IEEE Power Electronics Magazine - December 2020 - 18

reducing losses due to the reduction in ac impedance
from 10 to ~1 Ω. The peak current dropped to 9.75 A with
a small output LC filter - above the converter's 8.75 A
continuous current limit but well within the 14 A short
term current limit.

on highly-efficient, non-isolated end power stages that have
a moderately wide input range. These can be connected to
higher-voltage battery architectures through fixed-ratio converters deployed with appropriate transfer ratios.

About the Authors
Capacitive Loads
At startup, motor drives and computing boards act as large
capacitive loads. Computing cards may have a large array of
onboard buck converters, each equipped with bulk input
capacitors, and/or additional LC filters. The DC-DC converter powering them needs to have either a generously
specified allowable external load capacitance or to be followed by a form of pre-charge circuit to work with large
capacitive loads as is often the case powering motor drives
with fixed-ratio converters.
This is an often-overlooked item until late in the design.
Some regulators, particularly buck-boosts, are also designed
for battery charging and allow for a separate current-control
loop and/or adjustable soft-start time, allowing for them to
be used with massive load capacitances.

Anna Giasson is an applications engineer at Vicor Corp.,
Andover, MA, USA. She has designed switched-mode AC-DC
power supplies with active PFC. She is obtaining her Master's degree in Electrical and Electronics Engineering from
Worcester Polytechnic Institute and has a Bachelor's degree
in Electrical and Electronics Engineering from Wentworth
Institute of Technology in 2015
Stavros " Steve " Dokopoulos is a field applications
engineer at Vicor Corp., Richmond, Virginia, USA. He obtained
his Master's degree in Electrical and Electronics Engineering
from Aristotle University of Thessaloniki, Greece, in 1989
and has worked in the power electronics industry since.

References
[1] D. Jauregui, B. Wang, and R. Chen, " Power loss calculation with common
source inductance consideration for synchronous buck converters, " Texas

Power Regeneration and Input Voltage Considerations

Instruments, Application Rep., July 2011. [Online]. Available: www.ti.com/lit/

During dynamic operation or braking, a motor drive may act
as a generator (8). In our 57 V example, the regenerating primary motor drive's reversing current will charge the battery
through the connecting harness, raising its voltage along the
path proportionally to the associated impedances, possibly
to above 60 V. Any DC/DC converter powered by it would
then have to be rated not at the commonly available 60 V
but to a higher voltage.
The schematic in Figure 6 also applies to power distribution networks where a motor drive is powered by a bidirectional converter, as our example in Figure 8. Regenerating energy can raise the voltage on both the low voltage
and high voltage terminals proportional to ZOUT through the
converter. If the converter is unidirectional this regenerative energy is blocked and only the output capacitor COUT is
charged. So the regenerative energy and its resulting voltage rises should be limited if possible to stay within the
maximum output voltage specification of the converters
and COUT, or a brake-circuit can be implemented to absorb
the energy.

an/slpa009a/slpa009a.pdf
[2] P. Yeaman and E. Oliveira, " A high efficiency high density voltage
regulator design providing VR 12.0 compliant power to a microprocessor directly from a 48V input, " in Proc. IEEE Applied Power Electron.
Conf. Expo. (APEC), 2013. [Online]. Available: https://ieeexplore.ieee.org/
document/6520241
[3] M. Ursino, S. Saggini, S. Jiang, and C. Nan, " High density 48V-to-PoL
VRM with hybrid pre-regulator and fixed-ratio buck, " in Proc. IEEE Applied
Power Electron. Conf. Expo. (APEC), 2020. [Online]. Available: https://
ieeexplore.ieee.org/document/9124561/references#references. doi: 10.1109/
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[4] S. Taranovich, " What's the difference between fixed-ratio, regulated, and
semi-regulated IBC? " Electronic Design, Dec.10, 2019. [Online]. Available:
https://www.electronicdesign.com/power-management/power-delivery/
whitepaper/21808958/whats-the-difference-between-fixedratio-regulated
-and-semiregulated-ibcs
[5] E.-S. Kim, J.-H. Park, J.-S. Joo, S.-M. Lee, K. Kim, and Y.-S. Kong, " Bidirectional DC-DC converter using secondary LLC resonant tank, " in Proc.
IEEE Applied Power Electron. Conf. Expo. (APEC), 2015. [Online].
Available: https://ieeexplore.ieee.org/document/7104639. doi: 10.1109/
APEC.2015.7104639.

Summary

[6] D. Bourner, " Reverse mode application of sine amplitude converters, " in

In any robotic system, ranging from mobile platforms to distributed static stations, designers are encouraged to map
out the power tree of their application and weigh different
types of converter combinations and PDN design strategies.
It is advantageous to distribute a higher voltage across a
platform and transform it close to point of load to the
required voltage.
Creative use of fixed-ratio converters combined with Buck
and/or Buck-Boost regulators likely will achieve optimal performance for each load with efficient and lightweight power
delivery. Combining these makes it possible to standardize

Proc. PCIM Europe, May 10-12, 2016. [Online]. Available: https://ieeexplore

IEEE POWER ELECTRONICS MAGAZINE

z December 2020

.ieee.org/document/7499574
[7] M. Salato and P. Makrum, " Yeaman topology power system, " in Proc.
Int. Conf. Energy Aware Comput., 2010. [Online]. Available: https://
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ICEAC.2010.5702276.
[8] Y. Wei, Y. Xu, J. Zou, and Y. Li, " Current limit strategy for BLDC motor
drive with minimized DC-link capacitor, " IEEE Trans. Ind. Appl., vol. 51, no.
5, pp. 3907-3913, Sept.-Oct. 2015. [Online]. Available: https://ieeexplore.ieee
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IEEE Power Electronics Magazine - December 2020

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