Bidirectional On-Board Chargers: Smaller, Sooner, Cheaper

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On-board chargers are the nice equalizers for electrical automobile charging — and generally is a game-changer for the way forward for e-mobility. Fraunhofer IZM has managed to deliver collectively a few of the most progressive concepts in energy electronics to pave the way in which for a brand new technology of on-board chargers. Twice the efficiency at half the scale, bidirectional capabilities, and effectively machine-made: The ensuing on-board charger is the economical ticket to the quick lane into the long run.

Drivers fortunate sufficient to discover a excessive energy charging (HPC) or different fast-charging stations can count on their electrical automobiles to be charged and able to go in round 15 to half-hour. That feat is made doable by the large energy packed into these chargers, with some varieties delivering as much as 350 kW. And that energy is delivered in DC kind, simply as electrical automobile batteries want. This implies charging the batteries instantly with out want for an on-board charger.

Not so with AC chargers, that are by far the extra frequent kind. They vary from the frequent family socket present in most garages, providing as much as 3 kW on a single part of AC present. Extra promisingly, three-phase AC present from common public e-vehicle charging factors or home wallbox-type chargers can cost batteries with as much as 22 kW, permitting the batteries of many automobiles to be crammed utterly in about 4 hours. Nevertheless, lots of the e-vehicles at the moment in use are designed to absorb a most of 11 kW – a bottleneck created by the on-board charger (or OBC) they’re fitted with. Present OBCs are usually constituted of a variety of separate elements, together with massive coils, which can be usually made and assembled manually and take up a number of area within the automobile. Many electrical automobile makers provide an elective improve from 11 to 22 kW, both by becoming a second OBC or utilizing a bigger module. Each choices come at a premium, each in value and area, and most OBC work solely unidirectionally, that’s, just for charging the automobile battery. They may not feed saved energy again into the grid or enable parked electrical automobiles to behave as a sort of buffer for home solar energy programs. The promise of electrical automobiles coming to the rescue of the inexperienced power transition as a distributed power storage community stays a pipe dream with the previous know-how.

Sinus amplitude converter with gallium nitride semiconductors for speeds above 1 MHz

Breaking via this technological barrier meant that Fraunhofer IZM needed to develop not one, however a number of new elements and discover a method to match them collectively in a tiny bundle. One key element is a sinus amplitude converter (SAC), a resonant high-frequency transformer. Its main mission is to make sure that the automobile battery is galvanically remoted from the general public grid, as a result of the parasitic earth currents created by the on-board capacitors may trigger a floor fault within the circuit and cease the system from working. The progressive a part of the brand new SAC is the gallium nitride (GaN) switches used within the Fraunhofer IZM design – novel, high-performance semiconductors with a large bandgap that make it doable to modify the converters at a frequency of 1.3 MHz or 1.3 million instances per second. Oleg Zeiter, who oversaw Fraunhofer IZM’s work on the brand new OBC, explains: “These excessive frequencies imply that we will completely rethink how we design the module.” This has a direct impact on one other important element: the PFC choke.

PFC inductor – Flat coils, machine-made

An OBC has one different key element, referred to as the Energy Issue Correction (PFC). It acts because the bridge with the general public grid and provides the incoming alternating present a secure sinus form at – relying on the native grid – 50 or 60 Hz. To take action, it makes use of chokes, a really cumbersome and really pricey half within the standard OBC designs. Fraunhofer IZM now makes use of a flat PFC inductor designed in circuit board kind that has 4 magnetically coupled coils on a shared ferrite core. The PFC choke is just not solely a lot smaller; it can be made by machine, as a substitute of by hand. The planar design signifies that the choke can solely generate decrease inductivity, however that is no difficulty for the PFCs fitted with SiC switches and dealing at 140 KHz. “The low inductivity doesn’t pose an issue for us, as a result of we ramped up the switching frequency,” Oleg Zeiter explains. “As a result of we solely ever change on the present for a particularly temporary second in time, it by no means reaches excessive amperage, even at low inductivity – all because of the short switching.”

The good packaging and interconnection methods employed by Fraunhofer IZM lastly allowed the Institute to create an OBC that may be a mere three cubic decimeters in quantity: half the scale of standard OBC, however with double the charging capability at 22 kW. “In essence, we’re simply working with one large circuit board. Our packaging options imply that we will have a machine match every part we’d like on this board,” Oleg Zeiter says. In observe, this implies a significant discount in manufacturing value.

However these will not be the one benefits of the brand new OBCs: The module can accommodate 400 and 800 V batteries and works at greater than 97 % effectivity. And the brand new OBC can let currents move in each instructions, from the grid to the battery and again once more. Which means one of many fundamental questions of the power transition has been resolved, at the least from a technical standpoint, a feat made doable with assist from the ECSEL JU initiative (Digital Parts and Techniques for European Management Joint Endeavor) as a part of the Horizon 2020 analysis and innovation program.

Anyone on this system and its mixture of various technical methods can see it up shut from 11 to 13 June at Nuremberg’s PCIM Europe expo, the worldwide expo for energy electronics. The Fraunhofer IZM sales space (corridor 5, sales space 300) will host the premiere for the brand new on-board charger.

By Christoph Hein. Courtesy of Fraunhofer IZM.