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Alternative to inverter filters cuts losses, weight and size

23 October, 2017

A pair of US researchers have developed an alternative to passive filters for inverters which, they say, will cut losses, as well as saving costs, space and weight.

Oleg Wasynczuk, a professor in Purdue University’s School of Electrical and Computer Engineering, and Minyu Cai, a recent PhD graduate from the School, have built a 800W prototype inverter using their technology which, they report, reduced system losses by 20%, compared to a conventional inverter and filter combination.

Inverters usually need passive filters to protect motors from the effects of high voltage edge rates (dv/dt). But these filters increase the inverter’s power losses, weight and size. The Purdue researchers have developed a circuit – which they are calling “auxiliary resonant soft-edge pole”, or Arsep – that controls dv/dt using a soft-switching mechanism which eliminates the need for a filter and reduces power losses.

“High dv/dt can cause over-voltages at motor or inverter terminals, electromagnetic interference, and failure of motor bearings because of micro-arcs. These effects lead to shorter motor life times,” says Cai. “Our technology can reduce the dv/dt at a much lower cost than passive filters.”

Instead of adding passive filters, which conduct continuously, the Arsep circuit augments an inverter with auxiliary circuits that are active only during voltage transitions.

“The auxiliary circuits are only active for short time periods,” Cai explans. “Therefore, the average current going through the circuits are small, which results in lower power losses and smaller components.”

The Arsep technology (a combination of hardware and control software) not only reduces losses compared to passive filters, it can also reduce losses in the main inverter circuit. “Soft-switching eliminates switching losses to almost negligible levels,” Wasynczuk explains. “So you are able to achieve a better efficiency compared to the current state-of-the-art.”

Filter rival: the Arsep power board (driver board not shown)

The researchers built their 800W prototype inverter with the help of about $150,000 of funding from the US Department of Energy, which was part of a larger award. They say that its Arsep circuit was 45% lighter, and occupied 61% less volume than would have been needed for a passive filter.

“That is a significant improvement,” Wasynczuk says. “Now we want to show it’s commercially viable.”

The Purdue researchers believe that their technology has many potential applications. For example, it could result in smaller, more efficient drive systems for hybrid and electric cars, trucks, and other forms of transport. The developers are hoping that automotive manufacturers, train-, ship- and aircraft-builders, and manufacturers from other industries, such as heating, ventilation and air conditioning, and renewable energy, will be interested in working with them to develop the technology further.

The Arsep system can be used with either DC-DC or AC-DC converters. Although the technology can be retrofitted to existing inverters, Wasynczuk says that it would be better to integrate it with the inverter circuitry during production.

Wasynczuk and Cai have filed for a provisional patent for their circuitry through Purdue’s Office of Technology Commercialization.

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