Onsemi to Supply High-Voltage Components for Kempower EV Fast Charging Solutions

May 27, 2023 by Mike Falter

Onsemi has announced a strategic agreement with Kempower to provide high-voltage EliteSiC MOSFETs and diodes for Kempower’s EV fast-charging solutions.

Onsemi has announced a new strategic agreement with Kempower to supply EliteSiC MOSFET and diode technology for use in Kempower’s Satellite DC fast chargers.   

Kempower Satellite DC fast chargers

Kempower Satellite DC fast chargers. Image used courtesy of Kempower

As the transition to electric vehicles continues, a reliable charging infrastructure to support their use remains a challenge. For broad adoption of EVs, drivers need easy access to chargers capable of quickly charging their vehicle batteries.

Government policies like the Bipartisan Infrastructure Law are incentivizing commercial rollout of EV charging stations, and emerging technologies like DC fast charging are providing the capabilities needed for EV drivers to rapidly replenish their batteries while on the road.

According to Kempower, the company is choosing onsemi’s EliteSiC technology to improve the size, weight, and efficiency of their Satellite DC fast chargers. Under the agreement, Kempower will be using onsemi’s EliteSiC D3 diodes and M3S MOSFETs in the high voltage AC-DC rectification and DC-DC conversion circuits that form the core of their Satellite EV charging platform.


DC Fast Charging

This latest announcement from onsemi follows similar announcements in the past few months with leading e-OEMs Volkswagen (VW) and BMW. In those supply agreements, onsemi’s EliteSiC technology will be used for similar power conversion circuits in the EV’s onboard traction inverter. This circuit converts the DC battery voltage to three-phase AC for powering the EV motor.

Similar but opposite to the function of a traction inverter, a DC fast charger is a rectification circuit that converts utility grade, three-phase AC to high voltage DC for direct charging of an EV’s battery pack. A typical DC fast charger comprises two stages, the AC-DC rectification and power factor correction stage and a transformer-isolated DC-DC conversion stage that generates the regulated DC voltage needed to charge the vehicle batteries.   

The high voltage of a DC fast charger is the “secret sauce” that makes them “fast,” allowing them to deliver more power (several hundred kW) with fewer I2R losses. Because of the high voltages, and direct DC output, Level 3 fast chargers typically bypass an EV’s onboard charging (OBC) circuit, designed to rectify the lower AC voltages of single and three-phase Level 1 and 2 chargers.

A single-phase, 120 VAC, Level 1 charger is typically found in a residential home for overnight EV charging, while public-use DC fast chargers can charge EV batteries in tens of minutes instead of hours.  


DC fast-charger functional blocks

DC fast-charger functional blocks. Image used courtesy of onsemi

Satellite DC Fast-Charging Platform

According to published specifications, each Satellite DC fast charger can deliver up to 240 kW (300 A at 800 VDC) through a single CSS connector.   

While not a mobile platform, size, and weight are critical features for Kempower’s Satellite chargers as they are designed for easy installation by charge point operators, even in tight spaces.  

The Satellite charger is designed to be a flexible platform, accommodating both 400 VDC and 800 VDC charge voltages and compatible with CCS2 and CHAdeMO charging cable connector types. 

Each charging station supports Wi-Fi, cellular, and Ethernet connectivity for cloud communications, and stations are scalable to the needs of charging system operators – existing gas stations and convenience stores, new station build-outs, commercial facilities, charging network providers, or any location looking to add DC fast-charging capabilities.  


Dual-output Satellite DC fast charger

Dual-output Satellite DC fast charger. Image used courtesy of Kempower

Power is provided to the Satellite chargers with one or more Kempower Power Units (CPU), each individually capable of delivering up to 200 kW of DC power, or 600 kW when three cabinets are operated together.

The CPUs receive 380 to 480 VAC, 50/60 Hz line power at the input, and deliver up to 920 VDC at the output, with 94% conversion efficiency at full load. The output voltage specification is particularly important since it allows the units to accommodate the 800 V battery buses that are increasingly common in EVs.   

A triple cabinet CPU can supply eight charging outputs across eight single or four double-port Satellite chargers.  

Triple-cabinet CPU

A triple-cabinet CPU can power eight fast charge outputs. Image used courtesy of Kempower


Low Capacitance Contributes to EliteSiC Performance

According to onsemi, their EliteSiC components reduce system size and weight due to their high efficiency and lower power losses, even at high frequencies. The low on resistances and minimal gate and output capacitances of the EliteSiC power devices contribute to this performance. Lower capacitances improve efficiency and switching performance at higher frequencies, translating to smaller components and solution sizes.


M3S MOSFET capacitance vs. drain-to-source voltage

M3S MOSFET capacitance vs. drain-to-source voltage (VDS). Image used courtesy of onsemi

Onsemi’s M3S series of power MOSFETs and D3 diodes are rated to 1200 V, suitable for 800 V DC fast-charging applications.