IEEE Power Electronics Magazine - December 2021 - 50

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and 80% of the IGBT's loss at 100°C. GaN achieves
lower conduction losses at all temperature ranges.
In contrast to traditional industrial motor drives,
EV traction inverters require bidirectional power
transfer. During regenerative braking, the switches
are controlled to allow the same inverter to act as a
rectifier to save energy, while the motor acts as a generator,
thereby allowing power to flow back to the
battery pack. GaN transistors allow third quadrant
operation with the gate voltage turned on, and the
same low conduction losses mean that synchronous
rectification can be employed to keep losses very low
in regenerative mode. This is not possible with IGBTs,
and anti-paralleling freewheeling diodes handle the
reverse power flow with higher losses.
GaN not only offers lower conduction losses at all
output levels and frequency ranges but can also be
used at higher inverter frequencies with better efficiency.
Figure 3 compares the switching loss performance
between GaN and IGBT. As GaN transistors
have zero reverse recovery charge (Qrr), GaN has
only 30% turn-on loss of the IGBT.
For performance comparison, three type of tranAttracting
Tomorrow
sistors (GaN, SiC MOSFET, and Si IGBT) are used to
evaluate the loss and efficiency with a 150 kW-rated
power traction inverter with a 400 V battery system.
The switching frequency setting is at 10 kHz or
20 kHz for GaN.
The traction inverter's losses and efficiency simuPowerful
string inverters
need powerful fuses.
lation results at 150 kW are shown in Figure 4 using
the transistors listed in Table 1. The GaN-based traction
inverter, at both 10 kHz and 20 kHz frequencies,
is 55% more efficient because of lower conduction and
switching losses. At a 150 kW output, the IGBT solution
dissipates at 4,500W at 10 kHz, while the GaN
solution only dissipates at 1,993 W at double the frequency
(20 kHz). It is also important to mention that
GaN transistors allow the traction inverter to operate
with a switching frequency at 20 kHz or higher without
sacrificing performance. The higher switching
frequency is generally favourable because it results in
reduced THD of the motor current at high RPM, and a
higher upper limit for the current control loop bandwidth.
Also, the GaN-based solution allows a 3% average
efficiency improvement compared to IGBTs. This
not only increases the average efficiency but also widens
the high efficiency area at various speeds (RPM)
and torque (p.u.) on the EV's mission profile [1].
For an 800 V battery system, a hybrid three-level
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T-type configuration [2], which combines both 650 V
GaN transistors (S2 and S3) on the neutral branch
and 1200 V IGBTs (S1 and S4) on the main switch
shown in Figure 5 is promising. Test results show
that a hybrid traction inverter has around a 90% loss
reduction compared to an IGBT-based two-level traction
inverter.
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IEEE Power Electronics Magazine - December 2021

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - December 2021
