Maximum Voltage, Maximum Safety

The flexPi bidirectional interface provides access to the high-voltage system in vehicles

With their high-performance high-voltage batteries, hybrid and electric vehicles could also supply external power consumers. However, handling 400 volts is somewhat more complicated than connecting up to the 12-volt vehicle electric system through the cigarette lighter. This is why IAV has developed flexPi: The universal high-voltage interface for the vehicle is not only safe but also bidirectional – and, among other things, suitable for connecting range extenders.

Connect the plug when needed, simply unplug it again later on: What is done so easily at home at the 230-volt power socket or at the cigarette lighter in the vehicle, is no longer possible for 400 volt direct current. Before current starts to flow, the interface must check, for example, if the insulation of the connected power consumer is in proper working order. And anyone who simply unplugs the connection afterwards risks an intermittent electrical fault – for this reason, the electronics must first ensure a safe state before unlocking the plug.

All this is done by flexPi, the flexible power interface IAV has developed as a universal high-voltage interface for the vehicle. A comprehensive test program runs through as soon as a power consumer is connected – starting with measuring insulation resistance and then checking voltage, current, temperature and plug lock through to testing the digital communication between high-voltage source and load. Pressing the “ON” button initiates precharging with current and voltage measurement, followed by operation with permanent monitoring. IAV’s own universal control unit is responsible for this and powerline communication with the power consumer. It also makes sure that, after switching off, all of the power consumer’s capacitors are discharged in a controlled manner – to avoid sparking on unplugging and prevent dangerous voltage at the plug.

Extended cruising range for the weekend trip

Once introduced into production, flexPi can open up many new applications. “Tradesmen could operate their work machines or firefighters their pumps on 400 volts from their hybrid or electric vehicles”, says Markus Steinhauser, head of the High Voltage and Components department at IAV. “It could also be used to supply power to mobile homes or highperformance battery chargers. Even the power supply for a home could be provided for some time from a vehicle’s high-voltage battery.” But flexPi is not only a reliable power supplier. As the interface is designed for bidirectional use, it can also feed energy into the vehicle. Owners of an e-car could use it, for example, to connect an additional battery pack to their vehicle to get a greater traveling range for a weekend trip.

IAV has been working on the flexPi concept since 2013. In the meantime, a demonstrator is available with control unit and CAN bus interface. IAV has already tested the box in a Renault Twizy and, as the next step, will be constructing a demonstrator auxiliary power unit. “Above all, we see huge opportunities in the commercial vehicle segment”, Steinhauser says. “Trucks with electrified powertrains have been around since 2010, and by 2020 most manufacturers will be putting models of this type on the market. Agriculture has also come a very long way in this regard and has defined appropriate interfaces.” Some Japanese passenger cars already have 400-volt connection capabilities for power consumers. So, there is huge interest in high voltage from the vehicle – as also confirmed in initial talks that IAV has already had with customers about flexPi.