IEEE Power Electronics Magazine - September 2022 - 21

Power Source
Variable frequency drive
+
-
Motor
M
ICM
Parasitic
capacitance
Common GND
200
100
-100
-200
11 111 11 11
0.4
0.2
-0.2
-0.4
0.1
offset=0
0.15 0.2
0.25
0.3
Times (ms)
FIG 7 Common mode voltage and current in a typical motor drive.
0.35
0.4 0.45
offset=0
Higher Switching
Speeds & frequency
Si to WBG
Devices
200
100
-100
-200
0.0001 0.00015 11111 111
0.2
-0.2
-0.4
0.1 0.15 0.2 0.25 0.3
Times (ms)
0.35 0.4 0.45
Higher
Common mode voltage at the neutral point of the three-phase motor and resulting common mode current.
the power converter and power source. When Si devices
are replaced by SiC or GaN devices, the rising edges of the
common mode voltage will become sharper, with similar
layout of the power electronics and electric machine structure,
the peak value of the common mode current will
increase due to the higher switching speed. If higher
switching frequencies are implemented, the repeating frequency
of the common mode current pulses will also
increase [30], [31].
However, on the bright side, the
fundamental frequency of typical
electric machines for MEA and
future electric propulsion are usually
in the range of few hundred of
Hertz to couple kiloHertz. Though
potential
implementations of perThe
Si inverter was controlled to switch at 30 kHz and the
SiC inverter was controlled to switch at 30 kHz and then
60 kHz. As shown in Figure 8, the measured conducted
EMI for SiC and Si inverter are similar when both were
switching at 30 kHz. It was pointed out that the tested SiC
inverter will need EMI filters to pass MIL-STD-461 part
CE102, the size of the required filter will be similar to the
size of the filter that is required by its Si counterpart [31].
manent magnet machines will result
in lower leakage inductance, which
requires higher switching frequency
to achieve reasonable power quality,
the switching frequency of SiCbased
machine drives will most
possibly stay below 60 kHz, which does not significantly
change the conductive EMI spectrum [31]. A recent study
compared the EMI performance of commercial-off-theshelf
(COTS) 250-kW SiC MOSFET-based inverter and a
250-kW Si IGBT-based inverter with similar construction.
With WBG devices,
partial discharge
becomes a more pressing
issue because of
the higher switching
speed.
Design and Product Examples
In the last few years, there have been
great design examples of WBG-based
power converters and motor drives
for aerospace applications. Figure 9
shows a 600 W GaN-based noninverting
buck-boost (NIBB) converter
designed for photovoltaic panels in
space applications. The converter has
integrated maximum power point
tracking (MPPT) function and has
been tested at -140 °C successfully.
The measured efficiency of the converter
at -110 °C is 98.31%. The specific power of the converter
is 3.76 W/g [32].
In Figure 10, a 10-level 18.9 kW flying capacitor multilevel
inverter module is shown. The module is based
on 150 V GaN devices and achieves 98.95% efficiency,
September 2022 z IEEE POWER ELECTRONICS MAGAZINE 21
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IEEE Power Electronics Magazine - September 2022

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