2019-12-27
Vehicle Technologies – What’s Under the Hood? There are effectively two types of Electric Vehicle, all-electric vehicles (AEVs) and plug-in hybrid electric vehicles (PHEVs). AEVs, can be further classified as battery electric vehicles (BEVs) or fuel cell electric vehicles (FCEVs), both of which must be charged from the electrical grid and are also usually capable of generating electricity through regenerative braking. A BEV is propelled entirely by electric motors powered by on-board batteries, does not use an internal combustion engine hence does not rely on fossil fuel. During braking, the electric motor can function as a generator, recharging the battery by converting the vehicle kinetic energy into electric energy. In a PHEV, the internal combustion engine remains the main energy source, with the battery and electric motor used to improve overall efficiency; the PHEV is propelled by the electric motor when the ICE is less efficient and otherwise runs on the ICE. Again, during braking, the electric motor works as a generator, recharging the battery. Since they rely less heavily on the electric motor, PHEVs can use smaller battery packs than BEVs. In both the BEV and PHEV, a large battery provides current to high voltage components within the system, which supply the electric powertrain of the vehicle. The Inverter and the DC-DC Converter are key high-voltage sub-components within both types of vehicle; the inverter converts the DC current from the battery to the three-phase ac current required by the electric motor. The DC-DC Converter converts the high voltage generated by the vehicle motor, (during braking, for example), to the typical battery voltage, usually either 12V or 20V. The Inverter The power transistors used within an inverter must seamlessly convert, switch and regulate large amounts of high voltage currents in a high-temperature, hostile environment. Traditionally the domain of Insulated Gate Bipolar Transistor devices, (IGBT), new Wide Bandgap, (WGB), Silicon Carbide, (SiC), and Gallium Nitride, (GaN) based technologies are increasingly being adopted by manufacturers seeking improvements in power and efficiency levels. Transistors based on these technologies offer several advantages, including high temperature and high voltage operation and improved efficiency. At the same time, however, they bring new challenges to the designer in ensuring stable and safe designs. With the very fast switching speeds of GaN power transistors, great care must be taken to avoid the high levels of EMI emissions or transistor breakage that can be caused by parasitic inductance. While well-designed circuits and board layouts can address these issues, iterative design cycles can be time-consuming and expensive and tools such as Keysight’s leading-edge power circuit simulator software offer valuable performance verification during the design phase, greatly speeding time to market. The DC-DC Converter DC-DC Converters also bring design challenges; tradi...
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