A high-boost and high-efficiency DC power converter
Kobe team combines fast switching with reduced noise and power losses from heat dissipation
Devices that harvest energy from sunlight or vibrations, or power medical devices or hydrogen-fuelled cars have one key component in common: the 'boost converter' that converts low-voltage direct current input into high-voltage direct current output.
Boost converters quickly change between two states in a circuit, one that stores energy and another that releases it. The faster the switching, the smaller the components. However, this also increases the electromagnetic noise and heat production, which deteriorate the performance of the power converter.
A team of Kobe University power electronics led by researcher Mishima Tomokazu has now made significant progress in developing a new DC power conversion circuit. They've managed to combine high-frequency switching (about ten 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 minimizing the heat loss,” explains Mishima.
Traditionally, this has been achieved by 'snubbers' that offer alternative energy sinks during the transition period, which subsequently leads to energy losses.
The Kobe University team presented their new circuit design and its evaluation in the journal IEEE Transactions on Power Electronics. The key to their achievement is the use of 'resonant tank' circuits that can store energy during the switching period and therefore have much lower losses.
In addition, they use a component-saving design with flat components printed onto a circuit board, called a planar transformer, which is very compact and has both good efficiency and thermal performance.
Mishima 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 percent, 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.”
However, they want to further increase the efficiency by reducing the power dissipation of the magnetic components used.
Mishima explains their plans going forward, saying “The current development is a 100W-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.”
