10 CONDUCTED EMISSION COMPLIANCE www.vicorpower.com Issue 3 2024 Power Electronics Europe www.power-mag.com behaves like an inductor. Solving high-frequency power conversion With decades of industry-leading experience in power electronics design, Vicor has developed DC-DC conversion solutions that harness all the benefits of high-frequency conversion without the negative side effects. Specifically, the Vicor NBM™ family of non-isolated bus converter modules successfully switch at frequencies above 1.3MHz. With respect to efficiency, the NBM™ line of products can realize minimal power losses at high frequency by using zero voltage switching (ZVS) and zero current switching (ZCS) technology. Zero-voltage switching works by carefully timing the switch’s operation so that the switching aligns with the moments when the voltage across the switch is zero. Similarly, zerocurrent switching works by timing the switch’s operation so that it coincides with the moments when the current through the switch is zero. (Figure 3) Vicor ZVS and ZCS are achieved by introducing a separate phase to the pulsewidth modulation (PWM) timing. Utilizing the added phase, the solutions use a clamp switch and circuit resonance to efficiently operate the high side and synchronous MOSFETs with soft switching, avoiding losses incurred during conventional PWM hard switching operation and timing. Thanks to ZVS and ZCS, products like the NBM line of DC-DC converters can operate at 1.5 to 1.7 MHz while still achieving peak efficiencies of up to 99%. The combination of high switching frequencies and efficiency enables solutions with unparalleled power density, up to 550 kW / liter. In terms of EMC, the NBM™ products can achieve compliance, even at unusually high frequencies. In a recent set of tests, conducted emission compliance of the NBM9280 power module was evaluated. This Vicor module is capable of converting 37.5kW, with a power density of 550 kW/ liter, for electrified vehicle applications. The testing found that, even at a switching frequency of 1.3MHz, the NBM9280 could satisfy CISPR32 limits with a combination of Pi filtering and introducing a ferrite core around the input power cables. (Figure 4) The resulting filtering components were significantly smaller than what is necessary for a lower-frequency (i.e., 100kHz) solution, yet the same compliance was achieved. All things considered, automotive designers can simply replace their existing DC-DC conversion systems with the NBM™ line of products and immediately realize the benefits of smaller size and greater power density without risk of compliance failure or efficiency losses. Higher frequency supports today’s EV demand period. With a shift to EVs the automotive industry is demanding smaller, lighter and more power-dense solutions which can support vehicle to grid interfaces. For power electronics designers, a switch to higherfrequency DC-DC conversion solutions is an ideal way to meet these demands. Vicor has been able to develop DC-DC conversion solutions that operate with switching frequencies as high as 1.74MHz without incurring the conventional shortcomings of high switching frequencies. With products like the NBM™ family of DC-DC converters, automotive designers can realize a future where vehicles are efficient, lightweight and high performing, without the design complexity or expertise that often accompany these results. ! Figure 4: The NBM9280 passed conducted emission compliance with the addition of a dedicated PI filter.
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