Page 25 - EE Times Europe November 2021 final

EE|Times EUROPE 25

Silicon Carbide Modules Unlock Higher Power Density in Motor Drives

turn-on switching energy of 23.1 mJ at 800 V and 600 A, with a peak
current overshoot of 113 A. The turn-off switching energy was
30.1 mJ. The margin of the bus voltage for the die was 80 V, a 2×
overload condition compared with the nominal rating of the module.
Next, switching losses per module were calculated from the known
turn-on energy of 12.2 mJ and turn-off energy of 12 mJ at the 300-A
nominal condition. Using the formula for switching power loss (P ),
sw

and plugging in E and a switching frequency (f ) of 10 kHz,
on SW

this loss is 3× lower than for a comparable Si IGBT (HybridPack 1,200
V, 380 A nominal), with SiC having the big advantage of an extremely
low reverse-recovery energy (E ).
rr
The design was also validated under application conditions using
a three-phase recirculating load test. The design’s flexible output-
terminal arrangement eased test setup: The six outputs can be
utilized either as two independent three-phase inverters delivering
375 A rms each or, with the addition of a simple busbar and parallel-
ing of phases, as a single three-phase inverter capable of 750 A rms
(Figure 7).
For the test, the single-inverter setup was used with AC outputs
U and X combined to form Phase A, V and Y to form Phase B, and W
and Z to form Phase C. Three 125-µH load inductors were connected
between one of the output terminals of the inverter and the midpoint
of a large capacitor bank — 2.2 mF per half — rated to 1,100 V. This
enables high-power testing with only a few kilowatts of power
supplied and with the DC voltage source only supplying the system
losses. Energy is transferred from one half of the capacitors to the
other half through the inductors during each switching cycle, and the
direction of energy transfer is reversed over one cycle of fundamen-
tal frequency.
After a five-minute test at 800-V bus voltage, the capacitor case
reached 13°C above ambient, while the gate driver hot spot mea-
sured 40°C above ambient. For a switching frequency of 10 kHz and
a fundamental frequency of 300 Hz, the RMS paralleled output cur-
rent was 750 A, equivalent to 624 kW of output power. The current
ripple with the chosen load inductor was 160 A at 10 kHz, while the
peak combined current reached 1,200 A, including the current rip-
ple. The switching energy at 10 kHz, 375 A was 31 mJ. For the total
losses of 5.53 kW or 460 W per switch, the switching losses were
1.8 kW. This results in an efficiency exceeding 99% for the inverter
up to 624 kW (Figure 8).

THE FINAL WORD
Meeting the five key design considerations set out earlier, the
CRD600DA12E-XM3 three-phase dual-inverter reference design
utilizes the CAB450M12XM3 power modules to achieve a peak output
power of 624 kW and a current rating of 375 A per phase or 750
rms
A paralleled. In the full-metal 204 × 267.5 × 157.5-mm enclosure
rms
(shown in Figure 1), this solution weighs 9.7 kg and occupies merely
8.6 L in volume to reach the exceptionally high power density of
72.5 kW/L. This is more than double that achieved by the previous
300-kW SiC reference design and 3.6× better than what is possible
with an equivalent-rated IGBT-based inverter (Table 1). ■
For more about the CRD600DA12E-XM3 three-phase dual-inverter
reference design, the CAB450M12XM3 power module, and the CGD12H-
BXMP gate driver, go to www.wolfspeed.com/eetimes-refdesign.

www.eetimes.eu | NOVEMBER 2021