Compleo

The actual emergence of high-power chargers in Europe is a response to the increasing adoption of electric vehicles across the continent. High-power chargers (HPC), also known as ultra-fast chargers (UFC), provide EVs with a high amount of power in a short amount of time, allowing for longer driving ranges and faster recharging times. According to actual market expectations, a range of 200 km should be charged within 10 minutes soon. This results in an average power of 200 kW or more. The expansion of high-power charging infrastructure is crucial for encouraging the adoption of EVs and for making electric mobility a viable option for more people across Europe.

The European Union has set a target of having at least one million public charging points across the continent by 2025, including a significant number of high-power chargers. As of 2021, there are over 375,000 public charging points across Europe, and the number of high-power chargers has been steadily increasing [1]. According to the European Alternative Fuels Observatory [2], there are over 5,000 high-power chargers in Europe, with the majority located in countries such as Norway, Germany, France, the Netherlands, and the UK.

The CCS (Combined Charging System) standard for fast and high-power chargers is the most popular in Europe and North America. It provides typically up to 350 kW. However, higher power ratings are possible and will be supported by the second edition of the product standard IEC61851-23 scheduled for publication in Q2 2023.

 The most important part of these chargers in terms of size and cost is the power electronics subsystem. It is built typically by cascading several power converter modules typically ratedat 20 to 75 kW each to reach better serviceability, power scalability, and higher redundancy for high function availability.

To meet higher requirements of high efficiency and low footprint and thus the high-power density of these systems, new technologies like modern Silicon Carbide power semiconductors are required. Especially SiC-MOSFETs are very suitable for the design of charging power modules since they have lower onstate resistance (RDS_ON) and lower switching losses compared to traditional silicon-based MOSFETs, which translates to higher power conversion efficiency. Higher efficiency in combination with a higher temperature operation range of SiC-based semiconductors reduces the need for larger and more expensive cooling systems, which can help to decrease the overall system size and cost. Due to lower switching losses, higher switching frequencies can be achieved and contribute to smaller inductive and capacitive passive components. This can have also a positive impact on the system size and cost.

“SiC-semiconductor tech enables charging infrastructure with higher power density and improved efficiency, reducing noise generation and installation footprints for better sustainability in the electric transportation sector”

While silicon carbide MOSFET technology offers several advantages over traditional silicon based MOSFETs in power converter designs, some challenges must be considered during the design process. First, the higher switching speed combined with parasitic capacitances can lead to increased switching losses and electromagnetic interference (EMI) in the power converter circuit. Proper circuit layout and control techniques such as gate driver optimization and snubber circuits can help to mitigate these effects.

This adequate gate driver circuit is more complex and can cost more than conventional Si-based MOSFETs. In fact, SiC MOSFETs are more prone to failure due to their higher power density and operation temperature. Proper gate drive and protection circuitry must be implemented to ensure the reliability of the system. SiC MOSFETs are more sensitive to voltage spikes and overcurrent events, which means that the gate driver circuit must include adequate protection circuitry to prevent damage to the MOSFET. VDS protection and Miller- Clamp circuits are some recommended functions to increase the reliability and efficiency of the system.

Finally, SiC MOSFETs require specialized knowledge and design techniques to integrate into power converter designs. The selection of other components such as capacitors and inductors must also be carefully considered to ensure compatibility with SiC MOSFETs.

Thanks to SiC-semiconductor technology, the described trend towards higher power density will enable better integration of charging infrastructure not only on long-distance inter-city connections like highways but also in urban areas, since the footprint of the installations decreases and the extra gain of efficiency will reduce their noise generation, due to lower cooling requirements.