Column: Electric Vehicles
Exploring the DC fast charging solutions Expanding the DC network of charging stations will help, but it’s neither the most expeditious nor most cost effective. There are two ways to achieve this:
1. Adding 800V stations: Installing new DC fast-charging stations with wide-voltage capability (250-920V) is one solution, but it requires considerable time and money investment. Today there are approximately 1000 800V charging stations in Europe and the US – that’s only about 2% of all available DC charging stations. To address the growth of 800V EVs, that network needs hundreds more stations – a long and cost- prohibitive process.
2. Upgrading the 400V stations: Another approach is to upgrade the existing 400V stations to support 800V; this, however, also brings challenges. Charging at ultra-high- power rates (>150kW) is not always available nor possible (temperature, battery degradation, etc.). Also, charging times would be slower than required for 800V.
Onboard charging In contrast to spending on the charging network, vehicle onboard conversion solutions could be a better approach. It could be adopted much more quickly and with no capital investment in the charging infrastructure. “Battery virtualisation” is the answer
here. The charger “sees” a 400V battery on one side of the onboard charger, even if an 800V battery is connected to the other side. This approach starts from the battery voltage and adapts it to the voltage range acceptable by the charging station; see Figure 1. Vicor high-density, high-power
modules can be used here, without adding size, weight and design complexity. Our NBM bidirectional modules convert tens of kilowatts of power, reaching 550kW/litre and
18 December/January 2023
www.electronicsworld.com Figure 2: Vicor NBM bidirectional modules
This imbalance between 400V and 800V charging stations is fast becoming a significant
problem as OEMs begin rolling out new 800V vehicles: the public infrastructure to charge them is inadequate
130kW/kg in power density, and use power converters that are at least 50% smaller and lighter than discrete solutions. Our proprietary Sine Amplitude
Converter (SAC) topology ensures soft switching on the primary and secondary sides, reaching 99% efficiency, and allowing for simple EMC design and flexible cooling management. Connecting a battery to one side of an NBM module will immediately virtualise a battery on the other side, dividing or multiplying the voltage or current by a constant factor. Ultimately, NBM modules extend the voltage range of charging stations (250-460V to 500-920V), thus increasing the number of overall available charging points and making an EV compatible with any DC charging station. In addition, the NBMs also easily
integrate with the traction battery to deliver higher efficiency for low RPM driving. For example, city driving requires lower RPMs and the 800V traction inverter efficiency falls drastically by over 15%. The NBM can be used in this ancillary manner to supply the inverter with half the battery voltage, halving switching losses and extending driving range.
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