Porsche Unveils AC Battery Technology

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According to legend, on New Year’s Eve, 1899, the head of the US Customs office announced, “Everything that can be invented has now been invented.” His statement missed a few things, like space travel, nuclear weapons, and the internet, but it did ultimately teach us a valuable lesson about assuming human ingenuity has reached its limits. Take, for example, the battery systems that power electric vehicles. Batteries store electricity as direct current (DC). That’s why EVs need inverters to convert the alternating current (AC) prevalent in most homes and commercial buildings to DC that can then be used to recharge their batteries. But many of the electric motors that actually power our EVs run on AC.

We assume China is the leader in all things having to do with battery technology, mostly because CATL and BYD are the two largest battery manufacturers in the world. So, it is rather surprising to read in the latest press release from Porsche that Porsche Engineering claims to have developed an “AC battery” for electric vehicles that combines numerous components into a single part. It features a standardized control unit with a particularly powerful real-time computing platform. The system was developed as part of a feasibility study, but has been tested in the laboratory and demonstrated in an actual vehicle.

Porsche says the drive system for an electric vehicle usually consists of several separate components — a high-voltage battery, a battery management system, power electronics for controlling the electric motor, and an onboard charger for charging with AC power. In this new technology, the power electronics use a pulse inverter to convert the DC voltage of the battery into the sinusoidal three-phase AC voltage needed to power the electric motor or motors that turn the wheels of the vehicle.

“The trend in the automotive industry is toward highly integrated components,” says Thomas Wenka, a specialist project manager at Porsche Engineering. “This opens up new possibilities in terms of housing size, weight and cost reduction, reliability and efficiency.” His development team has created an AC battery platform that integrates the separate functions of the battery management system, pulse inverter, low-voltage DC, and onboard charger into one single component.

To do that, Porsche Engineering divided the high-voltage traction battery into 18 individual battery modules, distributed over three phases that are controlled individually by semiconductor switches. The flexible interconnection of the individual battery modules into a Modular Multilevel Series Parallel Converter (MMSPC) enables dynamic modeling of the voltage curve so that the sinusoidal three-phase AC voltage for the motor can be generated directly by the DC voltage from the battery modules. “With the MMSPC, both the direct control of the electric drive motor while driving and the direct connection to the AC grid for charging the battery is possible,” says Daniel Simon, a project manager at Porsche Engineering.

Other advantages include easier scalability to power various drivetrain variants as well as safer handling of current carrying components during servicing. In the event of an accident, “The MMSPC is switched off and the system effectively reverts back to its individual modules, meaning that only the module voltage can still be measured,” says Wenka. In addition, failure protection increases in the event of a possible defect in individual battery cells because the intelligent control system bypasses the affected battery module. That makes a so-called limp home function possible so a partially disabled car can be driven to the nearest repair facility, albeit under reduced power. With a conventional battery, such a failure would cause a complete vehicle breakdown. The AC battery platform also offers the potential for rapid replenishment of the traction battery via pulsed charging.

Porsche Shows Its Battery Management Prowess

A major challenge in implementing the AC battery concept was the development of a powerful and fast central control unit that can precisely control the individual battery modules. “Dynamic reconfiguration of the battery modules in sine wave modeling is made possible by the underlying distributed system, which must meet real time requirements under all circumstances,” says Simon. “After all, a delay in switching the modules would lead to defects in the battery packs and the associated power electronics.”

“The processing unit represents a heterogeneous multiprocessor platform and runs as a single system-on-chip. It combines a field programmable gate array (FPGA) — an integrated circuit with programmable hardware — for data control and monitoring with regard to the real-time capability of the system, and a powerful multicore processor for processing large amounts of data in a single component,” explains Simon.

“The FPGA can take over complex calculations to relieve the processor and supplement missing peripherals, which are significant advantages in terms of scalability and flexibility compared to the usual pure microcontroller solutions. And by selecting the derivative within the system-on-chip family, the performance can be scaled from basic ECU requirements such as  an I/O driven communication gateway or power electronics — to complex ADAS systems with additional GPU and video codec requirements.”

One special feature of the approach is the software-focused implementation of the control unit functions. “One part runs on a processor, which uses the FPGA for fast control and the optimal switching strategy, and ultimately controls all modules synchronously. This enables dynamic reconfiguration through software. However for that to work, the power electronics on the modules have to implement this switching strategy,” says Simon. “By using a systemon chip approach with a CPU and FPGA, we enable hard real time capability that cannot be achieved with normal micro-controllers.”

The Takeaway

To be honest with you, dear readers, I have no idea what all that jargon means. This press release is obviously written by some very smart and capable engineers, but much of it is way over my head. Suffice to say that Porsche, which has a long and proud history of engineering excellence, has devised new ways of controlling the many components of an electric vehicle platform. For years, we have been saying that it took a century to perfect the internal combustion engine, and we are likely to see a similar pattern of constant innovation when it comes to EVs. This latest news from Porsche proves that point. Though, it seems unlikely most of us will be able to tell the difference from the driver’s seat.