Jinsong Dai, Senior Global Marketing Manager – Electrification, Sensata Technologies
Now that the latest Electric Vehicles (EVs) are exhibiting operational ranges satisfactory to the general public, the attention has shifted to battery charging times. These EVs are using the latest in wide-bandgap semiconductor solutions and power topologies, with system voltages often well over several hundred volts. EV charging systems are migrating rapidly in the direction of DC-based 50kW to 350kW power solutions, which can reduce charging times to under a half-hour.
The need to address the EV-using public’s charging-time desires must also be balanced with the need to maintain safety, performance, and reliability. The significantly increased power, voltage, and current levels being used in the latest EVs and their charging systems are presenting design challenges to the engineers involved. When it comes to DC fast charging, the challenges related to higher voltages and power levels present some electrical protection issues.
In addition to industry issues like compliance with Fast Charging standards, these challenges include addressing charging infrastructure issues such as thermal efficiency and heat management as well as protecting electrical systems from faults. Companies like Sensata Technologies focus on electrical protection for DC fast charging systems, because in order to shorten the charging time, many high-power chargers are migrating to power levels of 1,000V and 350kW, or higher.
This puts a great deal of pressure on the electrical protection components of the charging system, as the higher voltage levels and currents force the high-voltage components in the system, such as contactors and fuses, to keep up. One of the most obvious concerns in a high-voltage power circuit of any kind is that the higher voltages involved can easily generate an arc under the wrong conditions, requiring greater separation distances. In such situations, contactors and fuses employ techniques to increase the separation distance to quickly quench any arcs.
An uninterrupted arc can cause a contactor or a fuse to undergo extremely rapid catastrophic thermal failure, creating a fire hazard and potential explosion risk. Another potential failure state can occur when the contactor and fuse pair during the overcurrent condition. This is where the contactor begins to break a circuit but begins to dissipate some of the overcurrent within itself, preventing that current from being used to properly break the fuse connection. Again, the potential impact could be a catastrophic failure of the system. A solution such as Sensata’s disconnect operation, where both the contactor and fuse are paired to work together, helps prevent risks of that nature.
Addressing higher voltages
Using higher voltage and current levels in a power system can reduce charging times, but it also increases the safety risks as well as other system design challenges. Using high-voltage contactors to provide safe circuit continuity is a more optimal solution over fuses, which need to be deployed in tandem to protect the system in the face of a threatening short-circuit event. Legacy DC thermal-fuse tech addresses short-circuit situations by using a melted connection to break the circuit. The challenge with DC thermal fuses is that in overcurrent situations the current may not be high enough to melt the link, creating a dangerous delay in the protection response.
Such an overcurrent situation where there is insufficient energy to break the fuse creates a dangerousgray zone where current levels may overwhelm its ability to interrupt the load, never reaching the thermal point for the fuse to trigger. The risk of a time delay before a thermal fuse can be activated while exceeding the breaking capability of a contactor is eliminated with solutions like the GigaFuse, which helps bridge the gap between what contactors can do in normal operation, and when the fuse trips, providing both overcurrent and short-circuit protection.
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Figure 2: Solutions like Sensata’s GigaFuse helps bridge the circuit protection gap between contactors and fuses.(Source: Sensata Technologies)
Contactors and fuses are mission-critical components for DC fast charging systems. Contactors provide safe circuit continuity during normal charging, while fuses protect the charging system during hazardous short-circuit and overcurrent conditions. It is critical to have contactors and fuses that can work in tandem to ensure seamless protection for the chargers during normal operating and overcurrent conditions.
Next Gen Contactors and Fuses
The higher voltage and power charging levels in charging systems means that contactors also need to have a higher breaking capability and is leading to an increased demand for contactors rated to 1000V and 500A. Another demand for required functionality is for contactor bi-directionality, which enables EV battery charging from the grid and/or a V2G (vehicle-to-grid) system, allowing exploitation of grid intelligence in an energy exchange market.
Dynamic power allocation is another technology approach that can tailor the charging process to the actual demand, by combining or sharing power from multiple charging ports. The bidirectional functionality of contactors enables chargers to allocate the power dynamically by allowing the current flow either forward or backward. Sensata Technologies’ robust solution is hermetically sealed and filled with gas, providing the necessary energy to switch in a relatively small size compared to open-air contactors.
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Figure 3: Another demand for contactor functionality is bi-directionality, which enables EV battery charging from the grid and/or a V2G (vehicle-to-grid) system, allowing exploitation of grid intelligence in an energy exchange market. (Source: Sensata Technologies)
Sensata continues its leadership in sealed switching technologies with the introduction of high voltage fuse products. GigaFuse is the world’s only hermetically sealed electromechanical fuse designed for high voltage and high power fuse application requirements. The GiagFuse series includes fuse products with both passive and passive/active combinations. It significantly increases system efficiency, eliminates thermal aging, and provides design flexibility for electrical protection.
Another example of the latest circuit-protection solutions being made available to the marketplace is the PyroTactor, presented as the world’s first contactor with an integrated pyro fuse. Sensata’s GFC PyroTactor combines the function of high voltage fuses and contactors in a single device, eliminating the need to size each component separately. The bi-directional GFC Series can handle system voltages up to 1500V, with passive and active triggering, and significantly reduces resistance, installation time, complexity, and cost.
The public is demanding better and more efficient EVs that have longer ranges and charge in less time. The latest power system solutions can address these battery-charging demands, but only if the circuits involved operate at their highest potential. This is where advanced circuit-protection mechanisms can not only improve safety and reliability, but also performance and functionality. Using the latest solutions, like Sensata’s GigaFuse and PyroTactor, can pay out cascading benefits in any given charging system, especially those operating at high power levels.