12 HIGH-VOLTAGE-TO-48V POWER CONVERSION www.vicorpower.com/ Issue 2 2024 Power Electronics Europe www.power-mag.com 11 ways to fine tune your high-voltage-to-48V power conversion Today’s new and existing electrification applications in the industrial, automotive, data center and defense sectors require more power. They are driving the need for higher voltages and conversion to lower DC SELV (safety extra-low voltage) levels – defined as below 50VDC. Often SELV level is 48VDC or 28VDC . High-voltage-to-SELV applications High voltage (HV) DC applications include 400V or 800V electric vehicle battery packs, AI data center 400V or 800V distribution to racks, with both electrical system architectures often converting to 48V. These principal HV-to-SELV use cases have created an ecosystem of components such as DC-DC converters, competence and know-how, and successful system design and deployment.[j1]Other HV to SELV application examples include solar and fuel cell power generation, longdistance subsea cables, large industrial robots, medical imaging systems, shipboard and aircraft power distribution, semiconductor ion implantation equipment. Telecom equipment has used -48VDC battery backup for decades, derived from 300VDC rectified from 220VAC from the utility grid. Thinner, lighter 48V cabling lowers thermal power losses Unlike AC transmission systems such as utility grids, DC transmission systems do not have an electrically reactive (capacitive and inductive) component and are thus generally more efficient. DC distribution is purely resistive. (AC distribution also experiences resistive losses.) High-voltage cables have lower conductive thermal losses (I2R), are thinner and lighter and use less copper, an expensive commodity base metal due to the explosion of AI data centers among other factors. For example, to carry the same level of power, a 12V cable needs to carry 64x more current than an 800V cable. The 12V cable might use a 2 AWG copper conductor (approximately $20 per meter) while the 800V cable might use a 22 AWG copper conductor (approximately $0.30 per meter), which is obviously a substantial cost difference for long cable runs. Furthermore, the weight difference between 2 AWG cable and 22 AWG cable is about 0.2kg per meter. These key factors are driving the increasing adoption of DC power delivery, particularly in platforms in which are weight and cost sensitive. Resistive thermal dissipation in the cables used for high-power distribution can also be a major OPEX consideration beyond the CAPEX savings described above. Due to the extremely high power levels in AI data centers in the assessment of the Power Usage Effectiveness (PUE) of AI data centers, for example, approximately 6% of the incoming AC grid power is Figure 1: A light electric vehicle’s power delivery network converts a high-voltage battery source to a 48V bus using a fixed-ratio DC-DC Bus Converter Module (BCM).[j2] Figure 2: High-voltage cabling provides not only low cost, but also higher efficiency and critical weight savings for products that require longer runtime. All other electrical parameters assumed equal (specifically cable resistance), 12V cabling dissipates 16x the losses of 48V cabling while delivering the same power to the load. By Maury Wood, VP Strategic Marketing at Vicor
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