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Silicon Carbide Modules Unlock Higher Power Density in Motor Drives

Because SiC MOSFETs have a high dV/dt
rate, an inadequate common-mode transient
immunity (CMTI) rating can permit latch-
through between the logic and driver output,
causing hardware failure. The CGD12HBXMP
offers a high, 100-kV/μs CMTI rating, low
(<5 pF) isolation capacitance, and differen-
tial inputs for increased noise immunity.
The CGD12HBXMP also shares the same
footprint as the XM3 module, allowing for
a compact power core to be formed with six
Figure 4: The XM3 dual-power–core CAB450M12XM3 modules and their drivers
structure supports the gate drivers to integrated on the cold plate (Figure 4). This
enhance stability and ease introduction of then becomes a compact solution for easy Figure 6: The Melexis IMC-Hall sensor
a thermal path. integration into dual-inverter designs. avoids bulky ferromagnetic cores to
significantly reduce volume.
DC-LINK CAPACITOR
footprint with size reduction over the Reduction in parasitic inductance is a key
previous-generation CP3012. A balanced concern, and as mentioned earlier, it is partly tance at the terminals. Combined with the
coolant flow at a rate of 4 LPM across reduced by the vertically offset power termi- 6.7-nH inductance from the XM3 module, a
each of the six module positions results nals on the XM3 modules to simplify busbar total power-loop inductance of just 20 nH is
in an extremely low thermal resistance of design and lower power-loop inductance. This achieved, allowing for faster switching speeds
0.048°C/W per position or 0.008°C/W per cold concern is further addressed in the choice of to be used.
plate. The cooling system has been tested up the DC-link capacitor shown in Figure 5.
to 750-W power dissipation per switch with The capacitor footprint is one of the biggest THE CONTROLLER
the CAB450M12XM3. obstacles to increasing power density. Six off- The selection of the processor for the control-
the-shelf 100-µF cylindrical capacitors would ler board in this system needed to be based on
DRIVER STRENGTH normally be used to achieve the required ripple the following considerations:
Because the SiC MOSFETs in the converter current rating, occupying a 451-cm footprint • It should have enough processing “horse-
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module are capable of high-power perfor- and requiring a separate busbar. Wolfspeed power” to sample all inputs and make
mance, the driver must have adequate drive instead used a custom-designed DC-link control decisions.
strength — peak output current rating, or how capacitor (Figure 5) with a compact footprint • It should have a high-enough ADC count
much current is utilized to switch the devices of just 234 cm . It features integrated lami- to enable all the required system states to
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on and off — to sustain fast switching speeds. nated busing connected to the power terminals be measured for appropriate control and
A >10-A rating is recommended to ensure of the XM3 power modules on both sides of the monitoring.
high edge rates. And Wolfspeed’s cold plate, which reduces the parasitic induc- • It should have fast hardware interrupts to
CGD12HBXMP gate driver delivers. tance in the power loop and ensures a balanced respond to fault conditions.
The two-channel gate driver is protected current path for both sets of modules. Compo- • It must support standards-based commu-
against overcurrent and reverse polarity and nent count is reduced as well by eliminating nications critical for proper operation.
has on-board 2-W isolated power supplies separate busbar and hardware. The system’s controller board therefore
to support 80-kHz switching frequency. Its The custom capacitor is 600 μF at 900 V uses a dual-core, floating-point, 200-MHz,
user-configurable turn-on and turn-off gate with a peak voltage rating of 1,200 V. Because 32-bit DSP from Texas Instruments. The DSP
resistors enable switching loss optimization. the stray inductance of the capacitor and has enough ADC inputs to measure current,
The driver also features tunable overcurrent integrated busbar is critical to reduce voltage voltage, and temperature and offers commu-
detection with soft-shutdown, undervoltage spikes under the high di/dt rates common in nication support, including isolated CAN.
lockout, and anti-overlap of PWM inputs. fast-switching SiC inverters, the design was
It also offers a ~2-µs inception to extinguish validated with an impedance analyzer that CURRENT SENSORS
time to safely shut down under a short-circuit. measured 13-nH equivalent series induc- The dual inverter uses six current sensors at
the output terminals. With that number of
sensors in the system, any size reduction in
the sensor modules chosen quickly becomes
significant. Although COTS current sensor
modules are easily available, they can be
bulky. Moreover, some of the three-in-one
sensor modules on the market add con-
straints to the busing geometry. For the
CRD600DA12E-XM3 system, Wolfspeed
chose the DC-to-250-kHz Melexis MLX91208
Hall-effect sensor to provide a high-speed
analog output signal proportional to the
external horizontally applied flux density,
with a response time as low as 3 µs.
Figure 5: The custom DC-link capacitor (left) and a to-scale size comparison with six The sensor is packaged in an eight-pin
standard cylindrical caps SOIC and is small enough to be mounted onto

www.eetimes.eu | NOVEMBER 2021