Better Motors, Better Power Inverters = Better Electric Cars

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As much as we write about the EV revolution here at CleanTechnica, you might think the EV revolution is over, but it is just getting started. The first automobiles were crude devices — loud, smelly, and fragile. Today’s cars have the benefit of more than 100 years of development, a process that has made them quieter, more efficient, and reliable. The development process for electric cars and trucks is just getting started and will result in more sophisticated technology that will make those vehicles more efficient, more reliable, and less costly. Here’s news about two developments you should be aware of.

Fraunhofer’s Improved Power Inverter

Electricity comes in two flavors — direct current and alternating current. Batteries are DC devices, but the electricity to recharge them is AC. Most electric motors for cars and trucks also operate on AC. Something has to do the job of converting one form of electricity to the other and back again in order for electric cars to function. That something is called a power inverter.

While power inverters are essential to the process, they also have a significant drawback. They are not 100% efficient, which means every time the conversion process takes place, some of the electricity passing through the device is lost, usually as heat. Those losses can add up over time, resulting in shorter range. Just as mechanical engineers have figured out how to make gasoline and diesel engines more efficient, electrical engineers are hard at work figuring out how to make power converters more efficient.

The people at the reliability and micro-integration division of Fraunhofer Institute announced recently an improvement in power inverter design that could lead to a 6% increase in range for electric vehicles. The secret is using silicon carbine semiconductors which operate more efficiently. That in turn results in less heat buildup and more electricity available to power electric motors. SiC semiconductors are relatively expensive, however, which means the inverter should have as few as possible. Cooling those semiconductors therefore becomes critical. Frauhofer has redesigned the SiC power inverters to maximize coolant flow.

Fraunhofer says large amounts of current flow back and forth between the battery, the motor, and the power inverter when a vehicle is accelerating, braking, or traveling at high speeds. It is precisely under such conditions that most of the power losses occur. “We expect that by optimizing the drivetrain in this way, the range of electric cars will ultimately be extended by up to six percent,” says Fraunhofer’s Eugen Erhardt. 6% may seem trivial to some, but it is actually a big deal. When it comes to electric cars, that kind of performance boost can only be achieved by making the battery larger, which increases costs, or through a considerable amount of research and development, which is also expensive.

The engineers at Fraunhofer needed to create a mounting plate for the SiC semiconductors that is as thin as possible so the critical devices are close to the surrounding coolant. But thin mounting plates tend to deform under heavy loads. To solve that issue, the engineers use 3D printing techniques to create cooling fins that support the plate like the columns that support a dome.

Different materials expand at different rates when heated. When a power inverter heats up during use, those different expansion rates can cause cracks to occur within the structure of the inverter. The new 3D-printed cooling element solves this problem as well. Because the metal mounting plates are extremely thin, they are able to compensate for the stresses that occur as they are heated or cooled by deforming slightly. This flexibility spares the expensive SiC semiconductors and extends their service life.

But Fruanhofer isn’t done improving power inverters. Rather than connecting them to the rest of the power train components in the usual way by using solid copper conductor tracks, it links them to the rest of the electronic system by stranded, flexible, fine copper wires.

“We still have some way to go before the device is ready to go into production,” says Eugen Erhardt. “In the first instance, we are pulling everything together to create a prototype. The individual process steps will then need to be further optimized.” Those prototypes will be tested by Bosch over the next several months before being installed in Porsche electric cars whose powertrains have been precisely matched to the silicon carbide equipped inverters.

High Power Compact Electric Motor From EVR

The Israeli startup EVR Motors says it has created a new electric motor design that is half the size of a conventional radial flux motor while weighing 10% less. “We managed to improve the basic design of the electric motor, which has remained largely the same over the past few decades, while maintaining the traditional advantages of radial flux motors,” says Opher Doron, CEO of EVR.

The company calls its new motor TSRF, which stands for Trapezoidal Stator Radial Flux — a permanently excited machine with 3D trapezoidal teeth and windings. It says the TSRF  “generates an increased magnetic flux and reduces the leakage flux” and is expecting to begin series production later this year. The new compact motor, with its improved cooling, has greater power and should benefit from lower production costs. It can work with voltages from 48 to 800, is capable of either liquid or atmospheric cooling, and can be adapted to various types and sized of magnets.

EVR says it is in talks with a number of manufacturers and suppliers. An air-cooled prototype designed for use in 2- and 3-wheeled vehicles weighs just 9 kilograms and has 17 kW of power to go with 40 Newton-meters of torque. Other prototypes that use liquid cooling, different voltages, and ferrite magnets instead of neodymium will be tested in the months to come.

EVR claims its new engine architecture can be adapted to “most mobility and industrial applications.” It is working to develop larger prototypes that will be suitable for passenger cars and commercial vehicles and get them into the hands of manufacturers and OEMs as soon as possible.

Baby Steps

More efficient power converters and smaller motors — the EV revolution will depend on such tiny improvements. Whether it is batteries or other components of electric car powertrains, what is cutting edge today will be obsolete tomorrow. The challenges will keep engineers up at night, but drivers will be the beneficiaries as the cars get better and better. We can’t wait!


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