www.vicorpower.com AUTOMOTIVE POWER 11 www.power-mag.com Issue 1 2024 Power Electronics Europe battery packs needs to be accessible on the high voltage connector. An imbalance of two series connected 400V battery packs may cause the regulator to enter in an overvoltage protection mode condition, interrupting the power supply period. The advantages of the system are: If one string fails, the other string will pick up the load. The components of the system have lower voltage ratings and are therefore less expensive. It is easier to create a 24V output by connecting the two outputs in series. The Dual-800V parallel battery configuration also has some tradeoffs. Advantages It operates with more stability than using 400V period. It is easier to charge, as the parallel combination will see the entire 800V source. In a parallel combination the packs are always at equal voltages. This makes it less complicated to charge. Disadvantages: From a design perspective, the components do need more clearance to the chassis for high voltage safety. A short across the 800V will potentially shut down the entire system. While relatively few vehicles currently utilize a dual 800V battery platform, the redundancy that it offers is important for safety. Without it, the most important car systems are one short away from a catastrophic event. EV power architectures are moving in this direction. Reliability and safety are the biggest reasons for the migration, but newer chargers are compatible with both 400V and 800V, which illustrates further market pull toward 800V. Different factors may preclude choosing one approach over another, but in most cases the Dual-800V battery configuration is preferred for one simple reason. In this system, the power modules make it easy to build in redundancy by using the batteries in parallel. This enables a second power path to the load in the event of a short, protecting the system from total shut down. There are weight and range considerations in addition to the demand on physical space to accommodate two battery packs. While some additional circuitry is required for the battery management system, the safety and reliability benefits outweigh that in the big picture. The many faces of power redundancy—which is best? Implementing redundancy can be done in a number of ways (Figure 3). The load can be shared across two or more DC-DC converters, with the ability of a single converter to take up the entire load should one of the power sources or converters fail. Redundancy can take several forms. Look at the entire power chain from the source to the load and ask; If there would be a failure at this location or portion of the circuitry, What would be impacted? Will the vehicle still drive? What functions will not work? The objective is to be able to continue the driving journey or be able to safely exit the highway off-ramp. Redundancy in a DC-DC converter can take many forms (Figure 3). Some examples are N + 0, N +1, 2N + 1, etc. Each configuration has advantages and disadvantages in terms of size, cost and complexity. A careful study needs to be performed for each vehicle’s architecture. By using a bidirectional DC-DC converter and separating the loads of the vehicle, power can be passed from one zone to the other. Passing the power through a regulator provides a solid source to power the load or even charge a battery. However, today’s current converter technology is not capable of making DCDC converters that are small and light enough to use multiple units in parallel in BEVs. The Vicor BCM® and DCM™ power modules enable easy paralleling. Their Figure 2 — Dual-800V parallel battery configuration. This configuration, allows for lower-current operation and an easier method of implementing an N + 1 redundancy (Source: Vicor) Figure 3 — Several combinations of redundant architectures show power levels and power split in an EV powertrain. The N + 1 has more power capability and therefore can be a larger and more expensive solution. From left to right, the redundancy improves and the power supply more closely matches the load’s requirement, but it also increases component count and system complexity. (Source: Vicor)
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