Impedance spectroscopy on DC-link capacitors in SiC and GaN inverters
Why the impedance curve matters more than a single capacitance value
SiC and GaN inverters combine steep switching edges, high DC-link voltages and compact layouts. A DC-link capacitor therefore has to deliver more than nominal capacitance: engineers need to understand ESR, ESL and resonance behaviour across the relevant frequency range.
A precision impedance analyser such as the Tonghui TH2851 makes these parameters visible. For recurring production or service tests, the Tonghui TH2848 or a Tonghui TH2830 LCR meter can be suitable test stations.
Typical engineering task
An engineering team is developing a compact 800 V traction inverter. During prototype tests, DC-link overshoot and additional heating appear around the capacitor bank. Instead of checking only the datasheet capacitance, the team measures impedance over the expected operating range: low frequencies for energy storage, mid frequencies for load and control transients, and high frequencies for switching edges and layout resonances.
- Evaluate ESR minimum and losses over temperature.
- Identify series resonance and parasitic ESL.
- Compare capacitor types and parallel banks.
- Derive incoming-inspection and requalification limits.
Practical setup
The sample is connected with short, reproducible leads. Open/short compensation reduces fixture influence. The impedance curve is then compared with layout simulation, thermal models and switching measurements. Comparing new, thermally stressed and electrically aged parts is especially useful.
What engineers learn from the curve
A low and controlled impedance curve in the target range supports a robust DC link. Shifted resonance or rising ESR can point to EMI issues, higher ripple current or local heating. The measurement therefore supports capacitor selection, parallelisation, PCB layout and quality checks.
Related products
For detailed laboratory analysis, use the Tonghui TH2851 precision impedance analyser. For recurring test stations, the Tonghui TH2848 and Tonghui TH2830 LCR meter are useful options.
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