High Voltage Current Protection in Electric Vehicles

Electric vehicles have become a huge market actively seized by global automobile manufacturers. Efficient and safe driving of electric vehicles requires complete high voltage / current isolation and protection among various subsystems. This text will introduce the system composition of electric vehicles and relevant electric isolation solution for you.

Types of Electric Vehicles: BEV, PHEV, FHEV

Automobile manufacturers all over the world have successively announced the plan of new type vehicles, including battery electric vehicles (BEV), plug-in hybrid electric vehicles (PHEV) and full hybrid electric vehicles (FHEV). Along with the fact that vehicle design is changing into electrification, high-wattage power electronic devices have become the key component of drivetrain and battery system. These high-wattage power electronic devices need to conduct communication and control with low voltage digital controllers, which require electrical isolation between low voltage side and high-power system. Among these applications, galvanic isolation is required to allow the safely interface between digital controllers and high voltage systems of modern electric vehicles.

Battery Management Systems for Electric Vehicles

The electric power part of the electric vehicle system is commonly composed by four major circuit modules including battery management system (BMS) which conducts battery cells monitoring and management in order to ensure efficiency and safety as well as controls charging, state of health, depth of discharge and conditioning of individual battery cells. Second, it includes DC / DC converter used to connect high-voltage batteries to the internal 12V DC network. This network also provides power for the accessories and bias for local switching converters. In addition, it includes on-board charger (OBC) which is composed by AC to DC converters with power factor correction. It can also provide energy storage for lithium ion batteries with battery management system monitoring. The last one is a traction inverter which can drive the electric motors and can be used for regenerative braking or return the unused energy to the battery.

BMS manages the electric power stored in non-board high voltage (HV) batteries and provides power for other parts of the vehicle. The major functions include battery balancing, battery health and wear leveling, charge and discharge monitoring and safety assurance. These functions require galvanic isolation and a division between low and high voltage domain to ensure safe and efficient battery voltage output and isolate voltage sensors for the whole battery pack. In terms of current, it is required to ensure the battery without overloading or higher charging rate and isolate current sensors for monitoring discharging and charging current. In terms of communication, it adopts CAN or serial bus to transmit data by modules and uses digital isolators to make safe and reliable communication possible.

Electric Vehicle & Hybrid Electric DC/DC Converters

DC / DC converters are used to convert direct voltage from one voltage domain to another voltage domain in order to power various auxiliary systems. Isolation products have many uses in DC-DC converters in the electrical domains of electric vehicles or hybrid electric vehicles. These functions require galvanic isolation in order to isolate the control system and avoid high-voltage impact in the following areas like converters achieved by silicon FETs, IGBTs or SiC FETs, converters with input and output from four high / low side switches isolation gate drivers and isolation voltage sensors, data communication and sensing of closed-loop control and isolators used in digital CAN or other bus types.

OBC converts the alternating current power supply of external charging sources into direct voltage, which is used for charging vehicle battery pack. In addition, OBC has the functions like electric charging rate monitoring and protection etc. In the OBC system, isolation gate drivers are used for chop the input signals into switched square wave to provide output direct voltage required by drive transformer generation. This output voltage can be monitored, which uses isolation analogy sensors to provide closed-loop feedback to the system controller. What’s more, the bus with or without digital isolators of integrated DC / DC power converter can conduct monitoring and controlling for the whole system via an isolated CAN bus.

EV Traction Inverters

Traction inverters are used to convert the high voltage of battery or DC bus into the multi-phase alternating current for driving traction motor. Isolation products have numerous uses in the traction inverters of electric vehicle or hybrid electric vehicle driving system, including inverter solutions suitable for silicon FETs, IGBTs or SiC FETs and six high / low side switches isolation gate driver. It can choose DC-DC voltage booster in order to increase the voltage of high-voltage batteries. When used in hybrid power generators, it requires a 2-switch isolation gate driver that conducts battery charge during internal combustion engine (ICE) operation and provides the driver for high / low side switches.

Conclusion: The Best EV Circuit Protection Options

The driving system of electric vehicles is facing the environment with high voltage and electronic noise, which requires stable and high performance current isolation to ensure safe and reliable operation. Compared with traditional optical coupler solutions, the isolation technique based on semiconductors has evident advantages, which makes it the ideal choice for strict electric vehicle applications.

With over ten years of experience in the automobile market, Silicon Labs can satisfy automobile standards and customer requirements, which is the provider of top-level digital isolation solutions facing OEM and tier one electric vehicle suppliers with the shipment of over 30 million. According with AECQ100 automobile grade standard, it has enhanced manufacturing capacity and ultra-low product defect for providing wide isolation product mix, including abundant digital isolators, isolation gate drivers and voltage / current sensors that have passed the market qualification authentication and can provide complete technical support and excellent system performance.

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