David Hirning, M.Sc.

Zusammenfassung

Hybrid current sensors are suitable for wide bandwidth current measurement. They entail the fusion of two different measurement circuits, one for DC and low-frequency current and another for high-frequency current. Thus, the advantages of the different measurement principles are incorporated in one current sensor. Hybrid current sensors generate output signals through a superposition of the signals from the low-frequency and high-frequency current sensors. This is realized using analog signal processing by means of an analog operational amplifier circuit. Realization of the superposition of the frequency responses of the different measurement circuits to achieve a constant gain in the transition area is challenging. This study focused on the analog signal processing and its enhancement. Specifically, two possible signal processing approaches to increase the bandwidth based on the state-of-the-art realization of a low-pass filter were devised. These approaches were investigated using a simulation model. Frequency response measurements using a hybrid current sensor based on tunneling magnetoresistance sensors and a Rogowski coil were used for verification. The results show that by enhancing the signal processing, the bandwidth of the current sensors can be significantly increased.

Zusammenfassung

Hybrid current sensors are suitable devices for wide bandwidth current measurement. They combine two different measurement circuits, one for DC and low-frequency current measurement and another for high frequency current measurement. This combines the advantages of different measurement principles in one current sensor. The output signal of the hybrid current sensor is generated through a superposition of the low-frequency and high-frequency current sensor. This is realized using analog signal processing by means of an analog operational amplifier circuit. The challenge is to superpose the frequency responses of the different measurement circuits achieving a constant gain in the transition area. This paper focuses on the analog signal processing and its optimization. Based on a state-of-the-art realization, two possible optimization approaches of the signal processing are presented to increase the bandwidth. These optimization approaches are investigated in a simulation model and verified by frequency response measurements of a hybrid current sensor based on tunneling magnetoresistance sensors and a Rogowski coil.

Zusammenfassung

This paper presents a method for junction temperature monitoring of SiC-MOSFETs based on a high-frequency gate-signal injection. The signal is injected during steady state (e.g. off-state) resulting in a current response, which depends on the temperature dependent gate impedance. The external gate resistor is used as a current shunt to capture the current response. The resulting signal contains the junction temperature information due to the temperature dependency of the gate impedance. This paper focuses on a sinusoidal approach to overcome the challenges due to the temperature dependent parasitic capacitance of the gate circuit. Measurements show the proof of concept, however, there are still challenges to face.

Zusammenfassung

Conventional filters needed for the electromagnetic compatibility lower the system power density by consuming additional space in power electronic setups. To increase the power density, alternatives for these filters are needed. If the power electronic setup offers the possibility to synchronize two opposing switching transitions, the common mode noise can be reduced without additional filters. In this case two opposing noise currents reduce one another by superimposition. For power electronic setups which do not offer the possibility to synchronize switching transitions, this paper presents an approach which uses additional half bridges as opposing noise sources connected to a replicated grounding impedance to create the opposing common mode noise. The main goal of the opposing noise source is to create similar potential changes as the power electronic setup over the replicated grounding impedance. The replicated grounding impedance emulates the grounding impedance of an ohmic inductive load with discrete elements. The achieved reduction of the common mode noise with this approach is evaluated with measurements.

Zusammenfassung

This paper focuses on the capacitive coupling of PCB integrated Rogowski coils for commutation current measurement. It investigates the cause and the influence of parasitic capacitances on the measurement signal. It discusses the advantages of a differential winding arrangement and the reasons why shielding is not an option in this application. The parasitic capacitance of three different winding arrangements are measured and compared to a Rogowski coil approach with minimized parasitic capacitance. On the base of sensor prototypes, the influence on the measurement is investigated in a pulsed current source.

Zusammenfassung

For the optimal design of power electronic systems the exact knowledge about the different loss mechanisms of the used semiconductor devices is essential. However, conventional measurement methods based on electrical parameters are facing their limits, as switching speed of modern power devices is steadily increasing enabled by the use of wide bandgap semiconductor materials. For this reason, calorimetric measurement techniques are becoming more and more popular. However, due to the nature of their principle, calorimetric measurement methodologies can usually only determine the total power losses of the device under test. To overcome this disadvantage a methology which combines different calorimetric and electrical measurements to separately determine the switching and conduction energies in a half-bridge with an ohmic-inductive load while maintaining the accuracy of calorimetric measurement methods is developed. In addition, the presented methodology identifies the switching energies of the two different switching transitions within one switching period, depending on the load current as well as the dead time, considering thermal influences. A hardware setup for the presented methology, is realized. Using this test setup, the loss energies of a half-bridge based on silicon carbide MOSFETs are investigated. The resulting measurements are presented and verified by measurements with a power analyzer.

Zusammenfassung

This paper presents investigations on the suitability of using the gate-signal injection method for junction temperature measurement of SiC-MOSFETs. The method is based on the temperature sensitivity of the internal gate resistance. A high frequency signal is injected into the gate circuit while the MOSFET is operating. The response of the injected signal is a high frequency current, which depends on the temperature sensitive gate circuit’s impedance. This current causes a voltage drop across the external gate resistor. This voltage depends on the junction temperature and is evaluated. This method was successfully implemented on Si-IGBTs in the past. However, there are challenges to face in implementing this method on SiC-MOSFETs. This paper shows the challenges and proposes solutions to overcome them.