Researchers develop high-efficiency DC power converter

Researchers at Kobe University have developed a direct current voltage boost converter that reportedly achieves a higher efficiency at lower cost and maintenance than before. The electrical power converter could contribute to the development of electric and electronic components across power generation, health care, mobility and information technology.

Devices that harvest energy from sunlight or vibrations, or power medical devices or hydrogen-fuelled cars, have a key component in common. This “boost converter” converts low-voltage direct current input into high-voltage direct current output. Because it is such a ubiquitous component, it is important that it uses as few parts as possible for reduced maintenance and cost and that it also operates at the highest possible efficiency without generating electromagnetic noise or heat. The main working principle of boost converters is to quickly change between two states in a circuit, one that stores energy and another that releases it. The faster the switching is, the smaller the components can be and therefore the whole device can be downsized. However, this can increase the electromagnetic noise and heat production, which deteriorates the performance of the power converter.

The researchers, led by researcher Mishima Tomokazu, developed the direct current power conversion circuit by combining high-frequency switching (about 10 times higher than before) with a technique that reduces electromagnetic noise and power losses due to heat dissipation, called “soft switching”, while also reducing the number of components.

“When the circuit changes between two states, there is a brief period when the switch is not completely closed, and at that point there is both a voltage and a current across the switch. This means that during this time the switch acts like a resistor and thus dissipates heat. The more often a switch state changes, the more this dissipation occurs. Soft switching is a technique that guarantees that the switch transitions happen at zero voltage, thus minimising the heat loss,” Tomokazu said. Traditionally, this has been achieved by “snubbers”, components that offer alternative energy sinks during the transition period, which subsequently leads to energy losses.

The researchers used “resonant tank” circuits that can store energy during the switching period and therefore have lower losses. They also used a component-saving design with flat components printed onto a circuit board, called a “planar transformer”, which is compact with good efficiency and thermal performance. Tomokazu and his colleagues also built a prototype of the circuit and measured its performance.

“We confirmed that our snubberless design has much reduced electromagnetic noise and a high energy efficiency of up to 91.3%, which is unprecedented for a MHz drive with high voltage conversion ratio. This ratio is also more than 1.5 times higher than existing designs,” Tomokazu said.

The researchers want to further increase the efficiency by reducing the power dissipation of the magnetic components used. “The current development is a 100 W-class small-capacity prototype, but we aim to expand the power capacity to a larger kW-class capacity in the future by improving the electronic circuit board and other components,” Tomokazu said.

The development of a direct current voltage boost converter could be of great relevance to applications in electric power, renewable energy, transportation, information and telecommunications and medical care. The research findings were published in the journal IEEE Transactions on Power Electronics.

Image credit: iStock.com/Fahroni