Three design considerations for EV charging

Typical electric vehicle (EV) charging station designs for commercial and residential use include energy metering, residual current detection (AC and DC), isolation safety compliance, relays and contactors , as well as drive functions, two-way communication, and service and User Interface. While the goal of a charging station is to efficiently transfer power to a vehicle, enabling power transfer is only its original function.

 

According to a new report from IHS Markit, an estimated 20 million public electric vehicle charging stations will be connected to the grid by 2030, and the size of community charging stations is expected to expand significantly to meet demand. Electric vehicle charging station design contains unique challenges. Electric Vehicle Supply Equipment (EVSE) must combine communication, functional safety and information security capabilities while providing an easy upgrade path to accommodate future grid integration. In this article, I will briefly describe three design considerations for using TI's SitaraTM AM625 for a Level 2 AC electric vehicle charging station in a scalable hardware and software case. 

 

Design Consideration 1: Understanding Future Communication Standards and Grid Integration

Electric vehicles of the future are expected to be a source of energy, returning stored energy to the grid during periods of peak demand or power outages. Managing this potential energy exchange is an aspect of grid integration that makes communication a key design consideration for EV charging stations. Whether it is from the vehicle charging point to the power grid or the charging station to the cloud, the front-end and back-end communication design must meet the data, functional safety and information security standards during the charging process, as shown in Figure 1.


V2G technology

The International Organization for Standardization (ISO) 15118 standard outlines a two-way communication protocol between an electric vehicle and a charging station that can exchange information such as vehicle identification, charging control, and charging status, enabling features such as plug-and-charge. Covering front-end and back-end communication requirements to meet ISO 15118 standards not only meets compliance today, but also enables long-term suitability of designs for future grid integration.

 

Selecting the right processor integration and software functions today enables simple optimization for future grid integration. The SitaraTM AM625 used in the EV charging design shown in Figure 2 includes a mainline Linux® kernel with a standard software development kit to ensure efficient maintenance and simplified updates. The AM625 processor also supports secure boot for IP protection, has a built-in Hardware Security Module (HSM), and employs advanced power management support to optimize system power consumption at idle.

AC Charger Block Diagram; DC Charger Block Diagram

AC Charger Block Diagram; DC Charger Block Diagram

Design Consideration 2: Utilize a Module-Based Design for Flexible AC or DC Charging Options

Determining the right connectivity solution for an EV charger includes considering its use case, installation environment, and extensions for grid integration. Commercial EV chargers often require cloud connectivity to manage billing, power distribution, and vehicle data insights, and you may want to consider the ability to centralize data management across multiple charging points. Residential chargers will eventually become an extension of the smart home, requiring integration with existing wired and wireless networks.

The Open Charging Protocol (OCPP) is a standard that defines communication between charging stations and a network of charging stations that manages the exchange of data. Designing for this protocol requires multiple connectivity options, either via Ethernet , cellular, Wi-Fi® or Sub-1GHz signals.

To meet the challenge of flexibly meeting the OCPP, EV chargers need to have multiple connectivity options. For example, WiFi is everywhere. As such, it can be used to connect EV chargers to existing infrastructure, or to provide local connectivity to networks of charging stations where wired connections are not feasible. Low-frequency communications such as Sub-1GHz outperform LTE in connection reliability when EV chargers are deployed in challenging RF environments such as underground parking lots . Whether the design is for commercial or residential use, or where the charger is located, the design requires a flexible and reliable connectivity solution.

Choosing the right connection solution means supporting a higher operating temperature range, ensuring stable connections even in harsh environments with large temperature changes. Also, ensure interoperability with business or home networks. TI's WL1837MOD WiLinkTM 8 module provides excellent RF performance and robust interoperability with other WiFi devices. It also integrates Bluetooth for easy configuration and deployment. Combined with Phytec's high-volume Phycor-am62x multi-core Arm® processor system-on-modules, the WL1837MOD provides ecosystem software compatibility, ease of third-party software integration, and migration and optimization for future OCPP 2.0.1 and later versions Provide an upgrade path.

Design Consideration 3: Manage longevity through information security and functional safety options.

As the future of ISO 15118 and OCPP 2.0.1 moves towards improved data insights (on both vehicle and user data), secure software is critical for both connectivity and communication. The processor will play a key role in enabling future EV charging scalability, both as a system monitor for monitoring data quality and charging levels, and as a secure gateway for insight into payment and vehicle data.

ISO 15118 supports data security at both the application and transport layers. Transport Layer Security (TLS) 1.2 or later encrypts transport layer communications. While ISO 15118-2's TLS is only mandatory when plug-and-charge identification mechanisms are used, TLS is mandatory for all use cases and all identification mechanisms in the future ISO 15118-20 standard. AM625 has on-board HSM information security features such as:

Safe Boot:

Self-programming hardware (eFuse) keys.

Encrypted and authenticated boot is supported.

Debug (Joint Action Group) port.

Off by default on high security devices.

The eFuse setting allows permanent shutdown.

Every EV charging design includes multiple safety aspects, including safe cabling, ground fault monitoring, relay actuation, and high voltage isolation. TI's DRV8220 motor driver IC features an integrated H-bridge, logic control and protection for easy plug locking, ground fault monitoring and relay drivers.

Epilogue

The electric vehicle charging industry continues to evolve, becoming more standardized, smart and efficient. Designers must consider flexible connectivity and security for long-term integration with the grid. Choosing the right processor design requires consideration of growing data processing demands and the need for a reliable software stack. 

 

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