Wide-bandgap semiconductors have made and are continuing to make a major impact on the power electronics world. The most common commercially available wide-bandgap semiconductors for power electronics applications are SiC and GaN devices. This paper focuses on the newest devices emerging that are made with these wide-bandgap materials. The static and dynamic characterization of six different SiC MOSFETs from different manufacturers are presented. The static characterization consists of the output characteristics, transfer characteristics and device capacitances. High temperature (up to 150 °C) static characterization provides an insight into the dependence of threshold voltage and on-state resistance on temperature. The dynamic characterizations of the devices are conducted by performing the double-pulse test. The switching characteristics are also tested at high temperature, with the presented results putting an emphasis on one of the devices. A comparison of the key characterization results summarizes the performance of the different devices. The characterization of one of the SiC MOSFETs is then continued with a short-circuit failure mode operation test. The device is subjected to non-destructive and destructive pulses to see how the device behaves. The non-destructive tests include a look at the performance under different external gate resistances and drain-source voltages. It is found that as the external gate resistance is increased, the waveforms get noisier. Also, as the drain-source voltage is increased, the maximum short-circuit current level rises. The destructive tests find the amount of time that the device is able to withstand short-circuit operation. At room temperature the device is able to withstand 4.5 μs whereas at 100 °C, the device is able to withstand 4.2 μs. It is found that despite the different conditions that the device is tested at for destructive tests, the energy that they can withstand is similar. This paper also presents the static and dynamic characterization of a 600 V, 2A, normallyoff, vertical gallium-nitride (GaN) transistor. A description of the fabrication process and the setup used to test the device are presented. The fabricated vertical GaN transistor has a threshold voltage of 3.3 V, a breakdown voltage of 600 V, an on-resistance of 880 mΩ, switching speeds up to 97 V/ns, and turn-on and turn-off switching losses of 8.12 µJ and 3.04 µJ, respectively, demonstrating the great potential of this device / MS / A key part in a power electronics circuit is the switch component. Currently, the devices usually used as the switch are made from silicon. As the performance limits of silicon are reached though, wide-bandgap semiconductors are proving to be a promising alternative to silicon semiconductors. These wide-bandgap switches will allow for higher powers, higher efficiency and higher temperature operation. The technology is still novel though and so new devices are still being developed. This paper focuses on showing the performance of the newest devices emerging that are made with these wide-bandgap materials. To demonstrate the performance potential of a switching device, the non-switching and switching behavior need to be tested. These tests are described and the results are shown for both Silicon Carbide (SiC) and Gallium Nitride (GaN) semiconductors which are the most common wide bandgap semiconductors. The failure mode operation of one of the SiC devices is also tested. A common failure in power electronics is a short circuit failure where the switch is turned on for a long amount of time and kept on for too long, eventually leading to the device breaking destructively. To understand the limits and capabilities of these devices in a short circuit failure, non-destructive and destructive tests are explained and demonstrated.

With a higher power rating and broader application, Gallium nitride (GaN) is a promising next-generation power switch. The current four GaN HEMTs in paralleled phase leg that can block 400 V and conduct 200 A current is very beneficial, thus making the protection method on a GaN phase leg an urgent topic. This thesis starts with an overview of shortcircuit robustness among silicon (Si), silicon carbide (SiC) and GaN devices. An approximately safe operation area (SOA) for a GaN power switch will also be determined. The various common shortcircuit protection methods are mentioned. Additionally, current research on a GaN semiconductor is summarized. Among all of the protection methods, desaturation detection is selected and analyzed through simulation and then implemented in a parallel enhancement-mode high-electron-mobility transistor (E-HEMT) GaN phase leg. With this desaturation detection feature, the GaN E-HEMT can be turned off as quickly as 200 ns, and in the worst case, 500 ns, during a shortcircuit test. The phase leg survived a series of shortcircuit tests with shortcircuit protection. For the proposed protection scheme, the best-case reaction time (200 ns) is similar to others in the literature, while the shortcircuit peak current and peak energy are higher. The worst-case performance of this design is limited by both the gate driver and the device shortcircuit robustness. Due to the fast switching speed of the GaN HEMT, the false turn-on phenomenon caused by the Miller effect can be a problem. A shoot through may occur with one switch false turn on. The Miller clamp is added to the phase leg to improve its reliability. After the hardware was implemented, the Miller clamp was tested and verified through a double pulse test (DPT). Compared to the phase leg without the Miller clamp, the gate is better protected from gate voltage overshoot and undershoot. The switching loss is reduced by 20 percent by using a new gate driver IC with higher current driving capability. The degradation effect of GaN power switches in different shortcircuit pulses was also studied. The device passes through the shortcircuit tests, but any degradation effect that may change its parameters and influence its normal operation characteristic need to be addressed. Several GaN devices were selected and characterized after several shortcircuit tests to observe any degradation effect caused by the shortcircuit. The degradation test results reveal a "recovery effect" of the GaN HEMT used in this project. The parameter variations on threshold voltage and on-resistance recover to the original state, several hours after the shortcircuit test. The test results match with the conclusion drawn in degradation test conducts by other research groups that the parameter variation during shortcircuit test is negligible. Also, repetitively fast shortcircuit tests on the GaN HEMT show that the shortcircuit protection limit for this device under 400 V bus should be limited to 300 ns. / Master of Science / A phase leg consists of two power switches: a top switch and a bottom switch. As a result of a wrong gate signal or the Miller effect, shoot through problems may occur that lead to a shortcircuit current running through the channel. The excessive heat brought by the shortcircuit current will kill the device if not turned off in time. The failure of the phase leg may also have a hazardous impact on the rest of the system. To improve the overall system stability, a shortcircuit protection feature can be added on the gate-drive level. The shortcircuit protection turns off the device when it runs into shortcircuit mode, and before device failure. In this thesis, desaturation detection is selected to implement on a paralleled Gallium nitride (GaN) phase leg based on the device characteristic and configuration. Desaturation detection takes the device under test (DUT) as a current sensing component. By sensing the voltage across the DUT, the desaturation detection decides whether the DUT is operating under shortcircuit. If it is, a signal is sent to the gate driver to turn off the DUT when high voltage is sensed. A series of shortcircuit tests were conducted to verify the function of shortcircuit protection. A Miller clamp is also implemented and tested on the same phase leg to prevent a false turn on problem and to protect the gate. Both the Miller clamp and desaturation v detection features are tested on the same phase leg. The GaN devices survive the shortcircuit tests, with shortcircuit protection times between 200 ns to 500 ns. The design is successfully validated. Along with the implemented protection features, device degradation and shortcircuit robustness tests are also included in this work. The test results show that 300 ns shortcircuit time under 400 V bus is a safe turn off goal for this device.

Master’s thesis deals with computation of steady state and short-circuit conditions in the 110 kV distribution network in the nodal area of Čebín. Computations are done during independent operation and bridge operation of transformers T401, T402 in transformation station Čebín with proposed configuration of network. Additional computations of steady state during specific operating conditions such as (T401 outage, disconnection of line 5553) were done during network operation in bridge operation of T401, T402. Voltage conditions in substations, load of 110kV lines and 400/110 kV, 110/HV kV transformers are evaluated based on the computations of steady state. Short-circuit resistance of substations is being evaluated with the aid of calculations of short-circuit conditions. There is a comparison and processed results of computations during independent operation, bridge operation, special operational states and proposed technical measures of operation in bridge operation in the end of the thesis. Theoretical part of the master’s thesis deals with the description of 110 kV distribution networks, theory of calculation of the steady state of electric system with the aid of Newton iterative method a calculation of single-phase and three-phase short-circuit current with the aid of method of symmetrical components.