EliteSiC Solutions for EV Charging
Overview
The boom in the EV market has spurred the development of various industries, with EV charger undoubtedly being one of the most incentivized applications. To meet the growing needs of EV, more and faster charging infrastructures need to be established. Simultaneously, as a crucial means to achieve low-carbon goals, EV charging devices need to be designed efficiently.
The trend towards higher power and greater efficiency in charging modules is expected. By adopting suitable power components and topologies, along with robust controllers, we will have more high-power charging stations, addressing range anxiety and reducing carbon emissions.
Power conversion stages
The DC EV charger consists of a classic power conversion stage of AC-DC and DC-DC. The front end of the DC charger consists of a three-phase Power Factor Correction (PFC) boost stage, it could be implemented in a variety of topologies (two or three level) and uni- or bi-directional. See AND90142 - Demystifying Three Phase Power Factor Correction Topologies to understand three level and example three level PFC circuit. The voltage level from the grid 400 V - 480 V (Three-phase) / 110 V – 240 V (Single-phase) is boosted up to 500 – 1000 V (and targeting higher). A subsequent DC-DC isolated stage converts the bus voltage into the required output voltage. The output voltage aligns with EV battery voltages (typically 400V or 800V) and need to cover the voltage charging profiles. Therefore, the DC-DC output range might swing from 150V up to 1000V. Specific implementations might be optimized for the 400 V or 800 V level.
The overall system efficiency of a DC EV charger is nowadays around 95%, main losses come from power conversion, cable, transformer. In a high-power system, even 1% losses generate massive heat, so improving efficiency is always a target for charger designers.
DC wallbox (charger)
DC wallbox (charger) is considered a replacement for traditional low-power AC chargers installed in places like parking lots, houses, offices, etc. It must be compact, lightweight and cost-effective. The key value of DC wallbox is that it defines the charging power rather than relying on an OBC. (AC charger is a simple system containing electricity meter and communication interfaces, without a high-power conversion stage.) With adoption of DC wallboxes, some manufacturers consider removing the OBC from their future EVs to decrease vehicle cost. However, this would also bring inconveniences as AC chargers can not be used.
Communication
Communication and connectivity are cornerstones of EV Chargers, fulfilling different functions: between stacked modules on the power stage, CAN, PLC, RS485, which depends on charger OEMs. Between vehicle and charger for the charging sequence. CAN or PLC are usually used. External connectivity for payment, service management, maintenance, software upgrades, preferred communication methods are BLE, Wi-Fi, 4G/5G.
Compliance and standard
There are several standards and protocols worldwide that define the requirements for DC charging, such as the IEC-61851 / SAE1772, GB/T, standards and the CHAdeMO, Combined Charging System (CCS) or Tesla Supercharger protocols. IEC 61000-3-2/4 defines the limitations of harmonics in power.
Discrete vs Power module
There are lots of aspects which influence customer‘s decision, but for high-power products, module solution is highly recommended especially when dealing with multiple discrete MOSFET/IGBT in parallel. Module approach will improve aspects such as the long-term performance caused by imbalanced current and heat, switching timing, wiring connections, etc. Read AND9100 – Paralleling of IGBTs to learn more.