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Electromagnetic compatibility (EMC) filters are typically included in offline power converters, controlling electromagnetic emissions, but adding volume to power electronic systems. During the last decades, one of the main objectives of the power electronics industry has been the increase of the power density. Thus, it is reasonable to analyze how filters affect power density values, imposing limits or 'barriers' to it. The impact of the EMC filters on the overall volume of three-phase pulsewidth modulation (PWM) converters is studied here for converters in the range of 5-10 kW. An analytical procedure based on the volume minimization of the EMC filters is proposed to estimate the total filter volume as function of the converters' rated power and switching frequency. With this, the minimum volume for EMC filters that allow the converters to comply with EMC standards regarding conducted emissions can be estimated and volume limitations identified. A discussion about the limits of power density for the considered three-phase PWM converters for state-of-the-art power semiconductors is performed, and optimum switching frequencies are identified. An experimental verification is carried out, which validates the achieved results. Index Terms--Electromagnetic compatibility (EMC) filters, power density, sparse matrix converter (SMC), three-phase pulsewidth modulation (PWM) converters, Vienna rectifier.

Techniques have been presented in the literature for canceling stray capacitances for inductors in single-phase power filters. With the same aim, the alternatives provided by three-phase systems are explored here. A thorough theoretical analysis is presented, where pros and cons of parasitic capacitance cancellation networks are highlighted and improvements are proposed. A systematic mathematical procedure to evaluate impedances for different noise modes in three-phase circuits is presented. The influence of parasitic effects is accessed and asymmetric capacitance cancellation is proposed, facilitating applications in switched power circuits. Experimental results are shown demonstrating the effectiveness of the presented techniques in an electromagnetic compatibility filtering application. Index Terms--Parasitic capacitance cancellation, three-phase power line filters, three-phase networks.

The modeling and control of a three-phase three-switch buck-type rectifier system with integrated boost output stage (Voltage Range Extended 4-Switch Rectifier) is analyzed in this paper. A cascaded multiloop control structure is presented that has the following features: constant output voltage for a wide input voltage range and stepwise changes of load; sinusoidal input currents in phase with the mains voltages that also remain sinusoidal in case of unbalanced mains conditions; and active damping of the input filter resonance. For the control design, an equivalent dc-dc small-signal model of the converter is derived and verified by simulations and measurements. Based on this and on the identification of the critical operating point, the controllers for the inner dc current and outer voltage control loops are selected. The stability of the closed loop system is discussed and the robust operation of the system is verified by measurements on a 5-kW prototype. Index Terms--Robust control, small-signal model, three-phase pulsewidth modulation (PWM) rectifier, unbalanced mains conditions.

The digital control of a three-phase three-switch buck-type rectifier system is analyzed in this paper. Three main sources of time delays in the control loop can be identified for the implementation on a digital signal processor (DSP): 1) the delay time due to the sampling of the control quantities; 2) the one due to the calculation time of the DSP; and 3) the one due to the sample-and-hold function of the pulsewidth modulator. Using the buck-type system as an example, the influence of the time delay on the stability of the inner current control loop is discussed, and two prediction methods for time-delay compensation, i.e., a linear prediction and the Smith prediction, are comparatively evaluated. The control performance and the effect of the delay times and the prediction methods are shown by simulation results and through measurements on a 5-kW prototype. Index Terms--Digital control, prediction techniques, pulsewidth modulation (PWM) rectifier, time-delay compensation.

For a three-phase buck-type pulsewidth modulation rectifier input stage of a high-power telecommunications power supply module, a differential-mode (DM) electromagnetic compatibility (EMC) filter is designed for compliance to CISPR 22 Class B in the frequency range of 150 kHz-30 MHz. The design is based on a harmonic analysis of the rectifier input current and a mathematical model of the measurement procedure including the line impedance stabilization network (LISN) and the test receiver. Guidelines for a successful filter design are given, and components for a 5-kW rectifier prototype are selected. Furthermore, formulas for the estimation of the quasi-peak detector output based on the LISN output voltage spectrum are provided. The damping of filter resonances is optimized for a given attenuation in order to facilitate a higher stability margin for system control. Furthermore, the dependence of the filter input and output impedances and the attenuation characteristic on the inner mains impedance are discussed. As experimentally verified by using a three-phase common-/Differential-Mode separator, this procedure allows accurate prediction of the converter DM conducted emission levels and therefore could be employed in the design process of the rectifier system to ensure compliance to relevant EMC standards. Index Terms--Electromagnetic compatibility (EMC), input filter design, pulsewidth modulation (PWM) rectifier, test receiver.

Maximum power point tracking (MPPT) techniques extract the ultimate power from the photovoltaic (PV) source. Therefore, it is a fundamental control algorithm in any PV configuration. The research in this area is rich and many MPPT methods have been presented in the literature. However, in the current study, we focus on the PV model-based MPPT algorithms. In this regard, the classification of this category can be mainly divided into curve fitting methods and techniques based on the mathematical model or characteristics of the PV source. The objective of the PV model-based MPPT algorithm is to allocate the position of the maximum power point (MPP). Thus, no searching efforts are required to capture that point, which makes it simple and easy to implement. Consequently, the aim of this study is to give an overview of the most commonly utilized model-based MPPT methods. Furthermore, discussion and suggestions are also addressed to highlight the gap in this area. The main methods from the literature are compared together. The comparison and evaluation are validated using an experimental hardware-in-the-loop (HIL) system, where high efficiency (more than 99%) can be obtained with a simple calculation procedure and fast convergence speed. [ABSTRACT FROM AUTHOR]

The braking energy in diesel-electric locomotives is typically wasted into resistors. A more energy-efficient way is to store and recycle such energy. Thus, this article proposes a multiport power conversion system as the core of a hybrid energy storage system, based on Lithium-ion (Li-ion) batteries and supercapacitors (SCs). In such configuration, SCs act as a buffer against large magnitudes and rapid fluctuations in power, thus reducing current stresses in the battery system. Unlike other alternatives, this solution uses the recovered energy to supply only auxiliary loads, while the diesel generator keeps powering traction motors. As a consequence, the required energy storage capacity for the system is considerably reduced, which reflects reduced cost and volume. Further, the proposal can be used to retrofit existing systems and can also be adapted for other types of locomotives. To validate the proposed concept, a 7.6-kW scaled-down prototype was implemented using electric motors to emulate the locomotive power-train structure. Experimental results demonstrate the effectiveness of the power management strategy under different operating scenarios. [ABSTRACT FROM AUTHOR]

In an ideal ac–dc five-level current source multilevel converter, the dc current is equally divided between the two converters connected in parallel. However, current imbalances occur due to the nonidealities of the system, making the current balancing control to improve the multilevel converter performance. This article proposes two different methods for dc current balancing control for a five-level current source rectifier using an advanced carrier-based modulation strategy implemented through three different modulation patterns. A 6-kW prototype is constructed to demonstrate the current balancing control and a comparison among the methods is presented. [ABSTRACT FROM AUTHOR]

Even though multipulse rectifiers (MRs) are a long established and well-known technology, still their behavior is not fully described in the literature when they are fed by three-phase balanced sinusoidal currents sources. To address the aforementioned gap, this paper presents the operation and properties of current-fed MRs. The undertaken aim is achieved by analyzing the examined topology through circuit analysis and then, the theoretical results are validated through comparisons with the simulated waveforms and experimental results. Furthermore, the expected harmonic content and the duality with traditional voltage-fed MRs (VFMRs) are presented. In the proposed structure, the transformer voltages present a multipulse waveform, instead of its primary currents as in VFMRs. This implies on limiting the voltage steps and its derivative, which might be beneficial to reduce cost and volume of insulation, particularly for MVDC and HVdc applications. Besides that, by actively controlling the primary currents, a possible copper loss reduction is shown in the transformer windings, differentiating the proposed structure from its voltage controlled counterpart. [ABSTRACT FROM AUTHOR]

This letter proposes a closed-form solution for core loss computation exemplarily for the boost inductor of a single-phase power factor correction boost bridgeless converter. The core loss calculation is based on the improved generalized Steinmetz equation (iGSE) method, which consists in the separation of the contributions of major and minor loops in the B–H curve. However, the computational procedure based on loop separation routine of the iGSE is replaced here with an integral-based computation. This leads to the advantage that the resulting expressions are in a closed form that is suitable for optimization routines. The proposed method can be extended to other converters. Three different design results are compared with two standard numerical iGSE routines, one made by the authors and the original routine made by the iGSE authors. Experimental results for a fourth case are presented. The importance of modeling the major loop losses is also discussed. [ABSTRACT FROM AUTHOR]

With the growing interest of the industry in high-power medium-voltage multilevel inverters and the technological limitation in high voltage power semiconductors switches, synchronous optimal pulse width modulation techniques, originally developed for two-/three-level inverters, became again a topic of interest, now to optimize multilevel waveforms. This work proposes a novel formulation for the problem of optimizing the modulation pattern of multilevel converters, including in a single optimization problem the decision of the directions for each step transition in addition to the switching angles and, thus, completely defining the optimized multilevel waveform at a given modulation index. In addition, experimental results are presented in order to demonstrate the effectiveness of this optimized modulation technique exemplar applied to a five-level NPC H–bridge feeding a permanent magnet synchronous motor. [ABSTRACT FROM AUTHOR]

This paper analyzes three different carrier-based modulation patterns applied to a three-phase high-power-factor-corrected (PFC) five-level buck+boost-type converter acting as an interface between dc distribution systems and an ac grid. The modulation is analyzed employing the space vectors theory so that the achievable performance is demonstrated. The main advantage of the analyzed modulation strategy is its simplicity, which makes it suitable for digital signal controller (DSC) implementations. This seems straightforward for voltage source converters, but is a challenge for current-multilevel converters that typically employ field-programmable gate array devices to achieve better harmonic distortion performance. This is due to modern power electronics DSCs being typically designed for other converter topologies. The power converter is constructed with two phase-shift-modulated six-switch buck-type PFC converters, paralleled by interphase transformers, and an inverting circuit. The system features: bidirectional current carrying capability; relatively low parts count; high utilization of the semiconductors; and low current and voltage ripple at its terminals. The principle of operation, detailed description, analysis of the modulation strategy, and dimensioning equations for three different power circuit realizations are described in this paper assuming the analyzed modulation patterns. The feasibility of the presented converter is demonstrated by means of a constructed hardware prototype. [ABSTRACT FROM AUTHOR]

Alternating current (ac) active electronic loads (AELs) based on pulsewidth modulation (PWM) converters, capable of emulating nonlinear loads, require effective current control techniques and power stages. These two aspects of an AEL are interdependent mainly due to the presence of electromagnetic compatibility filters to reduce electromagnetic emissions. However, the filter components affect the dynamics of the system. In this context, this paper proposes a digitally implemented control strategy comprising the state feedback, robust observer, phase-locked loop, and linear current controller to cope with ac AEL applications. The control-oriented modeling and the control system design are presented. Experimental results obtained from a 10-kW three-phase three-level PWM converter prototype illustrate and demonstrate the feasibility of the proposed AEL control strategy. [ABSTRACT FROM PUBLISHER]

Novel simple indirect control concepts for an active power filter (APF) application are proposed here. The concepts are exemplarily presented to control a modified APF structure. The main advantage over other control strategies is the achieved excellent simplicity-to-performance ratio. The proposed control strategies are based on the concept of virtual impedance emulation to provide high power factor in a system. To validate the operating principle, a single-phase low-power prototype has been built and experimentally tested. This prototype operates at a remarkably low switching frequency of 5 kHz and is digitally controlled by a digital signal processor. [ABSTRACT FROM PUBLISHER]

A novel three-phase hybrid multilevel converter is proposed for medium-voltage applications. The converter employs a conventional three-phase voltage source inverter (VSI) linking series connected half-bridge modules at each phase. With the proposed connection, a large portion of energy can be processed by the VSI by employing a single multi-pulse rectifier, while smaller power shares are processed within the half-bridge modules. Thus, the requirements for galvanically insulated dc sources are reduced. Modularity is naturally achieved. A modulation scheme for a four-level version is proposed and analyzed in detail. This scheme allows unidirectional power flow in all dc sources and, consequently, enables diode bridges to be employed in the rectification input stage for unidirectional applications. [ABSTRACT FROM PUBLISHER]

This paper presents a comprehensive physical characterization and modeling of the three-phase common-mode (CM) inductors along with the equivalent circuits that are relevant for their design. Modeling issues that are treated sparsely in previous literature are explained in this paper, and novel insightful aspects are presented. The calculation of the leakage inductance is reviewed, along with the magnetic core saturation issues, and a new expression for the leakage flux path is derived. The influence of the core material characteristics on the performance of the component is discussed, and a new method for the selection of the material for the minimized volume CM inductors is proposed in order to simplify the design procedure. Experimental results which validate the model are presented. [ABSTRACT FROM PUBLISHER]

Novel symmetric hybrid multilevel topologies are introduced for both single- and three-phase medium-voltage high-power systems. The topology conception is presented in detail, where a three-level switching cell with low component count, and its modulation pattern give the origin of the proposed converters. Voltage sharing and low output-voltage distortion are achieved. The theoretical frequency spectra are derived. Switching devices are separated into high- and low-frequency devices, generating hybrid converters. Five-level three-phase topologies are generated from only three insulated dc sources, while the number of semiconductors is the same as for the cascaded H bridge. Both simulation and experimental results are provided showing the validity of the analysis. [ABSTRACT FROM AUTHOR]

This paper presents a study and practical implementation of an active filter employing a high-frequency (HF) power amplifier and passive-filter components to be connected to the ac power lines in order to mitigate common-mode conducted emissions of three-phase pulsewidth modulation converter systems. The filter topology is chosen from different possibilities listed in a literature survey and studied regarding practical implementation issues, where requirements for an HF power amplifier to be applied in active filtering are derived. Special attention is put on the stability analysis where the challenges for the feedback are discussed, and a simple feedback structure is proposed. Other feedback concepts are analyzed, and limitations posed by stability requirements are presented. A prototype is designed and built, from which mathematical and experimental results are obtained demonstrating the potential and limitations of such a system. [ABSTRACT FROM AUTHOR]

This paper presents the study of a dc-dc buck converter with three-level buck clamping (buck-buck), zero- voltage switching (ZVS), active clamping, and constant-frequency pulsewidth modulation (PWM). Other ZVS dc-dc converter topologies that employ three-level switching cells are introduced, and their steady-state dc gain is analyzed. This analysis shows that the buck-buck converter has characteristics that warrant a more detailed study. A feature that is common to all the introduced topologies is the theoretical reduction of the voltage stresses across the active semiconductors to 50% of the corresponding two- level converters. Accordingly, the switches of the buck-buck converter provide 50% of the blocking voltage of a ZVS two-level buck converter. The steady-state analysis of the converter is performed according to the description of the operation stages of the converter. Based on the performed analyses, a comparative discussion to other topologies is given. Furthermore, a topologic derivation of the circuit is presented, which provides ZVS operation to all semi- conductors. Finally, a simplified design procedure is proposed, and used to design and build a prototype. Experimental results from a laboratory prototype are presented. [ABSTRACT FROM AUTHOR]

• Control strategy for mitigating the synchronous generator fault current • Control guarantees a decrease in the current amplitude beyond sub-transient period • Form of protection in case of a protection system failure • Helps on the immediate recovery of the post-fault system • The strategy can reduce costs to over-sizing the protection system The fault protection devices that are used in high power isolated power systems require attention because of the high current levels. Such installations might benefit if their short-circuit current levels are reduced by control, rather than by inserting series impedance to the generators that would otherwise worsen regulation and increase size. This work proposes a strategy for controlling the fault current by actuating on the excitation system of a synchronous generator. The aim is to reduce fault levels during, both, transient and steady-state. The proposed strategy utilizes an adaptive algorithm working as an optimal model-based controller with current feedback, whenever a fault is detected and until its clearance. The used methodology comprises the modeling of the synchronous generator, as well as of the main sub-elements that are dynamically involved in the system, namely the exciter and the gas turbine models. The analyzes and simulations results are obtained for a round-rotor synchronous generator with a nominal power of 31.25 MVA. The proposed strategy effectively reduces the fault current amplitudes during transient dynamics compared to the system operating with a typical automatic voltage regulator (AVR). [ABSTRACT FROM AUTHOR]