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

While the initial interest is in improving the efficiency of low-cost IGBT-based inverters, the technique can be applied to SiC and GaN-based topologies to reduce the size of the inverters further. “We think high switching frequency will be a key differentiating technology; we can work with GaN and we have done SiC at 1 MHz,” Renouard says. “It’s all about the dv/dt in the wires of the motors – we make the edges very smooth, we slow down the edges and speed up the transitions to reduce the current in the system so the conduction losses are low, but the switching losses stay the same. With pre-switch, there are no switching losses so there is no fall-off as the load increases. “We can work with other switching architectures – we are not tied to PWM, although we have a customer looking at a DC-DC converter project for its smallest electric truck.” Safety The UnitedSiC cascode devices have moved from OBC and DC-DC designs to inverters. “These are used in traction inverters with sophisticated control schemes,” says Dr Chris Dries, CEO of UnitedSiC, which is now part of Qorvo. “The low on-resistance of the JFET cascodes allows us to really exploit areas of functional safety to provide circuit protection,” he adds. “For example, rather than having a mechanical switch creating the connection between the high-voltage switching and the electronics, you can replace it with a solid-state switch using the cascode. “We have a number of designs in the US and Europe all using our discrete devices in 400 V inverter designs, with the 750 V devices with 5.9 mΩ on- resistance, and in 800 V inverter designs with 1200 V-class devices.” This is increasingly being adopted in industrial EVs such as forklifts with a 400 or 500 V inverter using a phase shift full- bridge topology. Conclusion Advances in powertrain design come from a combination of wide-bandgap materials such as GaN and SiC, new device combinations such as cascodes, new topologies and new controller architectures. All of these can be used in different ways to reduce the parasitic losses that lower the efficiency of the inverter and the bidirectional onboard charger. The controllers can boost the performance of the switching of silicon IGBT transistors to boost the performance of existing topologies, and can be used with new topologies to provide higher efficiency across the whole load profile of a powertrain. New transistor devices using SiC can handle higher power with lower losses and higher frequencies than IGBTs and superjunction MOSFETs, while depletion- mode GaN transistors can switch in the MHz range. These higher switching speeds can reduce the size of the magnetics used in topologies such as totem poles for OBCs and Vienna rectifiers for on-street chargers. That helps to reduce the size and weight of the OBCs, reducing the weight of a vehicle and improving the efficiency of the fast chargers. Deep insight | Switching A 200 kW inverter design using pre-switch control (Courtesy of Pre-Switch) 62 Winter 2021 | E-Mobility Engineering