The growth in the electric vehicle (EV) market is being matched by the in-kind growth of the EV charging market. In order for EVs to be more fully accepted, though, charging must be made faster, and this usually happens through the use of higher levels of power. In this article, learn how galvanic isolation, specifically isolation technology from Skyworks, is enabling the next generation of high-power EV charging systems.
Introduction
As automotive designs move to electrification, high-wattage power electronics become critical components in the new electronic drive train and battery systems. These high-wattage electronics need to be communicated with and controlled by low-voltage digital controllers requiring electrical isolation of the low-voltage side from the high-power system. In these applications, galvanic isolation, usually semiconductor-based isolation, is required to allow the digital controllers to safely interface with the high voltage systems of a modern EV.
EV System Overview
EV/HEV battery management systems typically include four major circuit assemblies, each with specific isolation needs.
Battery management system (BMS): Battery cells are monitored and managed by the BMS to ensure high efficiency and safety. The BMS controls the charge, state of health, depth of discharge, and conditioning of individual battery cells.
Where Isolation is Needed in a BMS
- Voltage: Assure safe and useful battery voltage output
- Isolated voltage sensor for the full battery stack
- Current: Protect batteries from overload or high charging rates
- Isolated current sensor monitors discharge and charge current
- Communications: CAN or serial bus for module data
- Digital isolators enable safe and robust communication
DC/DC converter: The dc/dc converter connects the high-voltage battery to the internal 12 V DC network, which also provides power to the accessories and bias to the local switching converters.
Where Isolation is Needed in a DC/DC Converter
- Converters: Implemented with silicon FETs, IGBTs, or SiC FETs
- Isolated gate drivers for the four high/low-side switches
- Isolated voltage sensor for input and output of the converter
- Communications and Sensing: Data for closed-loop control
- Isolators for digital CAN or other bus types
On-board charger (OBC): Energy storage is provided by Lithium-Ion batteries charged by an onboard charger consisting of an ac-to-dc converter with power factor correction and supervised by a battery management system.
Where Isolation is Needed in an On-Board Charger
- Communication buses: CAN and SPI
- Transformer synchronization
- Monitoring charging current or battery voltage
Traction Inverter: The main inverter drives the electric motor and is also used for regenerative braking and returning unused energy to the battery.
Where Isolation is Needed in a Traction Inverter
- Inverter: Solutions available for silicon FETs, IGBTs, or SiC FETs
- Isolated gate drivers for the six high/low-side switches
- Booster: Optional dc-dc booster to increase HV battery voltage
- Isolated gate drivers needed for 2 switches
- Generator (Hybrid): Recharges battery when ICE is running
- Isolated gate drivers for high/low-side switches
Conclusion
The race to electrify automotive fleets is accelerating with more vehicles arriving from more manufacturers every year. This increase in the number and type of EVs creates opportunities for electronic suppliers to grow their device footprint in the vehicle’s power electronics systems. The high voltages and noisy environments in these drive systems require robust, high-performance galvanic isolation to ensure safe and reliable operation.