High-power dc fast charging is transforming how electric vehicles (EVs) interact with the grid. As site power levels climb from 150 to 350 kW and beyond, engineers are faced with new challenges. These include maintaining grid stability, managing thermal loads, and ensuring safety and reliability across increasingly complex charging networks.
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Mike Calise, CEO of Tellus Power.
To explore the engineering decisions behind today’s fast-charging infrastructure, we spoke with Mike Calise, CEO of Tellus Power, a company focused on advancing scalable, efficient, and grid-resilient EV charging solutions.
Calise discusses how engineers are addressing key design priorities such as grid integration, modularity, high-voltage isolation, and system reliability as charging networks continue to expand worldwide.
Part I covers strategies for grid stability, modular design, and electrical safety in high-power dc charging. Part II examines advances in thermal management, interoperability, and the evolving role of vehicle-to-grid (V2G) integration.
Here’s what he had to say…
How do engineers ensure grid stability when deploying high-power dc fast chargers?
Engineers can ensure grid stability when deploying high-power direct current fast chargers (DCFCs) by implementing load management and integrating on-site energy solutions. Smart charging and advanced load management software are the primary tools, actively adjusting power delivery to vehicles based on current grid conditions and local demand. This prevents overloading distribution transformers and feeders, which is crucial since the unpredictable nature of EV charging can cause voltage fluctuations, leading to brownouts or blackouts.
By analyzing complex load profiles, engineers can shift charging to off-peak hours, a strategy that mitigates the need for expensive grid upgrades and maintains a reliable power supply.
Large-scale EV charging sites can significantly increase electricity demand, straining local distribution networks and creating power quality (PQ) issues such as power factor and harmonic disturbances. Large charging sites also require specific design infrastructure to minimize those PQ issues. One specific design element is that sites should avoid single, large kVA site transformers and instead use multiple transformers (phase shifting pairs or multiple secondary winding transformers) to offset harmonic content.
For enhanced resilience and power quality, engineers can also deploy Battery Energy Storage Systems (BESS). These systems act as a buffer, storing energy during low-demand periods or from renewable sources and discharging it to meet peak charging loads. This reduces the instantaneous power draw from the grid and helps with ancillary services like frequency regulation and voltage support. It also helps to combat the harmonic distortion and poor power factor introduced by the high-power dc conversion, specific infrastructure designs are used. Instead of single, large transformers, engineers often use phase-shifting transformers or multiple secondary winding transformers to cancel out harmonic currents.
This multi-pronged approach ensures that large-scale EV charging can be integrated into the grid without compromising its stability or efficiency.
What role does modular design play in scaling charger power levels from 150 to 350 kW and beyond?
Modular design plays a crucial role in scaling charging power levels. They help ensure high reliability and uptime of the system as one single power module failure should not affect the other modules, so the whole charger system can still perform and just derate the total system power depending on the module size.
In the meantime, the service technician can plan service dispatch and fix/replace the module. In most cases drivers may not notice the failure because not many cars can take that much power.
Modular designs are also a future-proof CPO investment: they can start with a lower power level according to the current planning, budget or infrastructure, with conduit and infrastructure planned in advance for future upgrade during the initial install. Later, as demand for power increases, the CPO does not need to replace the charger; they only need to add more power modules to upgrade.
What are the key safety considerations for high-voltage isolation, grounding, and fault detection in dc fast-charging systems?
A technician assembles the internal power and control components of a dc fast charger during system integration.
Site design and construction for DCFC systems must start with stringent grounding grid design, as well as installation and assurance testing. High-voltage isolation is achieved through insulation and specialized devices, such as Insulation Monitoring Devices (IMDs), which continuously check for dangerous drops in resistance between the high-voltage lines and the system’s chassis.
If a fault is detected, the IMD triggers an immediate shutdown, preventing an electrical short and protecting anyone who might encounter the equipment. This is paired with a rigorously designed grounding grid that provides a safe, low-impedance path for any fault currents, ensuring that safety sensors and circuit protection devices function correctly.
To further enhance safety, DCFC systems use multiple layers of fault detection and protection. This includes coordinated short-circuit protection, a series of circuit breakers and fuses strategically sized to trip in a specific order, limiting the duration and destructive energy of a fault.
Additionally, systems are equipped with surge protection devices (SPDs) to shield sensitive electronic controls from power spikes, which could otherwise lead to system malfunctions and safety hazards. During the final commissioning process, engineers perform a comprehensive check of all safety features.
The review process includes testing emergency stop switches and verifying that all safety labels and drawings are in compliance with regulations like the National Electrical Code (NEC), ensuring the system is safe and reliable before it becomes operational.
How do engineers balance uptime, reliability, and serviceability in fast chargers that see heavy daily use?
Engineers can balance uptime, reliability, and serviceability in heavily used fast chargers by implementing a strategy focused on proactive management and efficient maintenance. They use remote monitoring systems with proactive alerts to detect potential component degradation or failures before they impact service, allowing for preventative actions.
When an issue arises, remote diagnostics and troubleshooting tools can be employed to resolve problems without a technician visit, significantly reducing downtime and operational costs.
For onsite repairs, a single truck roll is the goal; this is achieved by providing technicians with comprehensive data on the failure, including its root cause, a detailed remedy plan, and the necessary replacement parts and standard operating procedures (SOPs). Additionally, system modularity and an optimized power module design are crucial.
A modular design ensures that components can be quickly and easily swapped out in the field, minimizing the time a charger is out of service. An optimized power module design, often with redundant modules, ensures that the failure of one module does not disrupt the entire charging operation, maintaining a high level of availability and reliability.
Established petroleum service companies with mature logistics continue to play a crucial role in balancing reliability and serviceability in fast chargers these days. Local maintenance depots, spare parts inventory, and qualified certified technicians keep gas pumps, POS terminals, and now DCFC uptimes high for this industry. These companies, plus established electrical operations and maintenance companies have expertise in DCFC uptime ensuring customer satisfaction with guaranteed response times through service level agreements.
As the deployment of high-power dc charging accelerates, engineers are strengthening the underlying systems that keep these networks safe, efficient, and reliable. Part II of this interview focuses on the next frontier of fast-charging technology, including thermal management, cable and connector innovations, interoperability, and the growing role of vehicle-to-grid (V2G) integration.
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