Subhadra Tiwari

SiC MOSFETs for future motor drive applications

This paper investigates the switching performance of six-pack SiC MOSFET and Si IGBT modules for motor drive applications. Both the modules have same packaging and voltage rating (1.2 kV). The three bridge legs of the modules are paralleled forming a single half-bridge configuration for achieving higher output power. Turn-on and turn-off switching energy losses are measured using a standard double pulse methodology. The conduction losses from the datasheet and the switching energy losses obtained from the laboratory measurements are used as a look up table input when simulating the detailed inverter losses in a three-phase motor drive inverter. The total inverter loss is plotted for different switching frequencies in order to illustrate the performance improvement that SiC MOSFETs can bring over Si IGBTs for a motor drive inverter from the efficiency point of view. The overall analysis gives an insight into how SiC MOSFET outperforms Si IGBT over all switching frequency ranges with the advantages becoming more pronounced at higher frequencies and temperatures.

Design considerations and laboratory testing of power circuits for parallel operation of silicon carbide MOSFETs

In this paper, the impact of using parallel SiC MOSFETs as the switching device is investigated. Measurement considerations for a double pulse test are discussed, and the influence of the load inductor characteristic and the voltage measurement technique on the measurement results is demonstrated. It is shown that the inductor load can produce high frequency oscillations of up to 10 % of the load current in the switching current, which can wrongly be associated with the switching device. It is also shown that the standard earth connection of passive voltage probes can induce an extra stray inductance in the measurement loop, which can lead to a measurement of an extra overvoltage of up to 50 V, which is not due to the actual switching. Moreover, the dependency of turn-on and turn-off losses on the load current and the dc-link voltage is presented. It is shown that doubling the load current would increase the switching losses more than the double amount. Therefore, use of two parallel MOSFETs instead of a single one would decrease the total switching losses for a given load current. On the other hand, the parallel configuration is shown to have a higher overvoltage than one single MOSFET for a similar load current. This, however, can be reduced by a higher gate resistance which will eventually keep the total switching loss of parallel configuration equal to the single MOSFET configuration for a given load current. Finally, it is also shown that switching losses can be greatly decreased by decreasing the gate resistance, but this leads to a higher overvoltage on the device. Therefore, the final choice for design is a compromise between the switching losses and the overvoltage.

Design of low inductive busbar for fast switching SiC modules verified by 3D FEM calculations and laboratory measurements

This paper explains the importance of low inductive busbar for utilizing the fast switching feature of SiC modules. A 3D FEM model of the busbar is built using Ansys Q3D extractor. The simulation results give insight into the physical behaviour of the current flow which aids in the identification of the parts of the structure that must be considered coplanar. The simulated busbar inductance is compared with analytical values and laboratory measurements, and possible reasons for deviations are discussed. Based on this knowledge, different alternative low inductive busbar designs are presented through FEM simulations along with the laboratory measurements for one of the simulated solutions, which are the main contributions of the paper.

Experimental evaluation of switching characteristics, switching losses and snubber design for a full SiC half-bridge power module

This paper analyzes the switching performance of the full SiC half-bridge power module BSM120D12P2C005 from Rohm Semiconductor. It investigates if the combination of a DC snubber and a turn-off snubber helps to reduce sufficiently the electrical stresses on hard-switching power modules. Simulations in LTspice IV and laboratory experiments give the basis for the analysis. Standard double-pulse tests of the module are conducted at different drain currents. This makes it possible to analyze the switching characteristics and the total switching losses of the SiC module. Simulations in LTspice are used in order to investigate if the use of suitable snubber circuits improves the switching transients. The performance of these snubbers is tested and verified through laboratory experiments. It is shown in both simulations and laboratory experiments that a simple and well-known DC snubber circuit for half-bridge configurations attenuates ringing without reducing the voltage overshoot. In order to suppress this extensive voltage overshoot to an acceptable level during device turn off, a turn-off snubber must be added to the circuit. It is found that this solution does not increase the switching losses significantly.

Experimental performance evaluation of two commercially available, 1.2 kV half-bridge SiC MOSFET modules

In this paper, the switching performances of two state-of-the-art half-bridge SiC MOSFET modules are evaluated using a standard double pulse test methodology. The selected modules are commercially available, and have the same voltage and current ratings. A comparative study is carried out under various conditions such as similar dv/dt, di/dt, and current and voltage overshoots. Additionally, the lab setup is simulated in LTspice in order to investigate the impact of stray inductances in the switching performances. Both the simulations and the experimental measurements give insight in the significance of low inductive layouts to utilize the fast switching feature of SiC.

Comparative evaluation of a commercially available 1.2 kV SiC MOSFET module and a 1.2 kV Si IGBT module

In this paper, a comparative performance evaluation of a 1.2 kV SiC MOSFET module and a 1.2 kV Si IGBT module is carried out under a series of different conditions such as similar dv/dt, di/dt, voltage overshoot, current overshoot, and ringings. Both the modules are commercially available in a standard plastic package and have the same stray inductances. Various parameters such as switching speed, energy loss, and overshoots are experimentally measured in order to address the comparative advantages and disadvantages of the selected modules. This paper demonstrates that SiC MOSFET can replace Si IGBT of similar voltage class or even higher voltage class, both in slow and fast switching applications.