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Soft-switching boosts drive efficiencies and cuts size and costs

01 June, 2018

A Californian company has developed a technology which, it claims, effectively eliminates transistor switching losses in hard-switched architectures for almost any power converter topology. Pre-Switch says that its soft-switching technology will dramatically reduce the cost, size and weight of converters used in motor drive, renewable energy, electric vehicle, traction and server applications, while increasing efficiency and reliability. The reduction in switching losses is claimed to be 70–90% for any type of solid-state switch and any converter topology.

Pre-Switch predicts that its technology could significantly reduce the 20% of the world’s electrical energy currently estimated to be lost in power conversion technologies that have not changed much for 30 years.

Potential users, including the Brazilian drives-maker, WEG, are already assessing the technology.

Using embedded AI (artificial intelligence) controller chips, the Pre-Switch technology learns and adapts its performance on a cycle-by-cycle basis, to achieve resonant soft-switching across changing loads, input voltages, temperatures and manufacturing tolerances. The technology is claimed to have demonstrated efficiencies that are higher than those of five-level topologies at a fraction of the cost and complexity.

The technology also lowers EMI (electromagnetic interference) “significantly” and reduces dV/dt for any type of switch. It allows low-cost IGBTs to achieve “silicon-carbide-like” performance, and allows SiC- and GaN-based topologies to switch up to 20 times faster than they do today. Built into the architecture are cycle-by-cycle safety functions and communications that were not previously possible.

Pre-Switch reports that it has switched 900V Wolfspeed SiC Mosfets at up to 1MHz, and 650V Infineon IGBTs at more than 100kHz, with “unprecedented” efficiencies. It adds that the technology can presently be applied to applications ranging in size from 1kW to “above gigawatts”.

“We have removed the biggest barrier to advancing the power conversion industry,” says Pre-Switch CEO, Bruce Renouard. “Our technology enables simple, reliable and cost-effective forced resonant soft-switching on any topology.”

Pre-Switch is already working with potential development partners interested in using the new technology in their next generation of power converters. One of these is WEG, the Brazilian manufacturer of variable-speed motor drives.

“By significantly reducing IGBT switching losses without increasing dV/dt, Pre-Switch is creating a possibility to redefine our VFD (variable-frequency drive) motor drives to be smaller and more efficient, without being harmful to motor insulation and bearings,” says WEG’s drives r&d manager, Adalberto Jose Rossa. “We are investigating this technology, and initial test results at double-pulse and at short-circuit conditions have inspired us to test a complete drive with Pre-Switch technology. We look forward to analysing reliability data of the system under real motor load conditions.”

A power converter circuit showing the additional components needed for the Pre-Switch technology in green

“The higher switching frequencies enabled by Pre-Switch are able to provide a lower motor current ripple,” adds Rossa’s colleague, Carlos Afonso Hümmelgen, who is WEG’s drives r&d coordinator. “Lower motor current ripple yields reduced motor harmonic losses, and increased motor and system efficiency.”

Pre-Switch, located at Los Gatos in Silicon Valley, was founded by experts in power semiconductors, power systems, robotics, and artificial intelligence. It emerged from an attempt to eliminate distortion-causing losses in Class-D audio amplifiers. The technology was presented to industry leaders in the power semiconductor market who couldn’t classify it in  their existing product portfolios. But the idea of a world without switching losses was too big to ignore, so the team regrouped, secured investors and brought in further experts.

Pre-Switch envisages a world in which everything using fossil fuel today will be electrically driven and controlled – a world in which power converters that are a fraction the cost, size and weight of today’s motor drives, save massive amounts of power currently wasted in industrial applications. They also foresee their technology shrinking electric motors and driving the efficiency required for further electrical innovation in transportation. They even predict a future of energy-independent, solar-powered homes, free of utility bills and power line connections.

The Pre-Switch technology will make its public debut at the PCIM Europe 2018 exhibition and conference in Germany, from 5–7 June.

There are patents pending globally on the technology.

Pre-Switch says its technology can eliminate 80% of an IGBT’s switching losses, while switching five times faster. It can also eliminate 95% of a silicon carbide Mosfet’s switching losses and switch these devices at 1MHz with high efficiencies

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