Device for Measuring Commutation Currents in Fast-Switching Semiconductor Components

The patented technology combines tunnel magnetoresistive sensors with a Rogowski coil in a coaxial current-measurement device. It enables precise, galvanically isolated measurement of commutation currents over a broad frequency range (DC to 50 MHz) with minimal insertion inductance of only 1 nH and a compact form factor.

•  Extremely low insertion inductance (approximately 1 nH)
• Broad frequency range from DC to 50 MHz
• Galvanically isolated measurement without a reference potential
• Compact form factor (approximately 2 cm diameter)
• Enhanced bandwidth through TMR sensors using the HOKA method

The innovative current measurement device can be primarily used to develop and characterize modern power semiconductors made from SiC and GaN. It enables precise optimization of high-frequency power electronic circuits and supports quality assurance in the manufacturing of power modules. In research, it contributes to the development of new circuit topologies and enables accurate fault diagnosis in energy conversion systems. It is particularly valuable for measurement technology in inverters for electric vehicles and renewable energy systems, where precise acquisition of commutation currents is crucial to improving efficiency.

Advances in power electronics, driven by electromobility, renewable energy, and Industry 4.0, are placing new demands on measurement technology. Modern semiconductor materials such as SiC and GaN enable increasingly faster switching operations with slew rates in the nanosecond range.

These advances lead to higher switching frequencies and greater efficiency but require precise measurement methods to characterize power semiconductors and optimize gate drive concepts. Reliable acquisition of commutation currents is critical. While solutions to this measurement challenge are being sought, galvanically isolated measurement methods with sufficient bandwidth remain an unsolved problem.

Commutation currents in power electronic circuits require sensors with a frequency range from DC to 50 MHz. Currently, only the coaxial shunt is available, which requires a reference potential. With dynamic potential changes, an isolation transformer must be used, but its parasitic winding capacitances distort the measurement during fast voltage transients—a significant limitation for precise characterization of modern power electronics.

The team at the Institute for Power Electronics and Electrical Drives (ILEA) at the University of Stuttgart has developed a new measurement device that precisely captures commutation currents in power electronic circuits. The device consists of an inner conductor and an outer conductor arranged coaxially, with the outer conductor forming a coaxial chamber around the inner conductor. Two sensor arrangements are integrated within this chamber: four circularly arranged tunnel magnetoresistive (TMR) sensors for measuring the low-frequency current component and a toroidal Rogowski coil for capturing the high-frequency current component. The measurement device explicitly uses the HOKA method for signal evaluation. The measurement signals from both sensor systems are summed and passed through a low-pass filter. This construction enables a bandwidth from DC to 50 MHz, with an insertion inductance of only 1 nH and a compact form factor of just 2 cm in diameter. The compact design (2 cm diameter) and high measurement accuracy, together with SiC and GaN power semiconductors featuring steep switching edges of up to 4 A/ns, make this technology particularly valuable for optimizing modern energy conversion systems.

N. Tröster, "Erfassung von hochdynamischen Kommutierungsströmen in der Leistungselektronik," Dissertation, Universität Stuttgart, Shaker Verlag, Düren 2023

N. Tröster, D. Beilharz and J. Roth-Stielow, "A novel algorithm for position estimation in coreless current measurement applications," 2016 18th European Conference on Power Electronics and Applications (EPE'16 ECCE Europe), Karlsruhe, Germany, 2016, pp. 1-9, doi: 10.1109/EPE.2016.7695598 

N. Tröster, B. Dominković, J. Wölfle, M. Fischer and J. Roth-Stielow, "Wide bandwidth current probe for power electronics using tunneling magnetoresistance sensors," 2017 IEEE 12th International Conference on Power Electronics and Drive Systems (PEDS), Honolulu, HI, USA, 2017, pp. 35-40, doi: 10.1109/PEDS.2017.8289128

N. Tröster, D. Bura, J. Woelfle, M. Stempfle and J. Roth-Stielow, "Design of a 300 Amps Pulsed Current Source with Slopes up to 27 Amps per Nanosecond for Current Probe Analysis," PCIM Europe 2017; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, Nuremberg, Germany, 2017, pp. 1-6.

N. Tröster, J. Wölfle, J. Ruthardt and J. Roth-Stielow, "High bandwidth current sensor with a low insertion inductance based on the HOKA principle," 2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe), Warsaw, Poland, 2017, pp. P.1-P.9, doi: 10.23919/EPE17ECCEEurope.2017.8099003

N. Tröster, J. Ruthardt, M. Nitzsche and J. Roth-Stielow, "Wide Bandwidth Current Sensor Combining a Coreless Current Transformer and TMR Sensors," PCIM Europe 2018; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, Nuremberg, Germany, 2018, pp. 1-7.

N. Tröster, T. Eisenhardt, M. Zehelein, J. Wölfle, J. Ruthardt and J. Roth-Stielow, "Improvements of a Coaxial Current Sensor with a Wide Bandwidth Based on the HOKA Principle," 2018 20th European Conference on Power Electronics and Applications (EPE'18 ECCE Europe), Riga, Latvia, 2018, pp. P.1-P.9.

P. Ziegler, N. Tröster, D. Schmidt, J. Ruthardt, M. Fischer and J. Roth-Stielow, "Wide Bandwidth Current Sensor for Commutation Current Measurement in Fast Switching Power Electronics,"" 2020 22nd European Conference on Power Electronics and Applications (EPE'20 ECCE Europe), Lyon, France, 2020, pp. P.1-P.9, doi: 10.23919/EPE20ECCEEurope43536.2020.9215686"