This study compares SiC two-level converters with hybrid Si/SiC and full-SiC three-level converter topologies for low-voltage and low-power applications in terms of electrical performance. Analytical loss models are derived for each topology and the loss models are iteratively solved with a thermal equivalent circuit. The results show that full-SiC three-level converters are slightly superior to hybrid Si/SiC equivalents in terms of output power capability and converter efficiency. Moreover, three-level converters do not offer major electrical performance improvements compared to two-level converters if SiC is used. The switching frequencies at which three-level converters are better than two-level converters are shifted to relatively high frequencies for SiC-MOSFETs compared to Si-IGBTs. For 400 V AC systems, two-level SiC converters are the most attractive option. For 690 V AC systems, three-level topologies can not be dismissed because 2300 V SiC chips are not available in the market yet.

Digitally controlled switch-mode power conversion systems require an embedded computing platform to execute, in real-time (RT), closed-loop algorithms that regulate the power flow. Since legacy control software design is traditionally rooted to single-core processors, recent trends in power electronics toward faster switching devices and multilevel topologies will challenge their computational capacity and reliability to meet RT deadlines. With Internet-of-Things driving down the cost of a general-purpose system-on-chip (SoC), combining a multicore application processor and a field-gate programmable array (FPGA) on single device, this article introduces a codesign workflow and a runtime architecture for the heterogeneous deployment of multirate control algorithms. Code migration toward the FPGA exploits high-level synthesis, while a Linux-Xenomai dual-kernel operating system manages the synchronization and the parallel execution of the tasks. Following sections will describe and benchmark the selected key technologies and validate them on a small-scale grid-connected converter emulator.

This paper reports wide reverse bias safe operating area (RBSOA) and surge current capability in 6.5kV/8A SiC MOSFET power devices. The results indicate robustness of 6.5kV devices tested at $125^{\circ}\mathrm{C}$ under turn-off SOA conditions at V$_{D} =$ 5000V up to four times nominal current density (4x $\mathrm{J}_{\mathrm{NOM}}=160 \mathrm{Acm}^{-2}$). The surge current capability of the MOS-channel has been tested up to 10x JNOM, and for pulse duration up to 10ms. The observed voltage waveforms, after applying two current pulses at 320Acm$^{-2}$, show high reproducibility. Minor variations between the two voltage pulses were observed for current values above 400Acm$^{-2}$. Remarkably, the MOSFET devices do not get destroyed while tested at this higher limit.

The combination of the robust low-loss RC-IGCT technology with the modular multi-level converter (MMC) technology is a key enabler for high-power MV applications from 50 to 500 MV A. The RCIGCT technology covers cost-efficiently phase currents in the range from 1000Arms up to 3500 Arms. Future bi-mode BGCT technologies will enable even higher currents without any parallel connection up to 5000 Arms. The ceramic presspack housing of the RCIGCT in combination with the IGCT clamp network allows a unique and safe plasma containment in all fault cases. Future high power MV application like pumped hydropower, MVDC collection grids for renewables, interties for distribution grids and future MVDC distribution backbones can be served at leading costs and efficiency levels. The low-loss RCIGCT technology is inherently a future option at higher voltage levels, i.e. in HVDC applications.

Medium Voltage DC (MVDC) is a key word which covers a wide area of applications, from well-known 3 kV DC railway network via DC distribution networks within vehicles/vessels or cities, via DC collection grids to even MVDC transmission. From the perspective of a supplier of solutions based on power electronic converters, the paper gives a survey of MVDC applications, technical solutions, required key components, the state-of-the-art solutions and those expected to be available soon. Further, considerations on the advantages and disadvantages of using MVDC in the mentioned applications are included.

A large area (150mm) high voltage (6.5kV) Reverse Conducting-Integrated Gate Commutated Thyristor (RC-IGCT) has been developed for low frequency high power electronics applications. The devices were fabricated with GCT to diode active area ratio of 1.4. The RC-IGCT wafers were designed with an outer ring gate structure to minimize the stray impedance for the gate signal and also to improve the thermal behavior of the device. In addition, the HPT+ (High Power Technology) platform has been employed in the GCT part to increase the safe operation area of the device (to achieve high controllable turn-off current capability). In this paper we present the measurement results of the 150mm, 6.5kV RC-IGCT during conduction and turn-off in both GCT (switch)- and diode-modes of operation. In addition, we have compared the technology trade-off curve of the 150mm, 6.5kV RC-IGCT with the state-of-the-art 6.5kV HiPak IGBT modules in switch-mode.

Pumped hydropower is gaining importance as a key technology for the integration of large quantities of renewable electricity, in particular from wind and solar sources. With the progress in power electronics, it has recently become possible to build frequency converters with a rated power in excess of 100 MVA, paving the way for a new variable speed pumped hydropower solution based on synchronous machines whose stator is driven with a variable frequency. This solution, refered to as converter fed synchronous machine (CFSM), is offering even higher flexibility and efficiency than DFIM (doubly-fed induction machine). A first CFSM plant with a rated power of 100 MVA has been installed in Switzerland and has been in productive operation since late spring 2013. As a further step a new CFSM power converter type based on modular multi-level converter (MMC) technology is proposed. This topology, powered by advanced IGCT (integrated gate-commutated thyristor) power semiconductor devices, enables a total power conversion efficiency greater than 98.5%. Very smooth waveforms and special starting algorithms make it possible to use standard generator and transformer insulation schemes. Due to a modular converter construction, the accessible range of rated power spans from approximately 50 MVA up to 500 MVA. Built-in redundancy enables a very high availability.

Modular multilevel converters (MMCs) require isolated power supplies at their cells (modules). For high voltage MMC cells with considerable power consumption, simple flyback converters are no more applicable as power supplies; however, input-series output-parallel (ISOP) flyback converters are suitable provided that simplicity and cost-effectiveness are preserved. In this paper, a simple 100W 2.8kV-to-36V 3-stage ISOP flyback converter is proposed as high voltage cell power supply (HV-CPS). In this paper, the HV-CPS's implementation challenges are addressed and their solutions are provided. Via the full-scale prototype of the proposed HV-CPS, its successful operation is experimentally demonstrated.

In this paper, protection of modular multilevel converter with half-bridge cells against overcurrent faults, which cannot be cleared by the converter, is investigated. Converter design with cell redundancy and a coupled branch reactor is considered. Special consideration is given to a separation of protection and permanent bypass functionality. Critical overcurrent protection design aspects are shown and supported by experimental data. Impact of reactor inductance mismatch in the branches on overcurrent protection design is investigated. This work was carried out within the frame of European FP7 program and its support is gratefully acknowledged.

In this paper, the reliability of medium voltage multilevel converters based on cascaded cells is investigated. Limits of reliability prediction and redundancy application are shown. Opportunities to leverage converter predicted reliability with redundancy are analyzed. Special attention is given to the impact of the bypass device on converter reliability.The analysis shows significant influence of redundancy on power stage failure rate reduction. At a certain redundancy level though, control hardware will play a dominant limiting role in converter reliability. The analysis also shows the existence of maximum power stage redundancy level for a given bypass failure rate. Exceeding this level results in reduction of converter reliability.This work was carried out within the frame of European FP7 program and its support is gratefully acknowledged.

Airborne Wind Turbines (AWT) represent a radically new and fascinating concept for future harnessing of wind power. This concept consists of realizing only the blades of a conventional wind turbine (CWT) in the form of a power kite flying at high speed perpendicular to the wind. On the kite are mounted a turbine, an electrical generator and a power electronics converter. The electric power generated is transmitted via a medium voltage cable to the ground. Because of the high flight speed of the power kite, several times the actual wind speed, only a very small swept area of the turbine is required according to Betz's Law and/or a turbine of low weight for the generation of a given electric power. Moreover, because of the high turbine rotational speed, no gear transmission is necessary and the size of the generator is also reduced. For takeoff and landing of the power kite, the turbines act as propellers and the generators as motors, i.e. electric power is supplied so that the system can be maneuvered like a helicopter. In the present work the configuration of power electronics converters for the implementation of a 100kW AWT is considered. The major aspect here is the trade-off between power-to-weight ratio (W/kg) and efficiency. The dependence of cable weight and cable losses on the voltage level of power transmission is investigated, and a comparison made of low voltage (LV) and medium voltage (MV) versions of generators. Furthermore, the interdependence of the weight and efficiency of a bidirectional Dual Active Bridge dc-dc converter for coupling the rectified output voltage of a LV generator to the MV cable is discussed. Based on this, the concept offering the best possible compromise of weight and efficiency in the power electronics system is selected and a model of the control behavior is derived for both power flow directions. A control structure is then proposed and dimensioned. Furthermore, questions of electromagnetic compatibility and electrical safety are treated. In conclusion, the essential results of the work are summarized and an outlook on future research is given. To enable the reader to make simplified calculations and a comparison of a CWT with an AWT, the aerodynamic fundamentals of both systems are summarized in highly simplified form in an Appendix, and numerical values are given for the 100kW system discussed in this work.

This paper introduces a novel hybrid seven-level converter that is based on the upgrade of the five-level active neutral-point-clamped converter concept and is suitable for high-power applications. The paper provides a comprehensive analysis for the operation of the converter. Based on the analysis, a space vector modulation (SVM)-based switching strategy that takes advantage of redundant switching vectors of the SVM strategy to counteract the voltage drift phenomenon of the proposed converter is proposed. The limit to the range of operation of the seven-level converter based on the proposed SVM strategy is also presented. It is shown that the ability to stabilize the dc-link capacitor voltages and the per-phase flying capacitors is a function of the converter operating indices, i.e., the load power factor and modulation index. The salient feature of the proposed SVM-based control strategy is that it enables proper operation of the converter with no requirements for additional controls or auxiliary power circuitry, within the specified range of operation. Performance of a converter under various operating conditions, based on the proposed SVM strategy, in the MATLAB/Simulink environment, is evaluated and experimentally demonstrated.