric voltage swing and then the circulating current. This one is applied to an isolated dual bridge dc-dc converter based on two piezoelectric resonators (PR).
The principle is validated experimentally, showing improved efficiency of up to 11% and 5% on average to use mechanical motion to produce power. For a 200 V to 120 V conversion, the converter shows an efficiency of 96.2 percent with the inductive assisting circuit, 94.3 percent with the piezoelectric one and 87.4 percent without any assisting circuit. The piezoelectric resonator offers a gain in efficiency over a smaller operating range than the inductance, but leads to a flatter converter.
“For many people, piezoelectricity is associated with energy harvesting and the idea of low power,” researcher Ghislain Despesse. “But in power conversion, piezoelectrics operate at high frequencies, greater than 100kHz, with no limits in terms of input power. That makes it possible to reach power levels of several hundred watts. The range of applications is therefore very broad, with most converters having a rated power of less than 100W.”
One limitation of piezoelectric converters is the parallel capacitance in the equivalent circuit of the resonator. This one needs to be charged and discharged, inducing a circulating current, which induces losses.
The DC-DC converter paves the way to using piezoelectric converters without transformers so that they can be used in a wider range of applications.
The dual-bridge isolated piezoelectric resonator converter (DB-IPRC) provides isolation using two independent piezoelectric resonators. The improved version of the DC-DC converter significantly improves efficiency, while maintaining the converter isolation principle.
The use of piezoelectric resonators instead of inductors in power conversion “will lead to a dramatic reduction in the size of power converters,” said Despesse. “Our results make it possible to extend this type of compact conversion to isolated converters. So this type of converter is now compatible with a much wider range of applications, such as TVs, phones, tablets and electrical tools.”
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