IEEE Power Electronics Magazine - June 2019 - 55

is substantially different from those for which the battery
of tests was designed, so there remains a risk that these
differences may cause the new design to fail from a process that was not accelerated or not accelerated as much
by the test protocol. What was most significant about
this paper was the commitment it shows to proceeding
to production and the willingness of the company (with
a well-earned reputation for conservativism) to innovate
to this extent in this case. Later, several presenters at an
industry session devoted to advanced packing mentioned
a number of developments in the direction of higher reliability, but none of these reports had the depth of detail
or the specificity of the examples cited above.
Prof. Nihal Kularatna of the University of Waikato
in New Zealand presented another thought-provoking
paper "DC-UPS Capability for the SCALDO-Assisted 48-V
Google Rack Power Architecture." The acronym stands
for supercapacitor-assisted low-dropout regulator. The
basic premise of the converter involves inserting a supercapacitor upstream of a linear regulator stage. The insertion of the supercapacitor can be modulated at very low
frequency in such a way that almost all of the voltage drop
between input and output appears across the supercapacitor, leaving a very low voltage drop across the dissipative
linear regulator. This is a clever idea in itself, although
the paper does not make a compelling economic case for
this notion in this application. But by enabling the supercapacitor to additionally serve as the source for uninterruptable power supply operation, essentially a short-term
protection against loss of mains power, this paper offers
a potentially attractive alternative to electrochemical

energy storage for this function, with the potential for
superior overall value.
Gorkem Secer presented a paper "Parameter Estimation of Permanent Magnet Synchronous Machines Based on
a New Model Considering Discretization Effects of Digital
Controllers." The work acknowledges financial support from
Roketsan Missile Industries Inc., which is a Turkish munitions
manufacturer, and it deals with a problem with digitally implemented field-oriented control of surface-mount permanent
magnet motors. One can be forgiven for thinking that, after
all this time, this technology would be completely mature,
but the paper and the presenter made a strong case that there
remains room for improvement. The finding is worthy of note,
and the paper serves as a warning not to judge a technical
paper based on its origin rather than its content, and as a testament to the power of even a late adopter to advance technology by thinking clearly and with independent judgment.
A paper titled "Series ac Arc Fault Detection Using
Only Voltage Waveforms" was presented by a team from
Northeastern University in Boston and Mersen USA in
Newburyport, Massachusetts. This is an important and difficult problem. The authors chose an approach that seems
to offer excellent results, with a good possibility for use in
practical systems. They do need to digitize a voltage signal
at a relatively high frequency, but that should be economically within present-day capabilities. But the data processing and decision-making processes are reassuringly simple.
Essentially, they rely on the long-known fact that an ac arc
extinguishes in the vicinity of current zero and reignites
afterward. Signal processing consists of a bandpass filter,
a squaring of the output, and a few simple comparisons of

Solder Fatigue Failures-Eliminated
Conventional DBC Ceramic Module
Wire

Chip

Base Plate Solder Layers Ceramic Substrate

Mitsubishi SLC Package
DP Resin
(Lidless)

IMB (Resin Insulation)

Chip

PC-TIM

Solder Layer

Insulation Substrate
Crack

Solderless Bond With Matching
CTE-Solder Fatigue Eliminated

Copper Base Plate
Solder Fatigue-Caused By Thermal Cycling With
CTE Mismatch Between Ceramic and Copper
FIG 5 A cross section of a new IGBT package, with solder joint eliminated. Note the continued presence of another solder joint
and wire bonds. CTE: coefficient of thermal expansion; DBC: direct bonded copper; SLC: solid cover; IMB: insulated metal baseplate; PC-TIM: phase change-thermal interface material. (Source: Mitsubishi Electric; used with permission.)

June 2019

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IEEE Power Electronics Magazine - June 2019

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - June 2019
