IGCT Based Solid State Resonant Conversion

Driven by the environmental changes, penetration of renewables and the need for more flexible power grid, DC is reemerging as a basis for future power networks. Already established in the area of HVDC for very long distance transmission, more and more attention is drawn to DC for distribution purposes, especially MVDC collection grids for offshore wind farms, solar parks, ship distribution. To realize such a system, safe, reliable and efficient interconnection of different voltage levels within the power network has to be achieved. Considering that the traditional AC transformer cannot be used for this function, power electronics based DC-DC converters must take over, opening a wide area of research focused around the idea of the DC transformer. Given the state of the art of DC-DC topologies, LLC-SRC was chosen for testing the viability of application of the IGCT to meet the high efficiency and reliability demands. The potential of these heavy duty devices was highly overlooked due to the popularity of the IGBT. Sub-resonant operation of the LLC-SRC was analyzed and advantages of operation are outlined. Zero voltage turn-on, low current turn-off and the clamp-less operation with IGCT is theorized promising the high efficiency of the final converter. Simplified design guidelines are summarized as a result of the theoretical analysis providing a quick tool for the future designer to use. Based on these guidelines, a physical test setup was built for multifunctional purposes, capable of testing single and series connected IGCTs under hard-switching and resonant operating conditions. Furthermore, it was designed to operate in the continuous steady state simulating the LLC-SRC operation of the IGCT half-bridge. As the low current hard-switching data is not always available in the datasheet of the IGCT, these tests were performed first. TCAD simulation was initially used to gain understanding into the turn-off behavior followed by the experiment on the test setup. Single- and double-pulse tests were performed and data was summarized for both turn-on and turn-off process. The results served as a baseline for comparison with the resonant based tests and determine if the switching behavior is different for the two switching operation types. The developed tests provided invaluable insight into the switching operation of the IGCT under resonant conditions. Single resonant pulse test was used to observe the turn-off behavior including transient duration, switching losses estimation and over-voltage. The initial results were used to clearly define the required dead-time for the next set of pulse testing - double resonant pulse testing. This test proved the viability of the IGCT operation under the zero-voltage turn-on and switching without the clamp circuit. Finally, the continuous operation of the test setup was demonstrated with IGCTs switching in resonant operation mode. Relatively high switching frequency was achieved for this type of MV voltage switches, mostly used in hard-switching applications with switching frequencies of up to 900Hz. Exclusion of the clamp circuit was justified and practically proved without any damage to the IGCTs under test. Proper selection of the dead-time in the switching bridge ensured zero voltage turn-on of the switching devices with further decrease in switching losses achieved by low current turn-off. High conversion efficiency of the half-bridge was reached for the nominal operating conditions defined by