The year 1996 was a significant one in electric vehicle history. That was the year the General Motors EV1 hit the market. The EV1 was the first mass-produced and purpose-designed electric vehicle of the modern era from a major automaker and the first GM car designed from the ground up to be an electric vehicle.
Those first EV1s used a lead-acid battery with a capacity of 16.5–18.7 kWh and an output voltage of 312V; Gen 2 vehicles used a nickel–metal hydride (NiMH) battery with 26.4 kWh capacity. Sadly, the market wasn’t ready for the EV1, and its production ended in 1999.
battery chemistry
Fast forward twenty years, and although the battery chemistry is overwhelmingly based on lithium-ion (LI-ion), other changes in the battery pack have been modest.
The operating voltage has crept up to around 400V; the capacity can be as low as 17kWh for mini cars, although high-end batteries for performance vehicles can exceed 100kWh.
EV capacities
Porsche’s Taycan that ditch the 400V battery in favor of an 800V system
Apart from any breakthroughs in battery design, EV capacities are expected to continue their incremental increase, although big changes are on the way in operating voltage.
Say hello to a new generation of EVs, such as Porsche’s Taycan shown in Figure 1, that ditch the 400V battery in favor of an 800V system.
How a Higher Voltage Solves EV Challenges
Why the push to a higher voltage? Two of the main challenges for EV adoption are limited range and long recharge times. Ultra-fast charging can help to mitigate both concerns, but a current-generation DC fast charger for a 400V EV can only supply 50–60kW power output, running at 480+ volts and 100+ amps.
This can fully charge an EV with a 100-mile range battery in slightly more than 30 minutes.
charging rate
A safe operating zone in a Li-ion battery can decrease performance; if it gets too high, it can cause an exothermic reaction
For 400V battery EVs, the charging rate is limited by the practical cable size required to carry the charging current. Increasing the charging current translates into extra heat generation in the battery.
An internal temperature that exceeds the safe operating zone in a Li-ion battery can decrease performance; if it gets too high, it can cause an exothermic reaction, thermal runaway, and a fire.
driving range
A higher voltage allows a lower current to be used when charging the battery, which reduces overheating and allows better power retention. This contributes towards a greater driving range.
It also allows for weight reduction, as less copper is needed in the vehicle's electric system. This allows for smaller motors, freeing up space in the vehicle for additional battery capacity to increase the range.
Reliability and Safety Considerations for 800V
DC voltages at this level are deadly on contact even if lower DC voltages are usually considered safe
New generations of DC fast chargers running at 800V can produce 150–350 kW of power. However, the design of an 800V EV requires careful new considerations for all electrical systems. DC voltages at this level are deadly on contact even if lower DC voltages are usually considered safe.
As a result, system reliability requirements are high across the board. A high-power three-phase EV charger needs mechanically robust plug connections as well as a reliable electronic safety system.
battery management system
The battery management system in the car maintains 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 from any interruption to the signal.
power infrastructure
As Figure 1 illustrates, a high-power EV charger, regardless of output voltage, needs multiple low-power internal power supplies to create a fault-tolerant, safe, and reliable power infrastructure. These include:
- AC/DC converters for auxiliary power, safety interlocks, and control circuits with overvoltage category 3 (OVCIII) protection according to the IEC62477-1 safety standard.
- Isolated DC/DC converters for gate drivers, sensors, and input isolation.
- Non-isolated DC/DC converters for the internal distributed power architecture and dual-rail analog circuits.
Advanced Li-ion batteries
It has to be possible to switch off individual modules if they fail while continuing to supply power
Not only do charging stations need thorough monitoring; but the EV battery itself requires constant observation. Advanced Li-ion batteries are usually arranged into several modules. The current, voltage, and temperature in each module need to be monitored separately to ensure that the charging process keeps within the SOA of the battery.
It has to be possible to switch off individual modules if they fail while continuing to supply power to the healthy modules.
complex electronic system
A complex electronic system is vital in battery life maximization and failure protection for individual cells.
Even as EVs with 800V batteries start to appear, most chargers will still use 400V, so the new 800V EVs are capable of using either a 400V or an 800V charger. Other 400V models have been designed for an easy transition to 800V operation when the market dictates.
EV Charging Solutions
RECOM’s RAC05-xxSK/480 was developed for the monitoring task in the charger
How can RECOM help? It provides a range of low-power AC/DC modules, DC/DC converters, and switching regulators that match the battery charging application requirements for auxiliary supplies in a fast DC charger.
For example, RECOM’s RAC05-xxSK/480 was developed for the monitoring task in the charger.
three-phase system
The AC/DC converter operates at input voltages of up to 528V AC, and so 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 allows power to flow only if everything else is in good order.
wireless interfaces
RECOM also offers a non-isolated 3.8VDC/3A supply for the wireless interfaces: the RPL-3.0, a tiny 3mm2 buck converter with an integrated inductor that features adjustable output and full protection (SCP, OLP, OVP, OTP, UVLO).
RECOM’s subsidiary company, Power Control Systems (PCS), can supply high-reliability custom battery chargers, conditioners, and bidirectional inverters based on proven platform designs from three-phase AC supplies with power ratings of up to 30kW or even higher with paralleled units.