ISSUE 012 Winter 2021 Sigma Powertrain EMAX transmission dossier l In conversation: David Hudson l 48 V systems focus l 2021 Battery Show North America and Cenex-LCV reports l Everrati Porsche 911 digest l Switching insight l Motor laminations focus

and require a monitoring accuracy of under 2 mV to accurately determine cell ageing. Using a dedicated data acquisition path for each cell allows the voltage of all the cells to be measured at the same time, with the voltage and current synchronised by using 15 analogue-to-digital converters (ADCs), rather than using shared resources. This monitoring is used for the functional safety requirements to determine over- and undervoltage, overheating or overcurrent. A cyclic redundancy check on the ADCs for cell monitoring ensures the accuracy, and if an ADC is not accurate enough, the monitor can move to a shared, round-robin scheme for a ‘limp home’ solution. Intelligent power distribution One of the major trends for 48 V power distribution is the replacement of relays and melting fuses with semiconductors for an intelligent power distribution system. For safety-critical applications such as ADAS driver assistance, electronic fuses are faster, at 100 µs, than traditional fuses at 20-50 ms, as well as smaller, so the electronic version reduces the fuse box’s dimensions and weight. Electronic fuses are also fault-tolerant, and can be reset after being triggered rather than having to be replaced. The fuses are ‘load shaped’, where the cable can be sized to the current and voltage characteristics rather than typical or standard wires. The latest devices can emulate the profile of a fuse to protect a PCB trace, a connector and/or wires from overheating without any impact on the load transients or current management. The fuses use a silicon MOSFET as the actuator and allow every power line to be intrinsically protected by the switch using a 5 x 5 leadless device that can still handle up to 300 A. DC DC converter Using 100 V GaN transistors for a high- density 48 V DC-DC power converter enables a system that is one-third smaller and 50% lighter than standard converters, and that has an overall efficiency of more than 95% compared with silicon-based designs. The converter has an input voltage range of 24-60 VDC and is rated at up to 1 kW of continuous power with an efficiency of 97.5% at full load – a 4% improvement on similar types of converters currently on the market. The power density is 28 W/cu in compared with 10 W/cu in in converters using other topologies and switches, and the design without the case weighs 345 g. Testing Testing the integrated starter/generator (ISG) is a key challenge. It is mounted between the flywheel of the engine and the transmission, and replaces the starter motor and alternator to provide hybrid functions such as boosting, energy recovery, load point shifting, coasting and start/stop, in P3 and P4 hybrids. Current and voltage measurements at the input of the inverter are needed to obtain the optimum parameters for the starting operation. Although the onboard supply voltage has been increased to 48 V, currents up to 300 A still occur. In situations such as engine start-up, there are even higher current peaks, which can seriously damage the 48 V battery. That means it is important to precisely measure the steady current and the peaks, which might last for only a few microseconds. To perform measurements as close to the inverter as possible, a current sensor is mounted between the back- up fuse and the ISG. The measurement module and data collecting gateway are placed in the footwell of the passenger seat. The power electronics of the ISG also contains a current sensor that is checked via CAN bus. The comparison clearly shows that the internal sensor is operated at a far lower sampling rate. In addition, there is a distinctive signal delay owing to the lower bus performance. A bandwidth of 100 kHz allows current peaks to be converted into high-resolution voltage signals. Contrary to conventional current sensors such as shunts, a Hall effect current sensor is inherently galvanically isolated from the measurement set-up, which means that there is no risk of a short-circuit. This electronic fuse combines the MOSFET and controller in a single package with a 4-48 V input (Courtesy of STMicroelectronics) 38 Winter 2021 | E-Mobility Engineering