Porsche Engineering has developed what it is calling a concept for an ‘AC battery’ which integrates the normally separate functions of the battery management system, inverter, low-voltage DCDC and onboard charger into one single component, controlled by a standardized control unit concept with a particularly powerful and real-time-capable computing platform.
“The trend in the automotive industry is toward highly integrated components,” said Thomas Wenka, specialist project manager at Porsche Engineering. “This opens up new possibilities in terms of housing size, weight and cost reduction, reliability and efficiency.”
For the study, the developers at Porsche Engineering divided the high-voltage battery of the electric drive into 18 individual battery modules, distributed over three phases. These are controlled individually by power semiconductor switches. The flexible interconnection of the individual battery modules into a modular multilevel series parallel converter (MMSPC) as a distributed real-time system enables dynamic modeling of the voltage curve, so that the sinusoidal three-phase AC voltage for the motor can be generated directly from 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,” explained Daniel Simon, specialist project manager at Porsche Engineering.
According to Porsche Engineering, advantages of the system include easier scalability to various drivetrain variants as well as safer handling of current- carrying components during servicing or in the event of an accident.
“Then 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,” added Wenka.
In addition, failure protection increases in the event of a possible defect in individual battery cells, as the intelligent control system bypasses the affected battery module. This makes it possible to implement a so-called limp-home function to the nearest workshop with reduced power. With a conventional battery, this would cause a vehicle breakdown.
The concept of the AC battery also offers the technical potential for a fast-charging capability capacity through pulsed charging.