Column: Electric Vehicles
through-hole mounting options and weighing 68g. Tis high power density (3400W/in3
) facilitates physical placement for optimal position
within the power architecture of the vehicle. Te package is designed to operate in both conduction and liquid-cooled systems, and has roughly equivalent thermal dissipation on the bottom and top side of the package, for further flexibility in mounting and cooling.
Figure 6: BCM6153 efficiency over output load current
(high to low conversion) to the most efficient voltage to distribute power. Te high-voltage array has advantages (energy density and charge time, compared to lower voltage arrays) but also drawbacks (not SELV) that make it desirable for EV applications but dangerous for distributing power to loads throughout the vehicle. Instead, implementing a power distribution system to the LV148 specification allows power to be distributed at a safe voltage (SELV) that is more easily maintained than the high voltage from the battery and would require less copper for lower current than if it had been distributed at the legacy 12V. Te BCM converter reflects the HV battery discharge characteristics
scaled by the K factor 1/8. Tis virtual battery powers the LV148- compatible distribution system as effectively as any physical 48V battery, but with the energy density and associated benefits of a high- voltage battery in the system. Vicor’s BCM6135 converter is isolated, providing the required
protection when interfacing a high-voltage source to SELV distribution, and has over 97% peak efficiency with over 96% efficiency when operating over 30% of rated current; see Figure 6. Capable of delivering up to 65A (over 3000W) of power
continuously, arrays of BCM6135 converters can create high-power conversion stages between HVDC and SELV voltage ranges. Te BCM6135 has an input range of 260-410V and a fixed ratio conversion of 1/8 to deliver an output compatible with 48V distribution. Te BCM6135 measures 61 x 35 x 7.5mm, with chassis-mount or
Extending 48V distribution While system power can originate from a 48V virtual battery, it still must be distributed throughout the vehicle to a broad range of subsystem loads with different power requirements and a mix of 48V and legacy 12V inputs. While the advantages of delivering power at 48V vs 12V are clear (higher efficiency and lighter cables), how this mix will change over time is not. As 12V is marginalised, the vehicle power architecture must be flexible enough to adapt to new subsystems whilst delivering optimised weight and cost of all the required cabling. Te ideal solution is to extend the 48V distribution as far as
physically possible, and convert to 12V for legacy needs only where and when needed. Since the LV148 specification’s operating range can be transformed to a 12V-distribution-compatible input with a 1/4 K factor conversion, a BCM converter offers maximum efficiency. Furthermore, since both voltages are SELV, isolation is not needed, and a non-isolated converter can be used to convert 48V to 12V throughout the system. Identical in all other facilities, a non-isolated BCM is called a “non-isolated bus converter module”, or NBM, offering all the benefits described earlier: fast transient response, low impedance and bidirectional operation; see Figure 8. Te NBM can be integrated ubiquitously in the vehicle – it is
physically small to augment existing legacy subsystems wherever they are placed yet minimally disruptive if removed for future system upgrades to native 48V subsystems. Vicor’s NBM2317 offers peak efficiency of over 97.5% when operating
at 30% higher rated current, and can deliver up to 60A (800W) of continuous power.
Other applications While both BCMs and NBMs are finding homes in EV power systems, any other system powered from a battery – from ultralight UAVs to autonomous factory robots and artificial-intelligence computing platforms at the edge – can take advantage of their transformative capabilities.
Figure 7: The Vicor chassis-mount BCM6135
Figure 8: The Vicor surface-mount NBM2317
16 March 2023
www.electronicsworld.com
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