200kW SiC inverter hits 99 percent efficiency

April 20, 2021 // By Nick Flaherty
200kW SiC inverter hits 99 percent efficiency
Pre-Switch has developed a 100kHz, 200kW inverter using three 35mΩ SiC MOSFETs with an efficiency over 99 percent

US startup Pre-Switch has developed a reference design for a 200kW three phase inverter with efficiency over 99 percent using the AI-based switching technology and low cost silicon carbide (SiC) devices.

The CleanWave200 evaluation inverter exceeds 99.3% at 100kHz using only three discrete, low cost 35 mΩ SiC MOSFETs from UnitedSiC per switch location. This is achieved using a machine learning algorithm to constantly predict the zero voltage switching point. This both reduces the switching losses, increasing the efficiency, and significantly reduces the cost of the SiC MOSFETs required.

The Pre-Switch controller analyzes multiple inputs on a cycle-by-cycle basis, making adjustments in real time to small, forced-resonant transistors enabling perfect soft-switching in harsh changing environments. Variations in system temperature, device degradation, changing input voltages and abrupt current swings are all accounted for and optimized within the Pre-Switch AI algorithm.

“We time the current and charge up the capacitors for nanoseconds, around 100ns, at the zero voltage, zero current point,” Bruce Renouard, CEO of Pre-Switch told eeNews Power. “We achieve the timing to 2ns of precision and adjust every cycle, that’s the beauty of the scheme. You can do this for certain points in power but it’s the changing conditions in infinite variety that creates the problem, and that’s why we use AI. We have a patent on predicting the timing.”

“The reason we use AI is we are taking a lot of data that’s incomplete in a noisy environment and calculate where the switching will be,” he said. “We monitor the device temperature, device switching speeds, and we measure how it reacts and degrades over time so we change the algorithm to compensate that. We do some pattern matching but we are not using a lookup table, we calculate the individual responses for each individual transistor on a cycle by cycle basis.”

Pre-Switch has published data on the system efficiency for 50-100 kHz switching speeds, input voltages, power output and current output, enabling system designers to compare the Pre-Switch results for designs such as electric vehicles.

“We are shipping the CleanWave200 evaluation systems to initial customers around the world, and the efficiency data we are making public today more than justifies our design goals,” said Renouard. “Customers could use the Pre-Switch technology with even better MOSFETs and expect to get incremental performance gains, but there is no other approach that even comes close to 99.3% efficiency at 100kHz with such few, low cost SIC MOSFETs.”

“Switching losses using our Pre-Switch technology are effectively zero,” said Renouard. “If we put that into perspective, an EV with Pre-Switch technology improves inverter efficiencies, producing a pure sine wave output that dramatically improves motor efficiency at low torques where people drive. This will result in an increase its range by up to 12%.”

The Cleanwave200 evaluation system, reference design and design files can be ordered from Pre-Switch. The company has a strategic deal with Foxy Power in Germany and has shipped an evaluation system into Europe.

www.pre-switch.com

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Picture: 
The 200kW SiC inverter evaluation system from Pre-Switch

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