The Formula Student Electric (FSE) racing car developed at the University of Munich has six highly isolated RECOM DC/DC converters on each wheel supplying the power electronics.
No doubt about it. Cars have changed the world in the past hundred years. Even so, the trend towards even faster and bigger models seems to have been bucked. Climate change and diminishing resources have forced us to rethink. Electron power has replaced horsepower in defining a car’s performance, with fascinating applications emerging for modular converters.
While there seems to be growing interests in Electric Cars globally in the recent years with political and environmental activists campaigning for the same, adoption for electric cars still seems to be sluggish. So what are the factors that could be affecting this trend?
Some Possible Drawbacks
- Range and lack of charging stations: The lithium-ion batteries available barely have enough capacity to cater for long driving hours. Apart from that, finding quick-charging stations are still very scarce in many areas. And once found, it’s still almost an hour’s wait for the battery to charge up enough for a couple of hours drive. This means that pure Electric Cars only make sense as second cars for short distance driving.
- Electric Cars are still too expensive: Electric Cars are still too expensive for the mass market. The savings might pay in the long run given the lower maintenance costs of Electric Cars, but the upfront cost is still considered pretty hefty as compared to a regular car.
Limited battery life: Electric Cars save on maintenance costs such as oil changes, but the heavy cost of replacing a worn-out battery looms large after a few years.
- E-mobility is not as clean as its reputation: Even without an exhaust pipe, Electric Cars are not nearly as clean as their reputation. The raw materials used in lithium-ion batteries include lithium, cobalt and nickel, which are mined in countries where environmental protection is not high on the priority list. Apart from that, manufacturing emissions average more than a hundred kilos of carbon dioxide per kilowatt-hour of battery capacity. In addition, the electrical power needed to charge the battery is only free of emissions if it comes from renewable sources.
- The raw materials are not available in unlimited quantities: Nobody knows how long lithium deposits and other resources will last in amounts high enough to meet the needs of global e-mobility. As resources dwindle, the price of batteries may well rise rather than fall, especially as the battery will have to be replaced at least once over the lifetime of the Electric Cars. The raw materials can to some extent be recovered by recycling, but this process is time-consuming and expensive.
With this in mind, enthusiasm for e-mobility is unsurprisingly lukewarm. It’s almost as if the time hasn’t quite come for battery-powered motoring – especially considering that a battery with 400km range weighs in at 600 kilos. This weight needs to be moved along with the car, decreasing efficiency. It comes as little consolation that electric motors are heavier than conventional car engines – even if some of the power can be recovered during braking.
How voltage transformers come into the picture
Charging circuitry is required to convert AC power from the grid into high DC voltage while monitoring and controlling the charging process before an Electric Car can set off with a fully charged battery. A conventional 230V socket is enough to charge a small Electric Car in the garage overnight. The car comes with its own charging circuitry. The charging process will take hours at the maximum 2.3kW power available from a domestic power outlet.
Public and fast-charging stations are quicker as they pull more than 100kW and take an hour or so to charge up an 85kWh battery. Ultra-high-power stations still under development can handle up to 400kW. This would speed up the charging process to around a quarter of an hour, which would easily fit in with quick breaks planned in every few hundred kilometres.
All major charging stations use DC voltage to charge up Electric Car batteries. Voltages of 400V are currently standard, but this could rise to 800V sometime in the future. Voltages of this scale are deadly on contact even if DC voltage is thought of as safe in a home environment. Demands on the reliability of the whole system are correspondingly high.
This needs mechanically robust plug connections as well as a reliable electronic safety system. To this end, the battery management system in the car keeps constant communication with the charging station. The power only flows with the charger plug securely seated in the charging socket and the battery charger transmitting a constant “ok” signal. The charging station instantly disconnects on any interruption to the signal.
The RECOM RAC05-xxSK/480 was developed for this monitoring task (Fig. 2). The AC/DC converter operates at input voltages of up to 528V AC, and therefore easily operates between two phases in the three-phase system. Isolated for voltages of up to 4kV, the 5W converter converts three-phase power into low DC voltages of 5 or 12V DC for the monitoring electronics. The AC/DC converter’s auxiliary power powers the handshaking system that only allows power to flow if everything else is in good order.
Not only charging stations need thorough monitoring; the battery itself requires constant observation. Advanced lithium-ion batteries are usually arranged into several modules. Current, voltage and temperature in each module need to be monitored separately to ensure a charging process that preserves the battery. It has to be possible to switch off individual modules if they fail while continuing to supply power to the healthy modules. A complex electronic system is vital in battery life maximisation and failure protection for individual cells.
RECOM has already developed a series of 1W DC/DC converters used for battery management in Electric Cars. Each battery module needs its own DC/DC converter to isolate monitoring electronics equipment operating at various floating voltages from the CAN bus. RECOM converters are isolated for voltages of 5.2kV DC and hi-pot-tested.
Highly isolated DC/DC converters are also used for controlling power semiconductors in charging stations. This involves using IGBT, SiC or Si MOSFETs or GaN FETs controlled by gate drivers, which require a positive and negative voltage each to accelerate the switching process and avoid misfires.
The power switches have high floating voltages, so the driver’s voltage supply needs very effective isolation. RECOM has developed dual “reinforced” isolated DC/DC converters with output voltages of +15V/-9V (IGBT), +15V/-3V and +20V/5V (SiC) and +6V/+9V (GaN) for the purpose. These converters have especially low coupling capacities to ensure long system service life.
Motor racing generates innovation
Motor racing provides an effective general barometer of technological change. Additional electric power plays an essential role in winning at formula racing. Formula E has been growing from strength to strength and runs on electricity. The race can be completed on one battery charge now compared to years ago, when the car had to be changed mid-race.
Universities are also working hard on the future. For example, students at the University of Munich were working together with municHMotorsport on an electrically powered racing car to run in the Formula Student Electric (FSE) race. The four three-phase motors in the wheel hubs were equipped with a total of twenty-four isolated DC/DC converters from the RECOM RxxP2xx family to power the control electronics. The vehicle they developed runs at 174 bhp and goes from 0 to 100 km/h in less than two seconds.
Researchers across the world are working hard on improving e-mobility technology – not least in China. Whether or not lithium-ion batteries will be the last word remains to be seen. Researchers at the Institute for Energy and Climate Research see a lot of potential in developing a new type of solid-state battery. All the components are manufactured from phosphate compounds. There doesn’t seem to be any lack of resources for these. No fluids are used, so they should be safer and more durable than lithium-ion batteries.
Hydrogen-powered fuel cells are also considered promising. The Friedrich Alexander University of Erlangen is researching safe “fuels” with hydrogen organically bound in oil. These liquid organic hydrogen carriers (LOHCs) are neither flammable nor toxic and can be used the same way as conventional fuel in normal fuel tanks. Cars would need around the same amount of LOHC fuel as normal car fuel to cover a distance of 600–800 km. The existing service station network could also be used for filling up with LOHC fuel.
Even so, the drive will definitely be electric with electronic control, monitoring and communication. This will require a variety of innovative voltage converters – one reason for RECOM to focus specifically on e-mobility.