To ensure a successful transition to electric mobility, the widespread availability of efficient and reliable EV charging stations is critical. Whether it is residential charging solutions or high-speed chargers, these stations are vital for providing the power needed to keep EVs on the road, alleviating range anxiety, and ensuring convenience for everyday use.
At the heart of these systems are the semiconductors which enable the conversion, distribution, and management of electric power within the EV charger. Let’s explore the types of charging systems and the role that semiconductors play in this electric ecosystem. Of course, there are numerous different systems, but primarily they can be split into either AC (Alternating Current) or DC (Direct Current) solutions and both are essential for a comprehensive network. AC charging relies on the vehicle’s onboard charger to convert AC to DC, making it ideal for routine overnight charging. In contrast, DC fast charging bypasses the onboard charger (OBC) to deliver rapid power directly to the battery, allowing for quick recharges at public stations, crucial for long trips and fast top-ups.
AC charging: simple and inexpensive but slow
AC EV wallboxes are relatively simple designs that supply single or 3-phase AC power to the vehicle, where the onboard charger (OBC) converts it into DC before reaching the battery. The speed of charging is determined by the onboard charger’s capacity (typically between 3-22 kW). Depending on the charger’s power rating and the type of vehicle, a full battery charge usually takes 8-12 hours which makes it ideal for use at home or workstations. AC chargers typically consist of power supply units, safety mechanisms, and communication systems that interact with the vehicle to ensure safe and optimized charging.
One of the most significant trends in AC charging is the integration with smart home energy management systems and residential battery energy storage systems (BESS). As more homeowners install solar panels and energy storage solutions, there is a growing opportunity to optimize EV charging based on renewable energy availability. For example, a home equipped with solar panels can use excess solar energy generated during the day to charge an EV, making the charging process both eco-friendly and cost-effective. Smart chargers can also respond to grid signals, adjusting charging times to take advantage of off-peak electricity rates or to reduce strain on the grid. This trend not only benefits the homeowner but also contributes to a more stable and efficient energy ecosystem.
.svg "Block diagram of an AC EV charging station")
DC charging: Fast and efficient, but complex and high-power
Unlike AC chargers, DC EV charging stations supply DC power (15-350 kW) directly to the vehicle’s battery and are designed for high-speed energy delivery. That makes them crucial for public charging infrastructure, particularly along highways and in urban areas. Depending on the charger and the vehicle, it’s possible to add hundreds of miles of range in under 30 minutes. To efficiently handle large amounts of energy, the power electronics in a DC charging station are highly complex, integrating advanced components such as power modules, sensors and thermal management systems to regulate power conversion and maintain optimal performance without overheating.
With the rise of 800 V EV batteries, faster and more efficient ultra-fast chargers can charge vehicles quicker, taking advantage of the higher voltage to reduce charging times further. To meet the growing demand for such high-performance charging, there is a shift toward modular charging cabins, which can be upgraded easily or scaled as needed. Additionally, the increasing integration of renewable energy sources, such as solar canopies and wind turbines, is becoming common at DC charging stations, helping to power vehicles with cleaner energy.
.svg "Block diagram of a DC EV fast charging station")
DC converter topologies and functionality
In the context of EV charging, both two-level and three-level topologies are used in the PFC stage converting AC power from the grid to DC. The selection is based on the different requirements: total cost, system efficiency, space and control complexity.
The three-phase boost rectifier, also known as an Active Front End (AFE), is a highly suitable two-level topology for the power factor correction (PFC) stage of EV chargers due to its simplified structure, bidirectional operation, simple control scheme and high efficiency. Despite its simplicity, a key limitation is the high conduction losses caused by current passing through the power transistors, as well as recovery losses of body diodes at high switching frequencies. The optimal solution involves using Wide Bandgap (WBG) semiconductors, with each channel requiring either two 1200 V SiC MOSFETs such as Nexperia’s NSF030120L4A0 or a half-bridge SiC power module in an 800 V charging system. While WBG semiconductors significantly improve efficiency and reduce losses, they are more expensive and require careful thermal management. Designers must consider the trade-off between higher initial costs and long-term benefits in terms of performance and design complexity.
-02.svg "Active Front End - 2-level topology")
To address the above mentioned limitations of a two-level topology, design engineers can opt for three-level topologies. They provide similarly excellent performance by reducing harmonics, enhancing efficiency, offering smoother waveforms with reduced voltage stress on the switches; leading to a cost-optimized solution.
The Vienna PFC is an excellent option for three-phase high-power DC EV charging modules with 400 / 800 V output due to its simple circuit design. Each phase uses two rectifier diodes and two back-to-back power transistors, controlled by a single gate driver, eliminating concerns about dead time. This design is cost-effective, as it reduces the number of gate drivers while allowing for 800-1000 V output using 650 V IGBTs such as Nexperia’s NGW75T65H3DFP. As a three-level Neutral Point Clamped (NPC) topology, Vienna PFC offers better power loss, improved EMI performance, and reduced current ripple compared to two-level topologies like conventional boost PFC. However, it requires more components and managing neutral point imbalance can be challenging.
-01.svg "Vienna PFC - 3-level topology")
Future trends and innovations in EV charging
The future of EV charging is filled with exciting innovations. Ultra-fast charging is advancing, increasing the charging power above 350 kW for example to reduce charging times to under 10 minutes. Making EV charging as convenient as traditional refueling. A promising alternative is wireless charging, offering convenience for EV owners by allowing charging without the need for physical connectors. This technology could be particularly beneficial for urban environments and autonomous vehicles, where seamless energy transfer is essential.
Semiconductor advancements will be central to these developments. New materials and technologies are expected to increase charging speeds further, improve system efficiency, and support the integration of renewable energy into charging networks. As the world continues to switch to electric mobility, the evolution of EV charging infrastructure will play a pivotal role in shaping a sustainable and efficient future.
