In 1978 Honda ran commercials crowing that its uncatalyzed CVCC engines weren’t “choosy” about their fuel—they could run on regular leaded, premium leaded, or unleaded gasoline, so “you can be the one who’s choosy.”
Fast forward to today’s version of emerging technology, in which electric vehicle owners hope their current vehicles’ existing plug design, hardware, and software will be flexible enough to take full advantage of quicker charging options as they come online. Continental’s new AllCharge concept aims to assuage these anxious EV owners by emulating the CVCC’s omnivorous refueling appetite for electric charging as voltage and power levels evolve.
Before we tackle the new tech, let’s review how “normal” EV and PHEV charging works: A charger integrated into the onboard power electronics system accepts 110- or 220-volt AC wall current and “rectifies” it to DC current at the voltage required by the battery pack. These typically operate at a maximum rate of between 3 and 10 kW because higher current rates increase thermal loads, requiring a much larger cooling system. The fastest charging rates (e.g., 50 kW SAE, 120 kW Tesla Supercharger) handle the heat-intense AC-to-DC conversion off-board in a big, heavy, expensive charging station so all the car has to do is raise or lower the voltage level to whatever the battery uses.
Of course, during deceleration and braking all these electrified vehicles are able to run their motors and power inverters backward to put energy back into the battery. A lot of times that energy is going back into the system at well above 10 kW. So why not use this same pathway to charge the battery (potentially way more quickly) and ditch the mass and cost of the extra charger?
That was the inspiration for AllCharge—and in designing the system Continental managed to find some additional windfall benefits. Because the motor generates AC current, Level 1 and 2 electricity flows in through the stationary motor at rates that could potentially be as high as 43 kW if three-phase AC chargers ever appear in North America. The motor serves to filter out “dirty electricity”—noise generated by nearby fluorescent lights, dimmer switches, and the like. The inverter rectifies this clean power from AC to DC and then a “DC-DC Booster” delivers this power to the battery at the voltage it prefers (400 volts in the Conti demo vehicle). That DC-DC Booster is also able to accept incoming fast-charge current at up to 800 volts and 150 kW (with the potential for 350 kW if chargers become available and batteries someday prove capable of charging at that rate).
Why not use this same pathway to charge the battery (potentially way more quickly) and ditch the mass and cost of the extra charger?
Integrating the DC-DC device into the power-flow system has benefits even when unplugged. Because power equals voltage multiplied by current and because high-amp current flow generates heat, power can be more efficiently delivered at higher voltage and lower amperage. For this reason the DC-DC Booster can maintain 800 volts when supplying power to the motor. This constant voltage level promises to reduce stress on power inverters. Today power inverters generally operate at battery-pack voltage, which can vary widely with state of charge (a nominal 400-volt battery can swing between 470 and 270 volts). This also means that drivers of an AllCharge-equipped vehicle should experience no drop-off in performance as the battery nears the end of its charge.
Forcing the drivetrain inverter to manage all charging duties adds stress to that unit, though Conti points out that wall power is far more consistent than regen-braking power. Coping with the extra heat generated by the highest power-flow rates requires upgrading from plain silicon to costlier silicon-carbide diodes and switches, but these costs are more or less offset by ditching the onboard Level 1/2 charger, leaving costs competitive with a fast-charge-equipped EV. The SiC diodes help maintain roughly the same charging efficiency as today’s systems, as well.
Bottom line: As long as the plug and/or adapters fit, choosy AllCharge drivers should be able to take advantage of whatever charging rate best meets their needs.
llustration: Martin Leon Barreto