Fraunhofer researchers hope to improve the efficiency of home charging
Researchers at Fraunhofer aim to enhance the efficiency of home charging. Charging with alternating current, whether through a regular household outlet or a wall box charger, often leads to significant energy losses. A consortium led by Fraunhofer IZM is now working to improve the effectiveness of charging using household electricity.
The challenge arises from the fact that the power grid operates on alternating current while vehicle batteries store direct current, necessitating a conversion process. In AC charging, this conversion occurs within the vehicle's onboard charger, which inevitably incurs energy losses. While differences exist between using an ICCB unit on household power and a wall box charger, neither completely eliminates these losses.
As part of the BMBF-funded 'EnerConnect' project, researchers from the Fraunhofer Institute for Reliability and Microintegration IZM, alongside the Technical University of Berlin, Delta Electronics Inc., BIT GmbH, and Infineon Technologies AG, are exploring a circuit utilizing innovative bidirectionally blocking GaN transistors-semiconductors made from gallium nitride.
Like silicon carbide (SiC), which is already partially used in electric vehicle power electronics, GaN semiconductors facilitate high switching frequencies, allowing for smaller and potentially less expensive components. However, conventional GaN transistors can only block voltage in one direction. In contrast, bidirectional blocking GaN transistors feature two gate structures that manage both negative and positive voltages, making them particularly useful for converters and rectifiers connected to the public grid, as noted by Fraunhofer IZM.
The circuit developed by the 'EnerConnect' team would be overly complex with traditional semiconductors, but GaN technology makes it feasible. This system, known as a buck-boost converter, can accommodate both higher and lower input voltages. The key lies in the bidirectional blocking transistors, which capitalize on the advantages of this design. Traditionally, active rectifiers in electric vehicles operate at high voltages, but the new circuit being investigated allows for lower voltage settings, which helps reduce switching losses.
Moreover, this circuit enables a reduction in converter stages. Typically, in a rectifier, the input voltage is first increased by two components and then reduced to match the required battery voltage. By employing bidirectional blocking GaN transistors, these two steps can be streamlined into a single converter stage, enhancing efficiency and lowering material costs.
As a result, the efficiency of the converter could potentially reach up to 99%, with a further increase in switching frequency also possible. Researchers have set an ambitious target of 300 kHz. "Aiming for a switching frequency of 300 kHz could boost power density to 15 kW per liter-an 800% increase over current market chargers," according to Fraunhofer IZM. This innovation could lead to the creation of a powerful onboard charger that is smaller than existing models.
In their announcement, Fraunhofer IZM emphasized the "significant advantages in power density and efficiency," suggesting that charging electric vehicles from standard household outlets could become much more effective. While this does not equate to the charging capacities of DC fast chargers, it implies the potential for compact 22 kW onboard chargers. Currently, most electric cars are equipped with three-phase 11 kW onboard chargers at 16 amps; for reasons of cost and space, many manufacturers do not offer 22 kW models. GaN transistors could address both space and cost challenges, making 22 kW onboard chargers more accessible.
Original News Website:
electrive.com, fraunhofer.de
Tags: #AC charging #wall box charger #home charging #DC fast chargers #22 kW onboard chargers #onboard charger #11 kW onboard chargers