Renault, CEA develop bidirectional on-board charging system for BEVs

Technology News |
By Christoph Hammerschmidt

In a joint development effort with the French Commissariat for Atomic Energy and Alternative Energies CEA, the Renault Group devised a bidirectional charging system for electric vehicles. The specifications were ambitious.

The planned compact and highly efficient system should reduce energy losses during charging by a 30%. This not only reduces waste heat, but also ensures significantly shorter charging times. It will also be vehicle-to-grid (V2G) capable, allowing energy from the battery to be fed back into the grid to optimise grid operation and compensate for fluctuations in renewable energy. The charger is expected to be used in Renault’s production models by the end of the decade.

At the heart of the bidirectional charger is a new electronic power converter architecture that is integrated directly into the vehicle’s charger. The converter is the result of almost three years of research and combines eleven joint patents. It is made of innovative materials and is more compact than previous systems. The new architecture, based on wide bandgap semiconductor materials such as gallium nitride (GaN) or silicon carbide (SiC), makes it possible to reduce energy losses during voltage conversion by 30 % and to reduce heat generation by the same amount. This is associated with a further advantage: The effort required to cool the system can be significantly reduced.

Less volume, more power

In addition, by optimising the active and passive components (capacitors and wound inductive components), the joint development teams were able to reduce the volume and cost of the charger. Among other things, they were able to make the voltage converter more compact by using ferrite materials suitable for high frequencies. The innovative manufacturing process of powder injection moulding also contributes to the miniaturisation of the system.

This new converter architecture enables a charging power of up to 22 kW in three-phase operation, which enables faster vehicle charging while ensuring battery durability. In addition, the device can be operated bidirectionally, so that the energy stored in the battery can be fed back into the grid or used to meet the energy needs of an autonomous home. Which however requires that the house is already equipped with a bidirectional electric meter system. The solution is compatible with the electromagnetic compatibility (EMC) standards of the grids and the vehicle.

Jean-François Salessy, Vice-President Advanced Engineering at Renault Group, says: “The joint project with the CEA has exceeded our expectations, confirming that we can achieve the expected performance in terms of efficiency and compactness. It opens up good prospects for power electronics, which is a real challenge in the electric vehicle, in order to make the best use of the batteries’ capacities. With bidirectional charging, the vehicle supports the electricity grid and allows the end user to reduce energy costs.”

According to François Legalland, CEO of CEA-Liten (Laboratoire d’innovation pour les technologies des énergies nouvelles et les nanomatériaux), the use of innovative materials with joint Renault Group and CEA patents for the charger enabled the production of a special transformer. This is a key component in that it allows power beyond the current state of the art in a smaller volume.


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