process, not least because you’re going from CAN bus through a Linux software system into the powerline communication bus, and then back,” Hazell says. “Back in the days of CHAdeMO, it was all just CAN bus comms, which kept things easy. But now that effective charging takes conversion between one comms protocol to another, it’s become a much more technical field, and the required software stack has become larger and more complex. So, we source a solution from IoTecha, which handles that portion of the process, but separately, our contactor control system has to do all the other work to enable IoTecha’s module to function.” That other work includes extracting charging-critical data from the BMS, and translating it into maximum, minimum and other requirements on power, voltage and current, which form clear and simple instructions for the charger to follow (fast-charger systems being comparatively simple devices, the burden is often entirely on the vehicle to select and request the correct delivery rate of electricity). “There’s further complications in that the EV needs to vary its metrics and instructions sent to the charger, based on the information it draws from the charger,” Hazell says. “For instance, we found out recently that if a charger ‘tells’ you it can only output a maximum of, say, 100 A, you need to ask for 100 A specifically, because if you ask for more, the charger might react by shutting down since it can’t fulfil what you’re requesting. There are many similar issues that we’ve had to handle, so the battery outputs the relevant signals, based on the feedback from the IoTecha unit.” The contactor controller in Fellten’s pack also controls LEDs for starting, continuing and stopping a recharge session, and a lock pin that prevents the driver from pulling out the charge port during charging and the ensuing arcing hazard across the pins. Another LED is present for flashing code sequences to customers approaching the EV charge port; these sequences correspond to specific faults detected by the system, encompassing HV faults, lock motor faults and others explained in the EV owner’s handbook provided by Fellten. Fellten has developed its own system for pre-charging the HV bus. It was created to resolve issues with pre-charge scenarios, particularly when sensing whether vehicles had been pre-charged correctly, as standard timing- or inverterbased sensing approaches could sometimes cause pre-charge relays to burn out after time, or result in incorrect pre-charging or overheating of resistors during power-up. “Our system monitors the temperature of the pre-charge devices to ensure they don’t overheat and also performs live HV sensing. Our contactor controller board has HV sensors on it, tuned for accuracy to within 400 mV,” Hazell says. “As an EV comes alive, the system can make certain all the capacitors in the inverter and charger are full before we close the main contactors, so we don’t get a sudden spike from 0 to 400 V and blow out a set of components. Our system can sense within milliseconds if pre-charge conditions aren’t optimal – whether on one side of the bus or the other – and within a second it will shut off the main positive terminal to stop the pre-charge, so the rest of the surrounding subsystems can be brought up to the required standard voltage. “It won’t close the contactors until the bus is within 5 V of the source voltage. If the EV bus won’t get up to that voltage, then it normally means you’ve got a dead short, a grounding issue or something else wrong in the system. So, by doing it this way, we’re saving components in a lot of instances, because we then don’t risk blowing a fuse or melting a cable by shutting the contactors and allowing a dead short to happen.” Dossier | Fellten Morgan XP-1 July/August 2024 | E-Mobility Engineering 26 In addition to integrating IoTecha’s CCS device, considerable work went into engineering for safe selection and correct requests of electricity delivery rates
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