Developing DC Fast Chargers for Smart Grids:Deep Technical Insights from PHYTEC

As part of the Five-Day Online Faculty Development Programme on “Advanced Power and Energy Networks: AI, Cybersecurity, and Quantum Communication for EV-Integrated Smart Grids”, organized from 23–27 February 2026 by the Department of Electrical and Electronics Engineering, Annamacharya University , an insightful technical session was conducted by Mr. B. Vallab Rao, Managing Director, PHYTEC Embedded Pvt. Ltd., Bangalore.

The session moved beyond conceptual overviews and provided a system-level engineering breakdown of DC Fast Charger architecture, covering:

• High-power conversion topology

• Embedded real-time control segregation

• PLC-based EV communication

• ISO 15118 protocol stack

• SLAC pairing

• OCPP cloud connectivity

• PKI-based cybersecurity

• Supporting demand response and load balancing

Unlike AC chargers, DC fast chargers bypass the onboard charger inside the EV and directly supply regulated DC to the battery pack — enabling rapid energy transfer under tightly controlled safety mechanisms.

Layered Architecture of a DC Fast Charger

DC Fast Charging: More Than Just High Power

At its core, a DC Fast Charger converts three-phase AC from the grid into regulated high-voltage DC and delivers it directly to the EV battery. But technically, it is far more than a power converter. It behaves as a smart grid node — capable of digital negotiation, authentication, energy optimization, and backend orchestration.

Unlike AC chargers where conversion happens inside the vehicle, DC fast chargers handle the entire conversion externally. This allows higher power levels (30 kW to 350 kW and beyond), reduced charging time, and tighter control over charging profiles.

From an infrastructure perspective, these systems must ensure:

• High efficiency and harmonic compliance

• Deterministic safety handling

• Secure communication

• Grid-aware energy management

System Architecture: Layered and Deterministic by Design

The charger architecture is divided into clearly isolated domains.

The power stage includes an active front-end rectifier, DC link stage, isolated DC-DC modules, protection circuits, and cooling systems. The design objective is high efficiency and compliance with IEC grid standards.

Above the power layer sits a dual-processor embedded architecture.

The high-level processing is handled by a Linux-based SoM (such as phyCORE-AM62x), which runs:

• ISO 15118 stack

• OCPP client

• TLS security layer

• UI and application services

Meanwhile, a dedicated real-time microcontroller (like MSPM0G3507) handles:

• Control Pilot signal generation

• Proximity detection

• Contactor control

• ADC-based monitoring

• Emergency and fault logic

This separation ensures that safety-critical operations remain deterministic, even if the application processor is busy or rebooting. From a production standpoint, this is essential for compliance and reliability.

SLAC: The First Digital Handshake

Before any high-level communication begins, the EV and charger must establish a reliable Power Line Communication (PLC) link. This is where SLAC (Signal Level Attenuation Characterization) comes into play.

SLAC is part of the HomePlug Green PHY standard. It ensures that the EV pairs with the correct charger and not with another nearby unit. The process involves signal attenuation measurements over the control pilot line. Only after successful attenuation matching does the EV lock onto the charger for communication.

In simplified terms, SLAC answers one critical question:

“Am I talking to the correct charger?”

Without SLAC pairing, ISO 15118 communication cannot proceed.

ISO 15118: The Intelligence Layer

Once PLC pairing is established, communication shifts to TCP/IP over PLC, secured by TLS. At this stage, ISO 15118 governs the interaction between the EV and the charger.

There are different variants of ISO 15118:

ISO 15118-2

Currently the most deployed standard. It supports:

• Plug and Charge (PnC)

• Encrypted TLS communication

• Smart charging negotiation

• Contract-based authentication

ISO 15118-20

The next-generation evolution, enabling:

• Bidirectional charging (V2G)

• Unified AC/DC communication

• Wireless charging support

• Enhanced certificate management

DIN SPEC 70121

An earlier DC charging communication protocol used before ISO 15118 matured. It supports basic DC charging but does not include Plug and Charge functionality.

The communication sequence typically includes:

1. TCP connection setup

2. TLS mutual authentication

3. Certificate validation

4. Service discovery

5. Authorization

6. Charge parameter negotiation

7. Power delivery control

All of this happens automatically within seconds after plug-in.

Plug and Charge: Authentication Without Human Intervention

Plug and Charge eliminates RFID cards and mobile apps. The EV carries a digital contract certificate. When connected, the charger verifies this certificate through a PKI chain and backend validation.

If validated, charging begins automatically.

This model improves user experience while maintaining high cybersecurity standards.

Cybersecurity: A Non-Negotiable Requirement

Because chargers are exposed grid-connected endpoints, security is foundational. The session highlighted:

• X.509 certificate chains

• TLS 1.2/1.3 encryption

• Public Key Infrastructure (PKI)

• Secure boot mechanisms

• Signed firmware updates

Without strong cybersecurity, chargers become potential attack surfaces within smart grids.

OCPP: The Cloud Coordination Layer

While ISO 15118 governs EV-to-charger communication, OCPP manages charger-to-cloud interaction.

Two primary versions were discussed:

• OCPP 1.6 – widely deployed, JSON over WebSockets

• OCPP 2.0.1 – enhanced security, device models, smart charging support

Through OCPP, the backend can:

• Monitor sessions

• Push firmware updates

• Control charging remotely

• Collect diagnostics

• Apply smart charging policies

This enables centralized fleet management and scalable deployment.

Software Intelligence: EVerest Framework

The charger software stack was implemented using the EVerest framework, a modular open-source EVSE platform.

EVerest abstracts hardware layers, integrates protocol stacks, and uses message-driven internal communication. This makes the system scalable, vendor-independent, and future-ready.

Its modularity allows seamless updates when transitioning from ISO 15118-2 to ISO 15118-20 or from OCPP 1.6 to 2.0.1.

From Plug-In to Power Delivery: Real-Time Flow

During the live demonstration, the audience observed the complete state transition sequence:

Idle → EV Detected → SLAC Pairing → TLS Handshake → Authorization → Charging → Termination

Logs clearly showed how firmware, Linux services, protocol stacks, and power modules coordinated in real time.

This practical demonstration bridged theory and deployment.

Final Perspective

DC Fast Chargers represent a convergence of:

• Power electronics engineering

• Real-time embedded systems

• Secure communication stacks

• Cloud-native backend integration

• Smart grid intelligence

They are no longer “chargers.” They are intelligent, software-defined energy assets embedded within modern power networks.

The session successfully aligned academic knowledge with industrial implementation, offering a realistic understanding of how next-generation EV infrastructure is architected and deployed.