Why EV chargers need auxiliary power busbars

Complex demands placed on auxiliary power supplies

DC charging of electric vehicles is an emerging market with special technical requirements. While the development of mains power conversion technology is well advanced, there is a need for low power AC/DC and DC/DC auxiliary power supplies.

Background

The number of installed chargers for electric cars is growing exponentially. At the same time, the complexity of the chargers in use is high, ranging from a slow, simple, single-phase household AC source for on-board charging to ultra-fast DC chargers of 800V or more, powered by a three-phase AC supply and equipped with multiple processors and interfaces. In addition, for each DC charger, a series of low-power auxiliary busbars should be used.

Figure 1: The chargers are highly complex devices, and each DC charger requires are series of auxiliary power busbars.

Although a multi-kW mains power supply can also generate direct current with low power – e.g. from a winding of the PFC inductor – there are a number of reasons why this is rarely useful:

• Efficiency: The mains power supply of the DC charger, when not under load, causes considerable losses. At their typical operating values, low-power AC/DC power supplies offer high efficiency.

• Safety: An independent supply via an auxiliary busbar makes switching the mains power supply on and off much safer and more predictable.

• Reducing ground loops and EMC problems: Separate low-power AC/DC power supplies allow isolated DC return paths for different parts of the system.

• Regulation and noise level: Both isolated and non-isolated DC/DC power supplies can also be connected downstream of the AC/DC auxiliary power supplies to generate any necessary “point-of-load” voltages to meet specific control and noise level requirements.

The challenge

AC/DC and DC/DC auxiliary power supplies in DC chargers have to be in accord with special environmental requirements. A long service life and high reliability coupled with industrial quality parts are basic requirements. Moreover, certain standards still have to be met:

• Over-voltage protection: Among its stipulations, EN 61851-23 “Electric vehicle conductive charging system – DC electric vehicle charging station” specifies that the power supply of an EV charging station must conform to over-voltage category (OVC) III or IV. This means that even most industrial AC/DC power supplies are unsuitable – as a rule, these only meet the requirements of OVC II for mains installations after they have been fitted with over-voltage protection.
Furthermore, the safety margins required in a unit for an overvoltage class correlate with the geographical altitude. Up to 2000m, no correction is needed. With increasing altitude, however, the safety margins needs to be increased more and more.

• Environmental conditions: Damp, dirty, or dusty environments are typically found in garages and on outdoor parking areas. To avoid malfunctions in such environmental conditions, the electronics need to be encapsulated or coated, or need much higher creepage distances. EN 61851-23 lays out the degree of contamination for which the electronics must be designed. Grade 3 specifies outdoor and industrial use, while Grade 2 specifies indoor use.
The temperature range in which the electronics are used plays a crucial role. Charging station electronics in outdoor installations have to be able to withstand temperatures from below freezing up to +60°C in full sunlight. Industrial AC/DC power supplies are typically designed for use in ambient temperatures from -40°C to + 85°C, which is sufficient for this purpose.

The solution

RECOM offers a range of standard products that meet the complex requirements of DC chargers for low-power electric vehicles and which are also suitable for many other applications.

Among their standard products are the encapsulated miniature modules in the RAC series, rated from 3W to 40W, which are suitable for environments with a high level of contamination. In addition to the “standard” input range of 85-264VAC, some variants are designed for 305VAC for 277VAC nominal. The RAC05-K/480 is even designed for an input of up to 528VAC (Figure 2). The operating temperature range of all modules is from -40°C to +80°C, and all are available with OVC III approval either as standard or optionally. The safety certification of all these RECOM modules is comprehensive, with IEC/EN 62368-1 being the minimum – some even meet IEC/EN 61558 or EN 60335-1 for domestic use or even IEC/EN 60601-1 for medical applications.

Figure 2: RECOM RAC05-K/480 with 528VAC input and OVC III rating

What’s more, the RECOM range encompasses a broad selection of DC/DC power supplies suitable for gate drive power for the mains power supply, and for isolated communications interfaces, isolated auxiliary busbars and non-isolated point-of-load power supplies. All of these power supplies are designed for use in demanding environments.

At Schukat

Schukat offers power supplies from RECOM and other manufacturers. Schukat stocks around 6000 different types of power supplies and DC/DC converters in production quantities at its automated central warehouse in Monheim am Rhein, Germany.

As a distributor, we provide fast, competent support with direct contact persons in-house, and also have an expert field service team for on-site problem solving. Customers benefit from rapid processing of inquiries, availability of data sheets and samples, and variable delivery quantities – from samples to series production.
Our technical sales team is here to help when selecting suitable power supply products as well as for any customer-specific questions relating to power supplies