IEEE Electrification - June 2022 - 62

The third technique involves using
an intelligent gate drive to minimize
the switching loss of SiC power
devices. As illustrated in Figure 4, in
the baseline design, 17% of the total
loss of the inverter comes from the
device's switching loss. The intelligent
gate drive increases the switching
speed of the devices without
causing crosstalk and can reduce
the switching loss by 20% when
compared to the conventional gate
drive, resulting in a 3% total loss
reduction.
The fourth technique is to adopt variable switching freOne
particularly
promising technology
for future hydrogen-
electric aviation
applications relates
to cryogenic power
electronics.
quency (VSF) pulsewidth modulation (PWM) schemes to
attenuate EMI noise and minimize switching loss. One VSF
PWM scheme adjusts the switching frequency to control
the ac current ripple peak so that it is constant below its
threshold. This can lead to a 14% switching loss reduction
as compared to the constant switching frequency PWM in
the baseline design, which enables a 2.4% total loss reduction
of the inverter. Furthermore, with the same VSF PWM,
the EMI noise peak can be suppressed, and an approximately
10-dB reduction of the conducted EMI noise peak
can be achieved, per DO-160 EMI standards. Thanks to the
EMI noise attenuation, the required attenuation of the EMI
filter decreases, enabling the bulky magnetic components
of the EMI filter to be significantly reduced in size. As a
result, the weights of the dc-side common mode (CM)
choke, ac-side CM choke, and ac-side differential mode
(DM) inductor are reduced by 7, 12, and 71% respectively.
In the end, the total EMI filter weight is 73% of that in the
baseline design. Also, due to less winding and smaller
cores in the CM choke and DM inductors, lower losses will
result, leading to an EMI filter loss reduction of 30%.
The fifth technique employs ad -
vanced EMI filtering strategies. The
dc CM filter can be realized by constructing
the bus bar as a filter, based
on the transmission line theory. This
type of filter structure utilizes the dc
bus bar of the inverter as the winding
of the dc CM choke, thus eliminating
the extra winding weight. The bus
bar design adopts a standard multilayer
structure, which, together with
ex ternal magnetic cores, can greatly
enhance the dc CM inductance. The
CM capacitance is also provided with
high-permittivity insulation layers. The bus bar filter
enables a reduction of the total EMI filter weight by 14%.
By adopting hybrid ac and dc filters with an extra 30-dB of
attenuation, the weight of the ac CM choke can be
reduced by a factor of four. Note that the negative impact
of the active filter induces extra loss, causing a 9%
increase of the total loss of the inverter system in this
benchmark design.
Combining all the aforementioned techniques and
their resultant influence on power loss and weight, the
efficiency of the 1-MW inverter operating at 500 kW is
99.07%, which exceeds the 99% target efficiency. Additionally,
the specific power is improved to 18.1 kW/kg, which
approaches the 19-kW/kg target in Table 1. Figure 6 presents
the evolution of power loss and weight reduction
when different approaches are employed. Additional
methods, such as additive manufacturing, can be applied
in mechanical, filter, and thermal designs to further
reduce weight. It should be pointed out that the GE inverter
(Zhang et al. 2019) did not adopt all the high-density
techniques described here. Its high specific power and
power density resulted from the fact that it did not have
Unit: Grams
Unit: Grams
4,000
18,742
37,100.4
EMI Filter
(77%)
64,233
Power Devices
dc CM Choke
ac CM Choke
ac DM Inductor
dc and ac Capacitor
Specific Power: 6.2 kW/kg
Target Specific Power: 19 kW/kg
dc Link capacitors
dc Bus Bar
Cold Plate
Gate Driver, Sensors,
and Interface Board
Inverter
(13%)
5,832
9,000
Housing
(10%)
2,594
1,080 1,890
Figure 5. The weight breakdown and specific power based on the baseline design of the 1-MW inverter.
62
IEEE Electrification Magazine / JUNE 2022

IEEE Electrification - June 2022

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