This paper presents a strategy for protecting high power IGCT-based converters which are currently used in a wide range of drive applications. The protection of such converters against internal faults has been addressed in the technical literature, but the main focus has been on the solutions to disconnect the converter from the mains. In this paper, the short circuit current paths through the power devices are identified and studied from the perspective of keeping the overall repair cost after a fault to a minimum. It is shown that a preferred short-circuit current path that limits the thermal energy in all IGCTs to safe levels exists. Furthermore, it is demonstrated that it is possible to guarantee, through proper busbar geometry and/or device selection, that the short-circuit current stress can always be moved to the power diodes. Simulation results are presented to support all the discussions and conclusions, avoiding the costs and risks of tests on a medium voltage prototype. 1
This work present the development of an electronically controlled harmonic mitigation device with the property that it can inserts specific series harmonic impedances in the electric system. These harmonic impedances are inserted only at specific frequency (or frequencies). It can be utilized, for example, to active detune power factor capacitor banks, limiting the harmonic current through the capacitors without the need for capacitor voltage rating increase, as it does not significantly changes the fundamental voltage at the capacitors. Also the system can be used for implementation of shunt hybrid harmonic filters or be applied on distributed harmonic mitigation strategies, obtaining a flexible and cost-effective solution even for high power applications. Other advantage of the proposed system is the reduced converter rating necessary for the selective harmonic impedance implementation. The utilization of single turn secondary coaxial transformers, where the secondary side is composed only by the power system cable, for harmonic impedance coupling, gives a significant flexibility to its application, allowing an easy application on existing systems, minimizing the downtime for solution implementation and performance evaluation.
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