Page 12 - PEN eBook October 2025

SEMICONDUCTORS

▶ Using a thermal impedance model, along with The transient thermal impedance curve obtained
the loss data of the power converter in the through simulations is shown in Figure 3. Then scatter
application extraction is performed and the fourth-order RC
parameters are fitted to obtain the thermal impedance
model. The thermal impedance of the chip remains
THERMAL IMPEDANCE relatively constant with regard to its loss, allowing the
MODEL CREATION average value to the thermal resistance to be used.

In this work, Zhang conducted simulations for the SiC
power modules driving a three-phase permanent-magnet
synchronous motor. Each phase comprised a half-bridge,
whereby eight SiC MOSFETs are placed in parallel to
increase the current level. An estimation of the conduction
and switching loss was made under the operating
conditions of a bus voltage of 800 V, a phase current
of 640 A, a switching frequency of 8 kHz, and a coolant
temperature of 45°C. The forward and reverse conduction
losses were dependent on the R DS(on) and V DS(rev) , respectively,
which are dependent on bias conditions as well as the
junction temperature. Switching losses included the turn-on Figure 3: Transient thermal impedance curve modeled for
and turn-off losses of the MOSFET, while ignoring the much power module (Source: Zhang, Y., 2024)
smaller reverse-recovery loss of the body diode.
The loss model for the three-phase inverter under
A fourth-order Foster model, as depicted in Figure 1, was SVPWM three-phase modulation along with the thermal
created to fit the thermal impedance from the SiC MOSFET impedance model is used to then obtain the junction Shaping the Next-generation of
chips to the negative-temperature-coefficient thermistor temperature of each bridge arm. The instantaneous
inside the module. In Figure 1, R and C (I = 1 to 4) maximum junction temperature change obtained from
thi
thi
represent the thermal resistance and capacitance of each this is illustrated in Figure 4. Renewable Energy Solutions
order, T the junction temperature, P the net power loss,
j
loss
and T the temperature at the test point. When the heat generated by the chip and the external
m
environment reach thermal equilibrium, the maximum As the transition to renewable energy accelerates, Complementing this ecosystem, Renesas power also
junction temperature in the switching cycle remains power electronics must deliver higher efficiency, enables energy storage systems (ESS) where GaN
essentially unchanged. To validate the model, a reduced size and greater reliability. With innovation and MOSFETs implement efficient, highly integrated
three-phase motor test bench was built and at the device and system level, Renesas is driving solutions by reducing losses, increasing system
infrared cameras were used to obtain this maximum this transformation with advanced Gallium Nitride lifetime and supporting bidirectional power flow.
temperature. This showed about a 5°C error to what (GaN) solutions that redefine how energy is Advanced battery management solutions with fixed
the model predicts, which can be calibrated out. harvested, converted and stored. firmware allow fast prototyping with pre-developed
BMS and fuel gauge firmware.
Figure 1: Fourth-order thermal impedance model topology for Creating a validated thermal impedance model for For solar energy, Renesas supports the next
the SiC power module (Source: Zhang, Y., 2024) the SiC inverter power module allows designers to generation of microinverters based on bidirectional From rooftop solar to residential storage and hybrid
check thermal performance under working conditions. GaN switches (BDS). Unlike conventional inverters, Renesas delivers a complete portfolio that
The output of the Foster model is the thermal Designs can be tweaked based on the output from back-to-back configurations, GaN BDS enable simplifies system design, lowers costs and enables a
impedance (Z ). A 3D CAD model was created using the such modeling. This can complement real-time compact single-stage DC-AC topologies such as the sustainable energy future.
th
structure of a power module that includes direct-bonded parameter monitoring, which would also include aging Dual-Active Bridge (DAB) based cycloverter. This
copper, solder, ceramic substrate, and baseplate using effects. innovation eliminates bulky intermediate stages,
parameters shown in Figure 2. The advanced meshing reduces component count, increases power density
tool in Icepak software was used to create meshing. and improves thermal performance.
These layer details are obtained through the disassembly
of an actual power module sample. In parallel, Renesas offers hybrid inverter solutions
using high-performance GaN FETs. These devices
support both grid-tied and off-grid operation
with superior switching performance to enable
seamless integration of solar and battery power
while maintaining high efficiency under varying load
conditions.

Figure 2: Thermal parameters of the power module Figure 4: Maximum junction temperature change curve
components (Source: Zhang, Y., 2024) (Source: Zhang, Y., 2024)

12 OCTOBER 2025 | www.powerelectronicsnews.com