Session: 04-08: Emerging Integrated System Applications

Paper Number: 90430

90430 - Charging Plug With Smart Clamp Contacts for Fast Charging of Electric Cars 

Charging electric cars at fast-charging stations is nowadays limited, among other things, by the maximum electrical power that can be transmitted at the contact points between the CCS plug and the vehicle input. The Combined Charging System (CCS) is based on open and universal standards for electric vehicles. The CCS combines single-phase and fast three-phase charging using alternating current with a maximum of 43 kW, as well as direct-current charging at a maximum of 200 kW and, in the future, up to 350 kW – all in one system. The charging stations available on the market today can only offer a maximum of 150 kW.

In order to reduce the charging time, the electrical contact resistance in the DC contacts of the CCS plug, must be minimized. Since the contact surface of such connector is limited, the contact forces between the charging plug and the vehicle input must be increased. However, if the contact forces are too high, the plug can no longer be inserted by hand. For this reason, today lower contact forces are accepted along with a strong heating of the connection. In order to be able to transmit high electrical power, today's systems include active cooling of the contacts. In addition to the enormous technical effort, this solution also reduces the efficiency of the charging system.

A potential solution for this problem is to temporarily increase the clamping or contact force of the connector during the charging process using shape memory alloy (SMA) actuators. SMAs provide a thermosensitive material that can generate large mechanical stresses and strains during phase transformation. This effect can be used to actively increase the contact normal force when the contact areas in the charging plug are subjected to high thermal loads.  The objective of the novel working principle is to achieve a higher current-carrying capability of CCS plugs without active cooling. A significant simplification and compactness of the system compared to liquid-cooled plug-inlet systems can thus be achieved.

The integration of SMA clamping mechanisms enables an easy increase of the clamping force between the socket of the plug and the pin of the vehicle connector during the charging process. The force to insert the plug can even be reduced, thus also positively affecting the ease of use. This technical innovation not only reduces the complexity of the fast-charging stations by eliminating the cooling system, but also significantly reduces the investment and operating costs. This is of enormous importance for the further growth of the fast-charging infrastructure. In addition to the technical and economic factors mentioned, the efficiency of the charging process also increases due to the lower heat losses at the contact points, which even have to be taken into account twice in actively cooled systems (generation and dissipation of the heat loss). The SMA-based clamping system thus represents an enormous improvement over the status quo in terms of economic efficiency and sustainability.

This paper presents different designs of SMA-based clamping systems and describes their development process. Furthermore, the results of the first evaluation tests are shown and discussed.

Presenting Author: Sven Langbein Adolf Edelhoff Gmbh & Co.