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This paper introduces a new iterative design procedure of L and LCL filters for low-voltage active-front-end PWM two-level voltage source converters. The analytical expression of the converter harmonic voltages by Bessel functions is applied to design the filter parameters for defined maximum grid current harmonics. Different filter designs are derived for various resonance frequencies and inductance split factors of LCL filter. The minimum amount of stored energy of passive components is used to select a final filter design. A voltage-oriented control scheme, including active damping, is applied in the (400 V and 50 kVA) experimental setup. Both simulation and experimental investigations are presented to verify the accuracy of the filter design procedure. Finally, the steady state and transient performance of the active front end with different LCL filters are depicted. Index Terms--Active damping, active front end, LCL filter.

The application of a particular medium-voltage converter in a certain application depends on numerous criteria. However, in completely new installations, the choice of the system voltage is very often uninhibited of external constraints. Then, the voltage level shall be selected to enable the most efficient power conversion at the lowest cost. This paper is dedicated to help in finding the best voltage level for three-level neutral-point-clamped voltage source converters (3L-NPC VSCs) with respect to the power semiconductor devices. Three insulated-gate-bipolar-transistor-based 3L-NPC VSCs of different voltage levels (2.3, 3.3, and 4.16 kV) are investigated and compared regarding their maximum output power, semiconductor efficiency, and semiconductor cost per MVA output power. The effects of thermal cycling, the loss distribution within the converter, and switching frequencies from 300 to 1050 Hz are considered in the evaluation. Index Terms--Insulated gate bipolar transistor (IGBT) converters, medium-voltage (MV) converters, three-level converters.

This paper, along with an earlier published paper as Part 1, provides a comprehensive review of the state of the art of high-power converters (above 1 MW) for adjustable-speed ac drives. In this highly active area, different converter topologies have been developed for various drive applications in the industry. Due to its extensive coverage, the subject is divided into two parts: multilevel voltage source and current source converter topologies. This paper is focused on the second part and covers the current source converter technologies, including pulsewidth-modulated current-source inverters (CSIs) and load-commutated inverters. In addition, this paper also addresses the present status of the direct converter, which is also known as cycloconverter (CCV). This paper focuses on the latest CSI and CCV technologies and an overview of the commonly used modulation schemes. It also provides the latest technological advances and future trends in CSI- and CCV-fed large drives. This paper serves as a useful reference for academic researchers and practicing engineers in the field of power converters and adjustable-speed drives. Index Terms--Current-source inverter (CSI), cycloconverter (CCV), high-power drives, load-commutated inverter (LCI).

This paper investigates the effects of grid voltage distortions caused by thyristor converters on the steady-state performance of a pulsewidth modulation (PWM) rectifier with dc voltage link for low-voltage applications. The disturbance transfer function of the current control loop is used to analyze the effects of grid distortions. Influences of the current controller, the phase-locked loop parameters, and the filter inductance on the generated current harmonics are presented. For existing grid voltage harmonics, the amplitude of the corresponding current harmonics are determined and compared to measured current harmonics using a 400-V 40-kW test bench consisting of a PWM rectifier with voltage dc link parallel to a 40-kW thyristor converter. Index Terms--Harmonic distortion, pulsewidth modulation (PWM) active front ends, thyristor converters.

This paper presents a technology review of voltage-source-converter topologies for industrial medium-voltage drives. In this highly active area, different converter topologies and circuits have found their application in the market. This paper covers the high-power voltage-source inverter and the most used multilevel-inverter topologies, including the neutral-pointclamped, cascaded H-bridge, and flying-capacitor converters. This paper presents the operating principle of each topology and a review of the most relevant modulation methods, focused mainly on those used by industry. In addition, the latest advances and future trends of the technology are discussed. It is concluded that the topology and modulation-method selection are closely related to each particular application, leaving a space on the market for all the different solutions, depending on their unique features and limitations like power or voltage level, dynamic performance, reliability, costs, and other technical specifications. Index Terms--High-power applications, multilevel converters, voltage-source inverters (VSIs).

This paper compares the expense of power semiconductors and passive components of a (2.3 kV, 2.4 MVA) two-level, three-level neutral-point-clamped, three-level flying-capacitor, four-level flying-capacitor, and five-level series-connected H-bridge voltage source converter on the basis of the state-of-the-art 6.5-, 3.3-, 2.5-, and 1.7-kV insulated gate bipolar transistors for industrial medium-voltage drives. The power semiconductor losses, the loss distribution, the installed switch power, the design of flying capacitors, and the components of an LC sine filter for retrofit applications are considered. Index Terms--Filter design, medium voltage, multilevel converters, power electronics.

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.

The design of a power converter must guarantee that the operating junction temperatures [V.sub.j] of all devices do not exceed their limits under all specified operating conditions. Usually, this is ensured by a simulative or analytical junction temperature estimation based on simple electrical and thermal models and semiconductor datasheet values. This paper discusses the difficulties and quantifies the limitations of this approach on the example of a three-level neutral point clamped voltage source converter (NPC VSC) with insulated gate bipolar transistors. The calculations are compared to the results of direct junction temperature measurements with an infrared camera. The paper also provides the experimental proof for the unequal loss and junction temperature distribution in the three-level NPC VSC. Index Terms--Insulated gate bipolar transistors (IGBT), Junction temperature measurement, neutral point clamped voltage source converter (NPC VSC), thermal modeling.

The low-frequency line transformer in todays ac rail vehicles suffers from poor efficiency and a substantial weight. Future traction drives may operate directly from the mains without this transformer. A feasible concept for a transformerless drive system consists of series connected medium voltage converters applying modern high-voltage insulated gate bipolar transistors (HV-IGBTs). In a first design step, the switching characteristics and losses of 6.5-kV IGBTs are compared to 3.3-kV and 4.5-kV IGBTs which are already commercially used in traction applications. Based on the considered HV-IGBTs, the properties of multilevel converters are analyzed and their applicability to the transformerless system is evaluated. The paper focusses on a loss analysis of the converters. Reliability aspects and harmonic spectra are briefly discussed. Taking these design aspects into account, the three-level neutral point clamped converter turns out to be a reasonable solution to realize line and motor converter modules in a transformerless traction system. Index Terms--Flying capacitor (FC) converter, gate turn-off thyristors (GTOs), high-voltage insulated gate bipolar transistors (HV-IGBTs), neutral point clamped (NPC) converter.

The three-level neutral-point-clamped voltage-source converter (NPC VSC) is widely used in high-power medium-voltage applications. The unequal loss distribution among the semiconductors is one major disadvantage of this popular topology. This paper studies the loss distribution problem of the NPC VSC and proposes the active NPC VSC to overcome this drawback. The switch states and commutations of the converter are analyzed. A loss-balancing scheme is introduced, enabling a substantially increased output power and an improved performance at zero speed, compared to the conventional NPC VSC. Index Terms--Medium voltage, power losses, three-level converter, voltage-source converter (VSC).

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.

This paper evaluates the benefits of three-level topologies as alternatives to two-level topologies in low-voltage converters primarily operated in rectifier mode. The main evaluation aspects are input filter size, semiconductor losses, maximum switching frequency, part count, initial cost, and life cycle cost. Semiconductor loss characteristics of various three-level topologies are discussed. A detailed converter comparison is based on a 100-kW 400-[V.sub.rms] rectifier using commercially available Si insulated gate bipolar transistor modules. Index Terms--Filter, losses, multilevel converter, rectifier.

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 a matrix converter (MC) and a dc-voltage link converter with an active front end for a 7.5-kW, 460-V induction motor drive. Part count, semiconductor losses, input filter design, and protection aspects are discussed. It is shown that the matrix converter's semiconductor losses are smaller only at full load operation for the same silicon area in both converters. A 33 % reduction of the device current rating of the MC is possible, resulting in comparable thermal device stress. The overall passive component count and rating is only slightly better for the MC. Index Terms--AC motor drives, input filter design, matrix converter, semiconductor losses, voltage-source converter.

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.

The introduction of new high power devices like integrated gate commutated thyristors (IGCTs) and high voltage insulated gate bipolar transistors (IGBTs) accelerates the broad use of pulse width modulation (PWM) voltage source converters in industrial and traction applications. This paper summarizes the state-of-the-art of power semiconductors. The characteristics of IGCTs and high voltage IGBTs are described in detail. Both the design and loss simulations of a two level 1.14 MVA voltage source inverter and a 6 MVA three-level neutral point clamped voltage source converter with active front end enable a detailed comparison of both power semiconductors for high power PWM converters. The design and the characteristics of a commercially available IGCT neutral point clamped PWM voltage source converter for medium voltage drives are discussed. Recent developments and trends of traction converters at dc mains and ac mains are summarized. Index Terms--Insulated gate bipolar transistor, integrated gate commutated thyristor, power semiconductor, pulse width modulated inverter, traction 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]

This paper describes the operation of modular multilevel converter, an emerging and highly attractive topology for medium- and high-voltage applications. A new pulsewidth-modulation (PWM) scheme for an arbitrary number of voltage levels is introduced and evaluated. On the basis of this PWM scheme, the semiconductor losses are calculated, and the loss distribution is illustrated. [ABSTRACT FROM AUTHOR]

This paper describes the parallel connection of 4.5 kV integrated gate commutated thyristors (IGCTs) and diodes. The impact of varying device characteristics on the stationary current distribution of parallel connected semiconductors is investigated. Possible solutions to improve the current sharing at steady state are presented. A thermal stabilization effect of parallel connected IGCTs is discussed. Furthermore, the behavior of parallel connected devices during switching transients is investigated experimentally in a 1.5.kV, 5-kA buck converter. Especially, the impact of asymmetrical circuit layouts, magnetic couplings, different turn-ON and turn-OFF delays, and junction temperatures are considered. It is shown that a substantial current derating is necessary to enable a reliable operation of parallel IGCTs and diodes. [ABSTRACT FROM AUTHOR]

This paper, along with an earlier published paper as Part 1, provides a comprehensive review of the state of the art of high-power converters (above 1 MW) for adjustable-speed ac drives. In this highly active area, different converter topologies have been developed for various drive applications in the industry. Due to its extensive coverage, the subject is divided into two parts: multilevel voltage source and current source converter topologies. This paper is focused on the second part and covers the current source converter technologies, including pulsewidth-modulated current-source inverters (CSIs) and load-commutated inverters. In addition, this paper also addresses the present status of the direct converter, which is also known as cycloconverter (CCV). This paper focuses on the latest CSI and CCV technologies and an overview of the commonly used modulation schemes. It also provides the latest technological advances and future trends in CSI- and CCV-fed large drives. This paper serves as a useful reference for academic researchers and practicing engineers in the field of power converters and adjustable-speed drives. [ABSTRACT FROM AUTHOR]

Active three-phase pulsewidth-modulated rectifiers are connected to the grid by an inductance or an LCL filter. Although an LCL filter is more effective since it more efficiently attenuates the switching harmonics, it causes stability problems. To enable a stable operation, either a damping resistor or an active damping (AD) algorithm has to be used. However, while a damping resistor causes additional losses, an AD algorithm usually requires extra sensors. To avoid these disadvantages, this paper shows simulation and experimental results of a simple ac voltage sensorless AD solution that is suitable for industrial applications. [ABSTRACT FROM AUTHOR]

The low-frequency line transformer in todays ac rail vehicles suffers from poor efficiency and a substantial weight. Future traction drives may operate directly from the mains without this transformer. A feasible concept for a transformerless drive system consists of series connected medium voltage converters applying modern high-voltage insulated gate bipolar transistors (HV-IGBTs). In a first design step, the switching characteristics and losses of 6.5-ky IGBTs are compared to 3.3-kV and 4.5-kV IGBTs which are already commercially used in traction applications. Based on the considered HIV-IGBTs, the properties of multilevel converters are analyzed and their applicability to the transformerless system is evaluated. The paper focusses on a loss analysis of the converters. Reliability aspects and harmonic spectra are briefly discussed. Taking these design aspects into account, the three-level neutral point clamped converter turns out to be a reasonable solution to realize line and motor converter modules in a transformerless traction system. [ABSTRACT FROM AUTHOR]