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

boost converters with support for the high currents for heaters and air conditioning, each typically around 5 kW. The DC-DC converters use silicon MOSFETs and have an efficiency of around 97%. Feeding 10 kW of power to a coil has to be handled without disrupting the base electrical system, and to regulate that power requires a specialised, air-cooled power controller that can be placed in different areas of a commercial vehicle design. This would typically be placed close to the battery pack to operate at the 65 C ambient temperature without the need for a fan. Motor designs For mild hybrids, the electric machine tends to be an induction motor rather than a permanent magnet (PM) type, as the torque requirement is less, although car makers are looking at alternatives to induction motors to increase the power and torque density to achieve the target power density of 100 kW/litre determined by US requirements. These include interior PM (IPM) motors and other switched reluctance motors (SRMs), and there is academic research into IPM and SRM technologies. SRMs have traditionally not been used as they have noise and vibration issues, and the torque is not as high as with an IPM as there is no magnet, but there are cost benefits as a result. The key advantage of 48 V is that it is a low-voltage design, below 60 V. Above 60 V, all the requirements in the inverter change, so there are regulations that need to be considered for HV, such as isolation, clearance and creepage. In an actual application the voltage in transient events may exceed 60 V but discharge circuitry is added to keep the voltage below that to avoid the creepage and clearance requirements that come with higher voltage designs. The switching technology of silicon MOSFETs from 80 to 100 V is also much cheaper than IGBT, silicon carbide (SiC) or GaN devices and easier to validate. MOSFETs are well- understood in switched-mode power supplies so there is a lot of expertise around, and they are very reliable. As the power goes up in the motors there is an increasing need to cool not only the stator lamination but the coils as well, in the form of oil cooling splashed onto the end windings of the stators. However, this means adding a pump and other structures, so it makes the design more complicated. 48 V motors are currently rated to 50-60 kW but at 100 kW and beyond the design becomes more similar to battery EV motors and oil cooling becomes more critical. 48 V compressors The move to 48 V and experience with electric motors in mild hybrids also provides a boost to other parts of a hybrid vehicle’s powertrain. The latest generation of 48 V compressor, or e-booster, for a turbocharger can improve the efficiency of an IC engine to reduce emissions, as it can be made smaller. The e-booster’s design provides major improvements in efficiency and performance, maximising efficiency at low loads. Higher engine power output is achieved by separating electrical boosting from the turbocharger so that it can be matched to higher power, enabling lower back-pressure in the exhaust manifold and improving gas exchange. This second generation of e-booster supports continuous power of 2.5 kW up to a maximum of 7 kW, compared with the first generation that enabled transient boosts up to 5 kW for 20 seconds per minute using a permanently excited synchronous motor (PMS). This reduced the energy requirement during acceleration substantially compared with a traditional reluctance motor. The PMS also significantly improved both noise, vibration and harshness and engine response, along with torque density and efficiency. The second-generation e-booster continues to use a PM motor but reduces the moment of inertia of the rigid rotor and compressor with a higher current of 160 A, up from 130 A, and faster spool-up of 190 ms, up from 270 ms. The design has a new EMC choke for lower power losses and enhanced filter effect, a stator linked to the power electronics for reduced resistance and improved efficiency, a microcontroller with added computing capacity for field-oriented control (FOC) and Focus | 48 V systems Switched reluctance motors are being investigated for 48 V systems (Courtesy of Dana) 34 Winter 2021 | E-Mobility Engineering