Friwo : DC/DC converter for electromobility

12. April 2017

Electric bicycles have been enjoying tremendous popularity for quite some time, e-scooters are also increasingly roaming the streets. In addition to the supply voltage for their drive, these vehicles require a lower voltage of 12 V for indicators and headlights, which is typically buffered by a corresponding lead acid battery. A new FRIWO DC/DC converter ensures the supply of the additional battery from a 48 V traction battery.

Currently the subject of electromobility is much talked about. This is attributable to the limited fossil fuels, particularly oil, and to CO2 gases generated during combustion, which contribute to global warming and therefore to environmental pollution (for example soot particles, nitrogen oxides, etc.).

Electric cars are still a niche market. There are only a few models and manufacturers worldwide. One reason for this situation is certainly owed to the increased comfort demand - including luxury. This includes, for instance, extras like air conditioning, seat heating or heated front and rear windshields which usually can be found in conventional cars.

Unlike electric cars, however, electric bicycles have become rapidly popular. The annual sales figures continue to rise: according to the ZIV industry association, 605,000 e-bikes were sold in Germany in 2016. This means that the overall market share increased from 12.5 percent in 2015 to 15 percent in 2016. If children's bicycles and racing bikes are ignored, the share is even significantly higher. According to ZIV, a total of three million e-bikes roam Germany's cycle paths since the beginning of 2017*. All of this, of course, in a comfortable way to ensure a faster and easier mobility.

E-scooters, also known as electric mopeds or electric light-weight bikes, are an extension of this product range towards more mileage and speed. Having enjoyed increasing popularity in Asia for quite some time, these vehicles are coming on strong in our country. With the improvement of the required charging infrastructure, the numbers of eco-friendly electric scooters will also increase on our streets. Especially in big cities, the quiet two-wheelers are more frequently spotted, private owners and delivery services are switching over to this eco-friendly alternative. In addition, e-scooter rentals and sharing are emerging: Apart from Berlin, Hamburg and Munich many big cities in North Rhine-Westphalia belong to the driving forces.

E-scooters typically extract the energy required for their operation from a 13-cell rechargeable battery. 13 cells with a nominal voltage of 46.8 V still fall under the so-called safety extra low voltage, but already provide a voltage level at which the resulting currents can be controlled by a predetermined power. This cell number is currently becoming industry standard. As far as e-scooters are concerned, a 12 V level for indicators and headlights is also required. These 12 V are, as practiced today, buffered by a 12 V battery. This means that the 12 V battery needs to be supplied by the 48 V traction battery. FRIWO has therefore developed a new DC/DC converter which copes with this task and which offers a variety of advantages:

1. In addition to the nominal charging power of 150 W (13,8 V x 11 A charging current), the converter is capable of supplying a short-term peak current of 13.2 A (+20 % boost), which comes in handy if the battery is deeply discharged, or in case of short-term loading demands.
2. The converter's efficiency reads more than 95 %. The high power density allows a very compact design. The compact design is also owed to the converter's cooling system which is achieved by natural convection. The converter therefore does neither require a fan, nor an external metal fixture for the purpose of cooling by increased surface. The high efficiency serves as basis for a long shelf-life and high reliability.
3. Operating temperatures range from -20°C to 80°C. This allows the converter to work both in deepest winter as well as in the hottest summer - the electric vehicle is always ready for use. From a temperature of 60°C upwards the converter automatically reduces the output power (so-called derating) with natural convection.
4. The potted converter has IP67 protection and is robust against typical automotive requirements: temperature changes, salt spray, vibrations or shocks will no longer be a problem.
5. A significant advantage is also constituted by the electrical characteristics: in addition to the wide DC input voltage of 30 - 60 V the converter has a very accurate output voltage regulation with <1 % deviation. A low reverse current of <100 µA from the 12 V battery also prevents unwanted discharges.
6. The converter comes with a µController for numerous functions. This includes, for example, a self-test after starting, the adjustable (during production) output voltage and current limit, an output curve optimized for parallel operation, temperature monitoring of the converter with derating function, and the fulfillment of short-term peak current requirements until derating starts.
7. Electromagnetic compatibility (EMC) includes both the interference emission and the interference immunity of the converter against external interference. The converter complies with the automotive standards for both requirements: low noise emission (especially in the FM band) and high immunity to interference and overvoltage pulses.
8. A communication interface is also provided: securely connected to the 48 V and 12 V electrical system the converter is activated by an 'enable' signal and acknowledges the correct operation with a 'power good' signal.
9. Redundant switches have also been installed for safety reasons. They prevent short-circuits between the input and output electrical system which may be caused by a broken line transistor.
10. Further protective functions ensure the highest level of safety: The converter is permanently short-circuit proof and has both overvoltage and over temperature protection. In addition, the soft start after switching on and the mechanical polarity protection for input and output plugs increase the safety. An additional electronic polarity protection can also be provided.

With the new DC/DC converter FRIWO has engineered an ideal component for Light Electric Vehicles (LEV) which optimally completes the existing product portfolio with battery chargers and battery packs and which drives FRIWO's integration as system supplier for tomorrow's market of electromobility.
https://www.wired.de/collection/tech/e-roller-startups-erobern-deutschlands-staedte