Search

Integrated gate-commutated thyristors (IGCTs) have successfully demonstrated to be well-suited devices for an application in medium-voltage dc transformers based on LLC resonant converter topology. This appli- cation enables unusually high switching frequencies in kilohertz range thanks to the zero-voltage switching while maintaining the high conversion efficiency. Moreover, the clamp circuit that is an inseparable part of every hard-switched IGCT-based converter can be completely omitted—further lowering the converter complexity and cost. Nevertheless, without the clamp circuit, the effect of shoot through becomes fatal, considering that the IGCTs have a defined mode of failure in short circuit and the desaturation effect is practically nonexistent. To prevent the shoot through, this letter proposes a simple, yet effective, protection method based on anode-voltage measurement that can be implemented locally on the IGCT gate unit. The validity of the solution is demonstrated using a custom IGCT gate unit in a medium-voltage resonant test setup. [ABSTRACT FROM AUTHOR]

Recently, integrated gate-commutated thyristors (IGCTs) have shown a great potential for the soft-switching dc transformer applications based on LLC resonant converter. The zero-voltage switching that is present in this converter topology enables an operation of IGCTs without clamping circuit and with significantly higher switching frequencies, while maintaining the exceptionally low conduction losses. The high voltage and current ratings of the IGCTs make them a preferred choice for an efficient bulk power transmission. This article shows how gate units for IGCTs can be optimized for this soft-switching application. It presents a simplification of the driving topology and the design process for high switching frequencies. This results in low power consumption and a very small size of the gate unit. The prototype of the gate unit is built and experimentally validated in a 2.5 kV 0.75 kA resonant operation of the IGCT. [ABSTRACT FROM AUTHOR]

In the last thirty years, the integrated gate-commutated thyristor (IGCT) has been employed in medium voltage $\,\mathrm{M}\mathrm{W}$ power level converters and has demonstrated some of the lowest conduction losses of any actively controlled device in traditional hard-switched, sub- $\,\mathrm{k}\mathrm{Hz}$ applications. Extending the use of the device to medium frequency applications, such as dc transformers is possible through soft-switched operation, where low turn-off current and zero-voltage turn-on significantly reduce switching losses. For this purpose, this article explores the tradeoffs in the transition between zero-voltage and zero-current switching conditions of reverse conducting IGCTs. Switching conditions resulting in minimal switching loss are identified for standard commercial devices and engineering samples subjected to increased electron irradiation to reduce switching energy at the expense of on-state voltage. The operation of the IGCTs at the record frequency of 5 $\mathrm{k}$ $\mathrm{Hz}$ is thermally validated under load in the identified switching conditions. [ABSTRACT FROM AUTHOR]

The duty-cycle control is a popular option for current limiting in LLC resonant converters. Such current limiting is required to protect the converter either during the start-up or during an overload. Although this method proved to be effective, the switching and conduction losses of the converter are increased because of the modified current waveforms in the resonant tank. Hence, for the safe operation, it is vital to distribute the losses between the switches symmetrically. However, the conventional duty-cycle or phase-shift modulation methods do not provide this naturally. This letter elaborates on a method that was proposed for a different soft-switching topology more than a decade ago to solve this problem, and is adaptable for the emerging dc transformers. Furthermore, a simple implementation of the method is shown and the equal distribution of losses is validated experimentally. The VHDL code with the implementation of the modulator is attached to this letter available openly for reuse. [ABSTRACT FROM AUTHOR]

This letter presents an approach for modular multilevel converters that enables a stable operation with failed nonredundant modules. This is achieved by using a neutral shift with a dedicated power feed-forward control. The feasibility of the approach is verified by simulation. [ABSTRACT FROM AUTHOR]

The modular multilevel converter is a well-known modular multilevel topology. This paper proposes a novel branch inductor coupling and compares it to the center-tapped inductor and the standard noncoupled inductor topology. The proposed coupling has a significant influence on the inductor and converter dimensioning. Its properties make it especially well suited for use in single-to-three-phase ac/ac modular multilevel convert-er applications. [ABSTRACT FROM PUBLISHER]

The modular multilevel converter offers benefits for medium and high voltage power conversion due to indirect series connection of devices. The drawback is a large amount of capacitance that has to be installed in each module, often prohibiting its use in cost sensitive applications. This letter proposes a new operation mode of modular multilevel topologies that allows reducing the capacitance by at least an order of magnitude. To achieve this, the multilevel operation is sacrificed, but many advantages of indirect series connection, such as proper voltage sharing, small voltage steps, limited voltage slopes, modularity, and scalability remain. [ABSTRACT FROM AUTHOR]