Capacitors and SiC stack combine in high power density SiC inverters

High temperature semiconductor and power module supplier, Cissoid, has collaborated with component specialist, NAC and capacitor company, Advanced Conversion to develop a compact and optimally integrated three-phase SiC power stack. It combines a 1200V SiC intelligent power module (IPM) from Cissoid and a six-pack low-ESR / ESL DC-link capacitor from Advanced Conversion. 

The power stack can be further integrated with a controller board and a liquid cooler to design of high power density and high efficiency SiC inverters for e-motor drives. 

Cissoid’s IPM integrates a three-phase 1200V / 340 to 550A SiC MOSFET power module with a temperature-robust gate driver enabling low switching losses and high power density, said the company. A control board and algorithms provide real-time processing, control and functional safety for SiC inverters in e-motor drives. The power module’s on resistance ranges from 2.53 to 4.19 mOhms depending on current rating. The total switching energies are as low as 7.48mJ (Eon) and 7.39mJ (Eoff) at 600V / 300A. 

The co-design of the power module and the gate driver enables optimising the IPMs for lowest switching energies by carefully tuning dV/dt and controlling voltage overshoots inherent to fast switching. The embedded gate driver solves multiple challenges related to fast-switching SiC transistors, negative drive and active Miller clamping (AMC) prevent parasitic turn-on. There is also desaturation detection and soft-shut-down (SSD) and under-voltage lockout (UVLO) functions on gate driver and DC bus voltages to monitor the proper operation of the system. 

The six-pack DC-link capacitor from Advanced Conversion mechanically fits to Cissoid IPMs through a low inductance bus bar. A set of capacitor values, up to 500 microF, and of voltage ratings, up to 900V, is available for rapid evaluation. 

Custom designs are also available, based on Advanced Conversion’s annular form factor film capacitor that is suited for surface mounting to an optimised bus structure that interfaces with the switch modules. This patented approach combined with bus cooling provides a very high Ampere per micro-Farad rating to allow the smallest possible capacitance while simultaneously minimising the commutation loop inductance. Equivalent series inductance values of less than 5nH are readily achieved using the right switch module with an appropriate connection design.

“The DC link is a critical component for high power inverters using fast switching that is often overlooked during the initial stages of design,” said James Charlton, director of product marketing, NAC. Efficient fast switching wide bandgap devices require a carefully designed DC link bus topology with tightly integrated capacitors, he explained. The capacitor kit allows customers to find a capacitor suited to Cissoid’s fast-switching three-phase SiC IPMs, accelerating their inverter design for compact and efficient e-motor drives, added Pierre Delatte, CTO of Cissoid.

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