Exploding the inverter

Mahindra Racing Formula E M3Electro inverter Current E

Electric racing has introduced a whole new way of thinking about powertrains to many fans. While the battery and the motor may be relatively easy concepts to understand, what on earth is an inverter – and, more importantly, how can it deliver a competitive advantage? We sat down with Angus Lyon, head of powertrain at Mahindra Racing, to provide some clarity.

First things first: what is an inverter?

“The inverter is the module which controls the electric motor. We need this to make the battery and motor work together. The motor is a three-phase AC unit which requires a complex-shaped voltage waveform to make it operate. The battery, however, is a fixed-voltage DC supply. The inverter generates this voltage profile to make the electric motor work and produce the power required. In Formula E, you would have seen this as the little box that sat on top of the battery in all season one cars.”

It’s pretty important then?

“If you were to compare an electric powertrain to a conventional internal combustion engine (ICE), the inverter is like the engine management unit (ECU). The ECU controls the fuel, air and sparks to make the ICE produce the power required, with the right characteristics. It is a vital part of the system. The electric motor is really a pretty simple, dumb unit which wouldn’t work on its own. The inverter is what makes the whole thing work. No inverter, no speedy racing car.”

Do all Formula E teams use the same inverter?

“In season one there was a single type of inverter which all teams had to use. From season two onwards, teams could specify their own inverters. Teams use one or two inverters, depending on the configuration of their motor setup. Inverters have evolved over the past two seasons to reduce weight and improve packaging, as well as to boost control accuracy, response and overall efficiency. More recently, some teams are starting to experiment with cutting-edge, next generation electronic materials (such as silicon carbide) to further improve efficiency and reduce weight.”

Where are the inverters located?

“The inverter sits between the battery and motor in the electrical circuit so there are limited places where it can be located. Teams typically mount the inverter on top of the battery or in the rear of the car. Designers try to keep the distances between each of the main units – battery, inverter, motor – as short as possible to reduce the amount of heavy copper cable which connects them.”

What can you tell us about the Mahindra Racing inverter?

“The inverter is vital to the control and efficiency of the overall powertrain. Our inverter is manufactured by Magneti Marelli, as is the electric motor. We worked closely with Magneti Marelli on the design of the inverter as well as that of the electric motor. By developing both with the same team, we could ensure that they are fully optimised for each other and as part of the overall powertrain. Our inverter is encased in a lightweight aluminium housing and uses the latest electronics technology – but that’s all top secret.”

Electric cars have been around a long time, so don’t we already know how to make the best sort of inverter?

“Generally, inverters are quite mature in the fundamental layout and architecture of their design but the detail of the electronics, software and mechanical packing (including cooling) is developing rapidly now that Formula E is pushing the technology. Inverters have existed for decades but the requirements have been fairly low-stress, with more emphasis on low cost and high-volume manufacturability. With Formula E, inverter design is moving forwards with new technologies, much more optimised designs and incredibly complex and intelligent software control algorithms. This is driving inverter technology development at a much faster rate than even just few years ago.”

Will these lessons translate to road cars or are they specific to racing?

“For Formula E, there are further technologies in inverter electronics, cooling and control to come in the next few years, which will further improve efficiency and reduce size and weight. The technologies being developed in Formula E will slowly migrate to on-road electric vehicles and will make them more affordable. So yes, the lessons and technologies translate to making better road cars.”

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