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Megawatt charging refers to the delivery of high-power DC charging directly to the EV battery, bypassing the onboard charger. This method significantly reduces charging time compared to standard Level 1 and Level 2 chargers. MW charging is essential for commercial EVs to ensure quick recharges during busy schedules and long trips, supporting fleet efficiency by enabling faster turnaround times and reducing vehicle downtime.
Overview of CCS and MCS:
Combined Charging System (CCS) is a widely used standard for EV charging, supporting both AC and DC charging. Megawatt Charging System (MCS) is designed specifically for high-power DC charging, catering to the needs of commercial EVs.
Key Differences:
Battery Cells:
The speed at which battery cells can be charged is impacted by both temperature and State of Charge (SoC). Sophisticated thermal management and route planning tools can help maximize efficiency.
Battery Size and C-rate:
Higher C-rates enable faster charging but must be balanced by larger battery sizes; balancing costs here is crucial.
Potential Thermal Bottlenecks:
Each element within the battery and charging infrastructure is susceptible to becoming a charge speed constriction point. Effective thermal management systems are required throughout the entire charging system to prevent overheating during high-power charging sessions.
Power Distribution:
Robust power distribution systems are required to ensure stable and safe delivery of high-power DC charging. Eaton's Breaktor and truck series EV fuses can safeguard high-speed charging.
Charging Session:
Enhancing the current limit on either the charger or the vehicle —through thermal mitigation strategies or the augmentation of contactors for example—can elevate the peak charging speed, diminishing the time required for a full charge.
Implementing MW charging for commercial vehicles requires investment in advanced battery systems, robust power electronics and efficient thermal management. Here are four key areas that can impact whether megawatt charging works for an application.
Battery cells are kind of like people: they like similar temperature ranges and must be kept climate controlled. They will work in a wide variety of temperature, but prefer to stay between 15 and 35 deg C. Additionally, the state of charge can impact how quickly the battery can accept a charge.
To enable fast charging, the vehicle must have an advanced thermal management system to keep the battery at a happy temperature AND intelligence like route planning, to know when a charging event may be coming, so it can pre-condition the battery (heating, cooling and regulating the state of charge) for maximum charging performance.
To achieve fast charging, you can either have a really big battery pack or use battery chemistry designed to be fast. There is a cost and durability tradeoff for each scenario which must be considered based on the application. Faster cell chemistry usually comes with additional cost and lower longevity.
The commercial EV market is revealing a preference for Lithium Iron Phosphate (LFP) chemistry for cost and durability. Recent advancements in this chemistry is increasing C rate, but even with a battery rated at 4C, to charge at 3.75MW (the maximum capacity of the MCS standard), you would need nearly 1000kWh of battery in the vehicle. Conversely, charging at 1MW can be accomplished with a 400kWh battery which, while significantly larger than a light vehicle battery, is much more manageable for commercial vehicles.
Another consideration when it comes to charging is thermal limitations. Each component in the battery and charging system has the potential for forming a bottleneck. Losses in the electrical system follow the I2R (copper loss) rule and when dealing with current between 800 and 3000 Amps, small increases in resistance like those around contactors can create massive amounts of heat which must be managed. Eaton has the electrical expertise to help with system analysis to assure correct sizing of all components for commercial vehicles.
Megawatt charging deals with extremely high power and the need to protect both the vehicle and the charging station in the case of a fault. If the application has multiple battery packs each would have requirements similar to a light vehicle application and would need to manage its portion of the charging current. Eaton's Breaktor is ideal for individual battery packs and is resettable (can be brought back online) to minimize downtime.
At the MCS port location, you must protect for a full system fault which can be up to 70kA. This protection must be current limiting to protect the vehicle systems making it an ideal application for Eaton’s truck series EV fuses. These fuses can be used in parallel to create a scalable protection strategy covering the entire MCS current range.
