Electric vehicles (EVs) are a rapidly growing segment of the automotive industry owing to the improved technology, low carbon footprints, and government policy incentives. Currently, the electric vehicle industry is undergoing a technological transformation to improve vehicle range with charging infrastructure. Electric vehicle automakers and charge service enterprise are investing heavily in charging station infrastructure in order to support long-range battery electric vehicles and improve EV drivers’ experience.  Government incentives and automakers’ initiatives for charging infrastructure development are the key factors driving the growth of the global electric vehicle charging stations market. The market is projected to reach around UDS 30 billion by 2027 at a CAGR of 36% from 2019 , based on Meticulous Market Research report. The level 3 DC charging station sub-segment is accounted for the largest share of the overall electric vehicle charging stations market and Asia pacific will command near 50% of the market during the forecast period.  The large share of this segment is mainly attributed to rising demand for setting up of charging infrastructure at convenient urban commercial sites. Expensive commercial real estate drives investors and developers to squeeze charger pile sizes and increase charging power.  That leads to the increasing demand of high density charger pile modules.  To achieve high density design, the power converters need to operate at higher switching frequency with an equal or better efficiency.

Currently, charger pile modules of the state of art design and in volume production almost all use 650V Si MOSFETs in order to get a decent power density and efficiency out. For a design with power over 6 kW, 3-phase input becomes necessary. Since the intermediate bus voltage exceeds 650V device rating requirement, three-level topologies or series-connected converters are the only choice for the design.  Fig.1 and Fig.2 are two commonly-used isolated charger pile topology structures.  If a charger station has a local isolated power transformer, non-isolated converter topologies can be used. Fig. 3 is a non-isolated topology, which has been by EU 350kW ultra-fast charging station design. Each charger pile (point) consists of 6 60kW fully SiC-based power converter modules. 

 Fig. 1.  A charger pile using a Vienna PFC and a three-level phase-shifted full bridge DC/DC converter

 Fig. 2.  A charger pile using a Vienna PFC and a series-connected three-phase LLC DC/DC converter

        If a charger station has a local isolated power transformer, non-isolated converter topologies can be used. Fig. 3 is a non-isolated topology, which has been by EU 350kW ultra-fast charging station design. Each charger pile (point) consists of 6 60kW fully SiC-based power converter modules.  

图3 非隔离充电器使用维也纳PFC和串连的Buck DC/DC变换器

For isolated charger pile design, high-voltage and high-frequency capabilities of SiC MOSFETs can simplify topologies and controls significantly. The direct benefit is power density improvement and system cost reduction.  By using 1200V SiC MOSFETs, PFC’s output voltage can have a range from 600V to 900V. With a controllable voltage-doubler output and switched-transformer windings, the downstream isolated DC/DC converter can operate at ideal DC transformer (DCX )mode to optimize system efficiency. As the DCX output is connected to a battery pack directly, its input appears to be a voltage source, which makes it possible to reduce or even eliminate PFC output bulk capacitors. The function block of this new power architecture is shown in Fig. 4.

Fig.4. New AC/DC power architecture for battery charging

Based on this power architecture, the following topology structure of Fig.5 can be used to serve wide output voltage and constant power battery charging purposes.  Switch K is used to select transformer turn ratio and enable voltage doubler to extend the output voltage range. Fig. 6 shows the relationship between the PFC output voltage and the battery voltage.

Fig.5. High density power architecture for battery charging

Fig.6. DC Transformer gain switching

The following are the 3-phase PFC and DCX prototype photos.  The circuit is still under optimization.  We welcome any interested parties to join this development and turn it into a real product.

 Fig.7. (a) 20kW three-phase PFC prototype

Fig.7.   (b) 20kW LLC converter prototype