"In the early days of electromobility, the transistors in the power electronics switched at a fixed clock rate of between 8 and 10 kHz," explains Olaf Moseler, head of software function development for electric drives at ZF. Today, a fixed clock rate cannot meet the wide-ranging requirements for power electronics. This ultimately involves more than just supplying the electric motor with the alternating current it needs. It also entails a whole list of other tasks: The power electronics conversely rectify the electrical energy produced in generator mode during braking recuperation, feeding the energy back into the battery. Drivers who relish this sort of driving dynamics and play with the power pedal pose additional challenges through a combination of initial highpower demand followed by relaxed cruising. Plus of course the high expectations on comfort and good NVH behavior (NVH = Noise, Vibration, Harshness). And particularly the consistent demand for maximum efficiency, or a long range per kilowatt-hour to put it another way. "We now have a conflict of objectives – and there's no longer one 'right' switching frequency," says Moseler. If the transistors switch at high clock frequencies of around 14 kHz, that's ideal for dynamics. The current has a low ripple, i.e., undesirable rapid oscillations overlaid on a desired direct current, resulting in low losses in the electric motor. However, significant electrical losses occur with each switching operation on a transistor. High clock frequencies therefore lead to high energy losses in the power electronics. By contrast, low switching frequencies of around 2 kHz prove highly efficient but result in higher ripple currents and prove challenging in terms of acoustics.