Avnet Americas’ director, lighting and transportation, Jason Skoczen, highlights how reference designs are helping engineers meet demand for fast, small and efficient DC fast chargers.
Development of safe and efficient EV charging systems necessitates the integration of advanced technologies across multiple domains. This includes the power stage, which leverages wide-bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN), along with specialized passive components, cabling, cooling and protection for high-power applications.
Wireless connectivity options (cellular, Wi-Fi, Bluetooth) and wired solutions (power line communication, single pair Ethernet) ensure reliable communication. Furthermore, charge controllers integrate diverse microcontroller units (MCUs) and microprocessor units (MPUs), while Internet of Things (IoT) edge computing drives advanced bidirectional charging experiences such as vehicle-to-grid (V2G) functionalities.
EVs can charge at various speeds using specialized electric vehicle supply equipment (EVSE).
EV charging is regulated by a combination of international and regional standards, which cover a wide range of topics, including safety, interoperability, payment methods, physical connectors and communication protocols. The primary categories and critical standards are:
Connectors, inlets, plug types and electrical specifications (hardware): These standards specify the physical plug and socket and the electrical characteristics for power transmission. The international reference standard is IEC 62196, which corresponds to the national standards SAE J1772, GB/T 20234 and CHAdeMO.
Communication protocols (software and interoperability): Standards such as the ISO15118 define the high-level communication protocol that enables EVs and charging stations (EVSEs) to communicate, handling the charging and discharging of the EV’s high-voltage battery. It includes V2G communication, a feature available with bidirectional charging.
Safety and performance standards: IEC 61851 is an international standard that specifies the basic requirements for conductive charging systems, including safety features and charging modes (Modes 1, 2, 3 and 4). It addresses the characteristics and operating conditions of the EV supply equipment, the specification of the connection between the EV supply equipment and the EV supply equipment’s electrical safety standards.
DC fast charging (DCFC) represents the most advanced system of EV infrastructure. It enables rapid and high-power energy transfer and is ideal for public charging stations and long-distance travel.
As EV batteries evolve toward higher voltages, WBG solutions, such as SiC and GaN, play a pivotal role. Due to their faster switching speeds and higher efficiency, high-temperature operation and higher voltage/power handling capabilities, EV charging stations will become more efficient and compact.
The key components of DCFC are:
A three-phase AC input and power conditioning: Before conversion, the power passes through EMI/RFI filters, which suppress high-frequency noise to ensure clean power delivery, and surge protection devices, which guard against voltage spikes from grid fluctuations.
Active rectifier with power factor correction (PFC): Three-level, three-phase Vienna rectifier reference designs with digital control for power factor correction and based on SiC MOSFETs can achieve nearly 99 per cent efficiency.
A high-voltage DC link where DC power is stored in a capacitor bank (800 to 1000 V).
An isolated bidirectional DC/DC converter to adjust the voltage to match the EV battery’s requirements (typically 400, 800 or even 1,000 V). Topologies like LLC resonant converters or dual active bridge (DAB) are used for high efficiency. Some systems also support bidirectional power flow, enabling V2G applications.
Output contactors and sensors: High-current contactors safely connect and disconnect the charging circuit, while sensors monitor voltage, current and temperature in real time.
Liquid-cooled charging cables reduce heat buildup and allow for thinner, more flexible designs.
Control and auxiliary systems: A centralized MCU/MPU manages the entire charging process, including communication protocols, protection mechanisms, HMI and liquid cooling systems for power modules and cables.
Avnet also offers a 25 kW SiC-based DC charger reference design intended as a modular foundation for accelerating the development of Level 3 fast EV chargers. The architecture features two fully independent boards: a six-pack three-phase AC-DC converter with power factor correction (PFC), and a dual-active bridge isolated DC-DC stage. These are linked via an intermediate 800 V DC bus.
Designed for compatibility with global grid voltages, the system can deliver up to 50 A of output charging current. When up to 12 of these modules are connected in parallel, the system can supply 300 kW of power from a single charger cabinet. This cabinet can communicate directly with the EV battery and is programmable through a user interface. By leveraging this design as a baseline, manufacturers can develop the user interface in parallel with hardware, streamlining the overall development process.
To streamline the design of an EVSE, development platforms featuring Linux OS and Wi-Fi 6 offer a complete toolkit, including software, hardware boards, cables, design files and step-by-step instructions to rapidly simulate a charging control session between an EV and a charging station. They are ideal for developing key features such as secure wireless cloud connectivity, precise energy metering, reliable safety control, one-tap NFC authentication and ISO 15118 power line communication over HomePlug Green PHY.
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