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The three-level neutral-point-clamped voltage-source converter (NPC VSC) is widely used in high-power medium-voltage (MV) applications. To overcome its major drawback--the unequal loss distribution among the semiconductors-the use of active NPC (ANPC) switches was previously proposed. In this paper, a simple feedforward loss-control scheme for the ANPC converter is presented. The principle of operation of the ANPC VSC is experimentally verified for the first time. Electrical measurements on a low-voltage test bench prove the proper function of the ANPC converter. Infrared junction temperature measurements confirm the improved loss distribution using the new loss-control scheme. Finally, the authors demonstrate the superior performance of the loss-controlled ANPC converter in various MV applications. Index Terms--Medium-voltage (MV) converters, multilevel converters.

This paper describes the design of a (4-kV, 4.16-MVA) three-level neutral-point-clamped-, three-level flying-capacitor-, four-level flying-capacitor-, and nine-level series-connected H-bridge voltage-source converter on the basis of state-of-the-art 6.5-, 4.5-, 3.3- and 1.7-kV insulated gate bipolar transistors. The semiconductor loss distribution and the design of semiconductors and passive components are compared for a medium switching frequency assuming a constant converter efficiency of about 99%. To evaluate the converter characteristics in high switching frequency applications, a second comparison is realized for the maximum switching frequencies assuming a constant expense of semiconductors in all converters. Index Terms--Medium-voltage drives (MVDs), multilevel converters, power electronics.

This paper evaluates three-level topologies as alternatives to two-level topologies in converters for low-voltage applications. Topologies, semiconductor losses, filter aspects, part count, initial cost, and life-cycle cost are compared for a grid interface, a conventional drive application, and a high-speed drive application. Index Terms--Life-cycle cost, multilevel converters, semiconductor losses.

High-frequency simulation models for power cables and motors are key tools to aid a better understanding of the overvoltage problem in pulsewidth modulation drives with long feeders. In this paper, frequency responses of the cable characteristic and the motor input impedances are obtained experimentally and suitable models are developed to match the experimental results. Several lumped segments incorporating a lossy representation of the line are used to model the cable. The cable and induction motor models may be implemented using a computational tool such as MATLAB, thereby providing a convenient method to analyze the overvoltage phenomena. Simulation and experimental results are presented for a typical 3-bp induction motor, showing the suitability of the developed simulation models. The most promising dv/dt filter networks are also investigated through simulation analysis, and a design approach based on a tradeoff between filter losses and motor peak voltage is proposed. Experimental results of an RC filter placed at the motor terminals demonstrate the validity of the simulation models. Index Terms--Adjustable-speed drives, converter machine interactions.

This paper compares hard-driven gate-turn-off thyristors (IGCT's) and high-power insulated gate bipolar transistor (IGBT) modules in a two-level pulsewidth modulation inverter. The structure, fundamental operation, and specific characteristics of the considered devices are shown. Simulations enable a loss comparison of IGCT's and IGBT's in a 1.14-MVA inverter at switching frequencies of [f.sub.s] = 2.50 Hz/500 Hz. The evaluation of device characteristics is the basis for a derivation of potential applications. Index Terms - Hard-driven gate-turn-off thyristor, insulated gate bipolar transistor, losses, pulsewidth modulation inverter.

This paper investigates the feasibility of a quasi-resonant dc-link soft-switching principle for voltage-source inverters (VSIs) in the megawatt power range. An evaluation of a three-level quasi-resonant dc-link VSI (3L-QRDCLVSI) featuring integrated gate-commutated thyristors (IGCTs) and a comparison to a commercially available three-level IGCT-VSI is presented. Extensive loss measurements of IGCTs under hard- and soft-switching conditions are the basis for the design and the comparison of the inverters. Aside from converter losses, other important aspects such as control, protection, and reliability are addressed. Index Terms--Integrated gate-commutated thyristor, pulsewidth modulation converter, soft switching, three-level converter.

In order to fulfill the grid codes and meet power quality requirements in grid-connected converters without increasing the switching frequency or system size, higher order line filters are often used. This paper considers the active damping of $LC\!L$-filters in grid-connected converters. Analysis in the discrete time domain shows that the damping can be increased when proportional plus derivative control of the capacitor current is applied, and it is found that this scheme has a simple implementation in a discrete time system as it is equivalent to proportional feedback of the last two samples. To find optimal damping controller gains, an analytical solution is derived for the open-loop system, and for the closed-loop system, a numerical optimization algorithm is developed. The performance of the proposed methods is compared using analysis in the $z$-domain, simulations, and experimental investigation. The analytical solution has good damping, an easy implementation, and is seen to have robustness against parameter variation, whereas the numerical solution is computation intensive but has even higher damping. [ABSTRACT FROM AUTHOR]