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EV Charging - Electromechanical engineering for charging stations

  Knowledge

The development of high-performance charging infrastructure for e-mobility has created a whole new growth field for the use of high-grade electromechanical components, which include not only relays but also fuses, switches and thermal management components.

The automotive industry faces the challenge of focusing on the environment as one of the most important topics of our society and reducing emissions. The only way this is likely to be achievable is with electric motors. According to a study by McKinsey, it is estimated that as many as approximately 120 million electric vehicles will be registered for road use in China, the EU and the United States by 2030. Demand for charging energy will rise from around 20 billion kilowatt hours in 2020 to 280 billion kilowatt hours in 2030, for which around 40 million chargers will be needed, 15 million of them in Europe alone.

Leading automobile manufacturers have already announced an investment plan for the development of 400 charging stations in Europe. The current economic stimulus package of the German Federal Government also has a clear focus on electromobility. Around an additional € 2.5 billion is expected to be invested in developing charging station infrastructure.

For the imminent change and the development of a high-performance charging infrastructure, manufacturers such as BMW, VW, Mercedes and Audi are already adapting their production facilities and are preparing their workforces with training and certifications.

Relay Types Used in Charging Stations

A variety of electromechanical components are required both for electric cars and for charging stations. IEC 61851-1 defines the various types of charging stations. They are categorized on the basis of power supply criteria and electronic communication between the charging station and electric car. The choices of electromechanical components are dependent on the type of charging station in question.

Mode 1 and 2 charging stations that operate using alternating current have barely any electronics in them. In these cases, the vehicle's on-board charger (OBC) handles the charging cycle management.

Mode 3 charging stations require a relay to switch the AC current. As with other charging stations that use AC, the OBC limits charging performance here as well. The requirements placed upon the relay include 230V/400V (according to IEC 60664-1) and overvoltage category 4. This means that a distance of at least 3mm must be maintained between the contacts. Some suppliers offer appropriate products - Hongfa for example offers 35A/3.6mm (HF170F), 65A/3mm (HF176F) and 90A/3mm (HF167F) relays through Rutronik, while Omron supplies a 36A/3.2mm model (G6QE).

The trend is shifting towards DC fast-charge stations (Mode 4) as a solution for the problem of long charging times. The bulk of the electronics in these cases is located in the charging station, not in the vehicle. The vehicle's OBC is therefore circumvented. The charging process is handled directly by the charging station, which supplies the DC voltage. Mode 4 charging stations use a variety of relays:

The main relay covers a current range of 80 to 600A and is usually used to disconnect the battery. Models for this purpose are offered by Hongfa (HFE18V-300, HFE82V-250V) and Omron (G9TB).

The fast charge relay controls the fast charge process, with rated currents being between 32 and 600A. Suitable relays are available through Rutronik from Hongfa (HFE18V-600).

The HV pre-charge relay is used in the pre-charge circuit, for which a product such as Hongfa's HFE80V-20B can be used.

Relays for "auxiliary applications" (Figure 1) are mainly used for air conditioning systems, heating systems, DC-AC converters and other applications. They typically have a power rating of between 20 and 40A, and Hongfa once again has a suitable product in its portfolio for this in the form of the HFE18-200.

Relay Requirements

To qualify for automotive use, these relays must have compact dimensions and meet special technical specifications. Electric motors require very high power levels, which involves certain risks, so a reliable switch is essential here, which means that the relay contacts must not be at risk of oxidation. Suppliers have developed relays filled with gas (usually hydrogen) to prevent this, thus maintaining a lower contact resistance, avoiding power loss, and preventing relay failure. The relays from premium suppliers Omron and Hongfa meet these requirements and can be used in almost any application - whether in electric or hybrid vehicles, in 48V battery systems or charging stations.

Fuses

Because the operation of charging stations involves high voltages and currents, it is necessary to protect both people and the components. Surface-mounted, cartridge and high-voltage fuses are just a few of the components required here.

Depending on the type of charging station, other requirements may apply. Mode 1 to 3 charging stations are usually used in private households. Mode 4 fast charge stations on the other hand are installed in public spaces such as supermarkets and gas stations and require a high-current connection. Because they transform the AC voltage at the input to a DC voltage at the output, both circuits require fuses.

The fast-charge stations consist of extremely sensitive power semiconductors that can be adversely affected by interference such as voltage pulses and overcurrents. Special high-speed fuses such as the PSR series from Littelfuse (Figure 2) for the DC output have been developed precisely for this. They are extremely effective at limiting current and offer superb cycling capability. The JLLS series fuses from Littelfuse are ideal for AC input circuits. They also heavily limit current and prevent short-circuit currents faster than other mechanical safety mechanisms. This allows them to protect devices with components that are sensitive to overvoltages such as rectifiers. Both of these types are among the most compact fuses in the over 30A segment. Besides Littelfuse, Eaton also offers comparable models.

Efficient Thermal Management

The high power levels generate plenty of heat within the electronic components, and temperatures on the outside of charging stations can also get very high. This can have a severely negative impact on the function and life of the components, which is why efficient thermal management is essential. For this purpose, Rutronik offers a variety of solutions, including thermally conductive foils, heatsinks and fans from leading suppliers such as 3M, Delta Electronics, Fischer Elektronik, Assmann WSW, Jamicon, and Adda. The product and application specialists provide expert support in selecting suitable components.

Switches and Metal Keyboards

Suitable switches and metal keyboards for use in automotive applications enable ease of use of charging stations. A metal keyboard can for example be used to enter a PIN for authentication; microswitches can be used for example to start the charging process on the charger handle.

Because charging stations need to be able to withstand harsh environmental conditions such those as gas stations or supermarkets, they require a very robust metal keyboard that also works in the rain and in a variety of environmental temperatures. IP-Line from Knitter Switch is shipped with up to IP69K protection and IK08 impact resistance. The keyboards are also available with customized designs and offer a great deal of design scope.

To protect them against vandalism, they need vandal-proof pushbuttons with scratch-resistant actuators and a housing made of robust stainless steel. C&K metallic pushbuttons for example can resist extreme outdoor conditions and vandalism attempts with IP67 protection and IK10 impact resistance. The switches are also available with lighting in various colors and with labeling on the actuator.

This brief summary shows how electromechanical components in charging stations help to achieve e-mobility through everything from the control unit to the electric car connector to the charger plug - and in doing so, help to reduce CO2 emissions.

 

Find components at www.rutronik24.com.

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Figure 1: The HFE18-200 relay from Hongfa is perfect for auxiliary applications.
Figure 1: The HFE18-200 relay from Hongfa is perfect for auxiliary applications.