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Power Electronics and Electrical Machines

Advanced electric drive vehicles such as hybrid-electric vehicles, plug-in hybrid electric vehicles, fuel cell electric vehicles, and pure electric vehicles, require power electronics and electrical machines (PEEM) to function. These devices allow the vehicle to use energy from the battery to assist in the propulsion of the vehicle, either on their own or in combination with an engine. Figure 1 is a simple diagram of an electric system drive, where the inverter (power electronics) takes direct current (DC) electricity from the battery and converts it to alternating current (AC) electricity and sends it to the motor. The electric motor (electric machine) uses the AC current to create torque (mechanical power) to power the wheels for propulsion. Note that the arrows point both ways; this is because the electric machine can also act as a generator and help the vehicle slow down when coming to a stop. This sends energy back through the inverter and into the battery to recharge it.

Diagram of a simple electric drive system

Figure 1. A simple diagram of a HEV traction drive system.

Figure 2 is a diagram of a more complex PEEM system in a plug-in hybrid electric vehicle. This vehicle uses two electrical machines; one as a generator connected to the engine and another as a motor to drive the wheels. Each of these machines is connected to an inverter, and the two inverters run at a higher voltage than the battery. To achieve this high voltage, another power electronics device called a boost converter boosts the battery voltage before sending the DC electricity to the inverters. Notice that the battery charger is considered a power electronics device, as are all of the blue components, and that all of the components inside the dashed box in Figure 2 could be replaced by a hydrogen fuel cell to create a fuel cell powered PHEV. Key components for hybrid and electric vehicles include motors, inverters/converters, sensors, control systems, and other interface electronics.

Diagram of a more complex PEEM system in a plug-in hybrid electric vehicle

Figure 2. A more complex diagram of PEEM in a plug-in hybrid electric vehicle (PHEV).

Advanced technology vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), fuel cell hybrid electric vehicles (FCHEVs), and electric vehicles (EVs) can help meet important DOE goals, such as petroleum reduction. However, modern day PEEM technology is not sufficient to enable market viable PHEVs, FCHEVs, and EVs. So, the Vehicle Technologies Program aims to develop these technologies by setting strategic goals for PEEM, and undertaking research projects that are carried out through collaboration among government, national laboratories, academia, and industry partners.

Achieving the PEEM goals will require the development of new technologies. These new technologies must be compatible with high-volume manufacturing and must ensure high reliability, efficiency, and ruggedness. These technologies must also reduce cost, weight, and volume. Of all these challenges, cost is the greatest. PEEM project partners work together to ensure that technical attributes, vehicle-scale manufacturing, and cost sensitivities are addressed in a timely fashion and that the resulting technologies can be adopted by companies willing and able to supply products to automakers.

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