Shifting to 800-volt systems: Why boosting motor power could be the key to better electric cars

The latest results from research on 800-volt battery-driven vehicles show that this could lead to smaller, lighter, and more environmentally friendly motors. Cars using these powertrains could also be charged faster and travel further on a single charge

Sales of electric vehicles are slowly beginning to gain traction in Europe as mainstream brands including Volkswagen, BMW, Fiat, Opel and Hyundai start to roll out battery-powered models.

But, despite a push by many governments to ban sales of new petrol and diesel cars in the next two decades in favour of full-electric vehicles, the existing technology in battery vehicles restricts their ranges and makes them more time-consuming to refuel than their combustion-engine rivals. This and their higher price continue to hamper their chances of becoming mainstream any time soon.

For many industry observers though, developments to boost the electrical systems of battery-driven vehicles to 800-volts from the current industry standard of 400 volts could be the breakthrough that finally allows electric vehicles to move to the next level and better compete, and eventually replace, combustion vehicles. A necessary transition as Europe strives to lower vehicle emissions and tackle climate change.

Professor Peter Wells, of Cardiff University's Centre for Automotive Industry Research, says: "As is usually the case with 'premium' technology options in the automotive industry, we can expect a rapid transfer to the mass market arising from competitive pressures. In some cases, manufacturers have designed-in the ability to migrate from 400 volt to 800 volts as costs fall and as competitiveness comes to require such systems."

Among those companies who have already embraced this technology is Volkswagen Group's sports car brand Porsche, who have fitted an 800-volt system in their full-electric Taycan sports car, which was launched last year. For Otmar Bitsche, director of e-mobility in the automaker's research and development unit, the reasons for opting for the higher-powered unit are clear: "Lower weight, higher efficiency and faster charging" are the major benefits to 800-volt systems, he believes.

Charging time can be greatly reduced when using fast chargers capable of working at up to 270 kilowatts. "If the charger provides 800 volts and a minimum of 300A, the Taycan can charge from 5% to 80% in 22.5 minutes. 400V chargers typically provide 50kW only. The same charging capacity would need 90 minutes," Bitsche explains. The automaker, which was the first to introduce an 800-volt electrical system commercially, claims a 420-kilometre range between charges for its four-door coupe-styled saloon.

While this is not hugely higher than figures achieved by rivals using 400-volt systems such as the I-Pace from Jaguar, which can cover the 354 kilometres on a single charge, the use of an 800-volt system considerably increases the possibilities to boost the range of their electric vehicles.

One such advantage is that 800-volt electrical systems allow a greater retention of power, which is normally lost through heat generated during the charging process. A higher voltage system allows a lower current to be used when charging the battery, which reduces overheating and allows better power retention in the system. This power can be used towards a longer driving range.

Higher voltage systems also offer a number of key weight- and mass-saving advantages. The reduction of copper is one of these. Electric motors are much simpler than combustion engines in construction and at their core they have a rotor, which turns in response to a rotating magnetic field created by electricity from the battery. To achieve this, electrical systems often use up to four times the amount of copper found in combustion engines. Using higher-voltage systems can lead to the amount of copper used in motors being significantly cut.

Michael Burghardt, senior project manager at AVL, a German company developing and testing powertrain technology for cars and trucks, says: "Higher voltages mean less current and less current means less copper in the car. Less copper means less weight, and this is the goal we are reaching for."

Burghardt is collaborating with the European Union research project Drivemode, which is seeking to develop a highly efficient and compact modular drivetrain for full-electric cars that uses the vehicle's stored energy more efficiently through a higher-voltage electric system.

Besides reducing the weight of motors, an 800-volt system has the added advantage of reducing their mass too. Since the higher voltage allows the motors to run at speeds of 20,000 rpm, well over double that of their 400-volt siblings, they have better power density. This means that they convert electrical power to mechanical power with this speed and not high torque.

"In general, motor size is defined by torque capability," Bitsche says, which means removing torque from the equation allows motors to be much smaller. So much, in fact, that smaller high-speed motors can weigh as little as 25 kilograms, with the result that they reduce the overall weight of a vehicle, enabling it to travel much further on a single charge.

Watch the video interview on high-voltage systems in electric vehicles with Michael Burghardt—AVL, Germany
https://www.youtube.com/watch?v=_-lFQ_k-QJ0

Smaller motors also mean the vehicle has additional space for batteries as Professor Wells notes: "The reduced weight of 800-volt systems will further help with increased range and acceleration performance or allow for larger battery packs with even greater range."

Reducing the size of the motors along with optimising the efficiency of the drivetrain is central to Drivemode's goal of producing small adaptable electric modules that consist of power electronics, a gearbox, and the motor itself. Modules that can be scaled up according to the power requirements of a given vehicle.

"The intention of the Drivemode project was to have one motor which can fit in different modular systems having one to four motors in one car," Burghardt says.

That goal is one of many technical challenges that the project has met and overcome since it was launched. Technology derived from Drivemode is now expected to make its way into production vehicles in the next few years as the auto industry makes the move to the next generation of electric vehicles.

According to Professor Wells, the 800-volt technology will take a couple of model generations to really filter through to becoming the de facto standard, but by 2026 it can be expected to be the dominant application.

Provided by iCube Programme