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Many research works report the use of LCL filters for grid-interfaced PV systems. Indiscreet selection of passive LCL filter parameters may result in poor filtering and increased power losses. LCL filter parameter selection is critical to get a good performance and at the same time ensure that losses and costs stay low. This paper proposes a novel approach to design the LCL filter for a grid-interfaced PV system. A cost-based minimization approach on a cost per joule basis for each of the filter elements is explored to obtain the optimal filter design. Simulation results for a 10-kVA grid-connected inverter with an LCL filter are presented in order to verify the efficacy of the proposed design. The impact of designed filter parameters on the ripple current is also discussed in this paper. The total inductance of the LCL filter is varied and filter parameter values which give lowest cost is identified while meeting harmonic standard requirements and the fundamental voltage drop across the filter. Finally, the proposed design is also experimentally validated via a hardware prototype. Results validate the design method in terms of the harmonic attenuation and total harmonic distortion. [ABSTRACT FROM AUTHOR]

This paper proposes an online condition monitoring system for aluminum electrolytic capacitors used as dc-link capacitors in industrial power converters. Electrolytic capacitors are one of the most fragile components of a power converter system because of their wear-out failures and short lifespan. Therefore, the use of condition monitoring systems for aluminum electrolytic capacitors allow preventive maintenance to be performed, thereby avoiding unexpected shutdown and downtime. The dominant wear-out mechanisms in aluminum electrolytic capacitors are characterized by the increase in equivalent series resistance. Hence, the condition monitoring system proposed in this paper is based on the online estimation of the capacitor's equivalent series resistance using the switching frequency components of the dc-link capacitor voltage and current. The equivalent series resistance estimation method is tested using the PSpice circuit simulator and is validated experimentally using a custom-made inverter. Finally, the equivalent series resistance estimation method is adapted for the condition monitoring of capacitors in industrial power converters and the proposed condition monitoring system is implemented in a commercial ac drive system to prove the applicability of the proposed method to industrial power converters. [ABSTRACT FROM AUTHOR]

A breaker-less shipboard medium-voltage dc (MVDC) system is gaining more attention recently due to its advantage in dealing with a dc fault by using switched-mode power modules and disconnectors. The specific power module investigated in this paper is the power conversion module (PCM) that transforms power from a MVDC to a low-voltage dc (LVDC) bus. The PCM plays an important role in a system-level fault management. The recently emerging isolated modular multilevel dc/dc converter and the widely used dual active bridge converter are promising solutions for PCM applications. The control algorithms including fault protection strategy for both topologies have been developed and presented in this paper. The MVDC side fault and LVDC side fault of each topology has been analyzed and evaluated. The simulation and experimental results are provided to demonstrate the fault protection features of two topologies in a breaker-less dc system. [ABSTRACT FROM AUTHOR]

Three instruments have been evaluated for their ability to estimate the load conditions and efficiency of operating motors based solely on measurements of terminal voltage and current. Laboratory tests, compared to a high-accuracy dynamometer system were used to assess the instruments' accuracy. Field tests were conducted in a paper mill to determine the ease of use and lack of intrusion. In both laboratory and field tests the instruments were applied to 50-hp, 100-hp, and 200-hp 460-V induction motors. Data of the relative accuracies of the three instruments, as functions of motor load and supply voltage, are presented together with observations of ease and lack of intrusion in use. [ABSTRACT FROM AUTHOR]

The conservative power theory (CPT) is a time-domain theory applicable to any periodic signal single- or polyphase system with or without a neutral conductor. The principle operation is the orthogonal decomposition of electrical variables, resulting in electrical quantities with physical meaning. An important feature of the CPT is the current decomposition. It consists of decomposing any current into five parts. The label of these parts is active current, reactive current, scattered active current, scattered reactive current, and generated current. This paper proposes the application of the current decomposition of the CPT in distributed energy resources (DERs). A supervisory controller (SC) uses the current decomposition in a load power-sharing strategy. The combination of these two issues is the main contribution of this paper. Moreover, the proposal of this paper is more attractive than the conventional droop strategy since the DERs follow their current reference in a current-controlled mode, making the load sharing faster, more reliable, and more accurate. A clear understanding of how the CPT decomposes load currents into its parts is presented, as well as the drawback found in droop strategy when dealing with load power sharing. Later, the SC load power-sharing strategy is described, indicating that the proposal of this paper makes an SC to have a broad option when managing a smart grid with dispatchable DERs. A case study with experimental results shows the efficacy of applying current decomposition of the CPT in load power-sharing strategies. [ABSTRACT FROM AUTHOR]

The next big change in various industry applications is associated with power dense motors, such as permanent magnet synchronous motors (PMSMs). Utilization of multiphase PMSM can offer an additional fault-tolerant capability to their applications. Combining both advantages, this paper proposes a simple yet robust current control strategy for a five-phase PMSM under normal operation and in a case of a loss of one phase. Traditional linear current controllers successfully applied to reference tracking of a healthy motor may become less efficient during postfault operation due to additional unmodeled dynamics. This paper proposes a modified angular transformation to a special rotating frame in which the postfault permanent magnet flux linkage remains unchanged and the motor model remains decoupled. Following this, a nonlinear current control scheme based on sliding mode control is proposed, which successfully treats model inaccuracies and provides good dynamic performance and tracking accuracy. Feasibility of the proposed control strategy is experimentally validated on a laboratory scale PMSM motor with a digital signal processor/field programmable gate array based drive. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the behavior of electromagnetic forces during the occurrence of faults inside transformers as result of transients in the electrical systems. The methodology is based on the modeling of a single-phase 50-MVA transformer subjected to inrush currents through finite-element method. In this perspective, the values of inrush currents, obtained by the alternative transient program software, are used to estimate the magnetic field density dispersion in the transformer, and to find the values of forces in axial and radial directions. These forces components are distributed along the energized windings for observing the loads behavior in high-voltage windings. This paper will thus present investigations of electromagnetic forces, structural deformation, stresses, and safety factor on transformer's winding when subjected to inrush current. [ABSTRACT FROM PUBLISHER]

This paper presents the flexible dc capacitor voltages balancing control method for star-connected cascaded H-bridge converters. In this paper, the power flows are analyzed by investigating all the converter's control freedoms. Based on the analyses, users can accomplish the dc capacitor voltage balancing with both negative-sequence current and zero-sequence voltage. These two kinds of control options are further integrated together with the defined weighting factor $K$. The low-voltage ride-through operation of a proposed control method is also discussed in this paper. The control method is verified with a 220-V 1-kVA static synchronous compensators based on the star-connected cascaded H-bridge converters, and the experimental test results show that all the dc voltages are well regulated at the commanded value with different weighting factor $K$. [ABSTRACT FROM AUTHOR]

In this paper, a new generic composite load model structure for industrial facilities is proposed, which consists of four main loads, an induction motor, a synchronous motor, a motor drive system, and a static load. This structure can be applied to existing or future industry facilities. Major factors to be considered when developing this new composite load model are demonstrated. To achieve the final composite load model for an industrial facility of interest, a two-step procedure is recommended in this paper. Step 1 is to create a power system full model for existing or future industrial facilities. In this step, the full model for existing facilities can be created with the known system configurations and electrical single-line diagrams; while the full model for future industrial facilities with unknown system configurations can be created using the template-based load modeling technique. Step 2 is to perform effective load aggregation in order to obtain a simplified equivalent load model in the format of the proposed composite load model structure for industrial facilities. [ABSTRACT FROM AUTHOR]

This paper presents the development of detailed simulation models to study short-circuit protection of on-board dc auxiliary systems in a rapid transit train. As the investigation of protection solutions during the testing phases is costly, it is necessary to perform detailed protection analysis earlier in order to detect potential protection issues. This requires modeling the behavior of batteries, auxiliary converters, and the detection and arcing mechanisms of protection devices in detail, as shown in this paper. The protection device under consideration in this study is the molded-case circuit breakers (MCCBs) equipped with adjustable thermomagnetic trip unit which are widely used in the railway industry. To maintain battery system availability, they are selected, sized, and adjusted to avoid false tripping during emergency conditions. However, they must also be sensitive enough to detect the limited available fault current which is specific to rapid transit train dc auxiliary systems. Tolerances on the detection time of thermomagnetic units may be unacceptable as shown in this study. In order to overcome this problem, electronic trip unit assistance to conventional thermomagnetic-type MCCBs is proposed and the requirements for such a device are evaluated using the detailed simulation platform. [ABSTRACT FROM AUTHOR]

This paper presents the stability analysis of dc distributed power systems with multiple converter-controlled loads. The load converters are tightly controlled, behaving as constant power loads with low-damped $LC\;$ filters. The dynamic behavior of the system in high frequency range is often not studied with the classical tools based on conventional averaging techniques. However, dc power systems with the reduced size filter, and consequently, the high resonant frequency, are widely used in transportation applications. In this paper, the stability analysis of the system is established based on a discrete-time model of the system, taking into account the switching frequency and intrinsic nonlinearities of the system model. The impacts of the filter parameters and interactions among the constant power loads are investigated with the proposed discrete-time method. Moreover, an active stabilizer is developed and included in the dynamic model of the system, in order to extend the stability margin. The theoretical observations are then validated experimentally on a laboratory hardware prototype. [ABSTRACT FROM AUTHOR]

Renewable power plants must comply with certain codes and requirements to be connected to the grid, being the ramp-rate compliance one of the most challenging requirements, especially for photovoltaic or wind energy generation plants. Battery-based energy storage systems represent a promising solution due to the fast dynamics of electrochemical storage systems, besides their scalability and flexibility. However, large-scale battery energy storage systems are still too expensive to be a mass market solution for the renewable energy resources integration. Thus, in order to make battery investment economically viable, the use of second life batteries is investigated in the paper. This paper proposes a method to determine the optimal sizing of a second life battery energy storage system (SLBESS). SLBESS performance is also validated and, as an ultimate step, the power exchanged with the batteries is calculated during one-year operation. The power profile obtained is further used to define the cycling patterns for laboratory testing of second life batteries and to study their ageing evolution when used for the power smoothing renewable integration application. Real photovoltaic energy generation data from a Spanish plant were used for the study. [ABSTRACT FROM AUTHOR]

In the oil and gas industry, large synchronous motors are used to drive water injection pumps to support the pressure of a reservoir and to maintain the production level of a reservoir over a longer period. Therefore, failures in such motors will have an adverse impact on operation and production. Even though synchronous motors are superior to induction motors in relation to system voltage regulation and power factor correction, their starting is more complicated. As a result, the application of synchronous motors requires careful engineering analysis in the design stage of a project to determine system requirements for a successful operation. This paper presents a failure analysis case study for three 11 000-hp synchronous motors at a gas–oil separation plant along with the starting issues faced prior to the occurrence of a permanent damage. The fundamentals of dynamic motor acceleration requirements to achieve a successful start will be reviewed. In addition, results of site measurements and subsequent computer simulation will be presented. The simulation results were substantiated by a failure root cause analysis report provided by the manufacturer. This paper also discusses the obstacles faced as a result of erroneous and limited data availability, and the approach to overcome such difficulties. [ABSTRACT FROM AUTHOR]

This paper discusses incipient end-winding interturn faults in the stator winding of a permanent magnet synchronous motor caused by the mechanical vibrations of the concerned turns. With aging, the end-winding blocking system becomes weaker and turns insulation degrades until its breakdown. The fault is modeled by an intermittent interturn short circuit between the turns of the stator end winding. Intermittent fault occurrence disturbs the stator currents as well as the reference voltages leaving a specific fault signature. The detection method uses a pattern-adapted wavelet to detect fault occurrence. In this paper, it is applied to the quadrature reference voltage. Simulation and experimental results confirm the effectiveness of the proposed approach. [ABSTRACT FROM PUBLISHER]

This paper demonstrates practical considerations when studying overcurrent protection coordination in industrial systems and applying related IEEE Standards. This paper is divided into two parts. Part one focuses on protection coordination for high-voltage and medium-voltage industrial systems. Part two covers balance of distribution system topics. The main discussed subjects are time/chronologic, current/amperometric, as well as zone selective interlocking coordination. Other factors that affect coordination are also addressed. Suitable selections of the relay time–current characteristic are presented. This paper also includes practical details for accepted coordination time interval in coordinated systems. [ABSTRACT FROM PUBLISHER]

This paper was written to share the experience acquired in the specification of surge suppressors (snubbers) for protection against switching transients’ overvoltage resulting primarily in dry-type transformers failures in some plants in Brazil and North America. This paper will also explain about the snubber ratings (damping resistor, surge capacitor, and surge arrester), the assembly special cares, system modeling, and simulations using the software Alternative Transient Program. [ABSTRACT FROM PUBLISHER]

This paper presents a novel model predictive torque control with discrete duty ratio optimization for a six-phase PMSM machine with high robustness against weighting factor variation. First, a two-step lookup table is developed to initially select the optimal voltage vector, which is to regulate the torque and flux in the energy conversion related subspace, as well as suppress the harmonic currents in the x–y subspace. Then, a null vector is inserted along with the selected optimal voltage vector to adjust the duty ratio with a set of value to avoid the complicated derivation. Subsequently, the optimal duty ratio is determined by a cost function to minimize the torque and flux error. So by using the proposed method, the torque ripple is reduced and even applying an improper weighting factor will not deteriorate the machine performance severely. Finally, experimentations are carried out to verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

One of the benefits of double-circuit transmission lines is that line maintenance work can be performed on a de-energized circuit while the other circuit remains energized. However, induced voltages and currents can be generated on the de-energized line due to electrostatic and/or electromagnetic coupling effects and the close proximity to energized conductors. In order to mitigate the safety concern related to high induced voltages or currents, line discharging grounding switches (LDGS) may be installed. Since this can be an expensive solution, the magnitude of induced voltage and current is the key for defining safety criteria to judge whether or not a costly mitigation plan is needed. This paper presents the theory of induced voltage and current and a sensitivity analysis of influential parameters that impact each. In addition, a safety criterion using arc reach calculation is proposed to determine when LDGS are required. A case study is included. [ABSTRACT FROM AUTHOR]

This paper proposes a switching strategy for the Z-source inverter (ZSI), which has unequal short-through intervals to reduce the current ripple in the inductor of its impedance source. A size reduction of the inductor of the ZSI is one of the important issues in improving the power density of the ZSI, and the inductor current ripple reduction is required to achieve it. The proposed method can reduce the inductor current ripple by 27.8% compared with the conventional method that has equal short-through intervals without increasing the number of inverter switching. The proposed operation and ripple reduction were confirmed in experiments with a 3-kW-class laboratory prototype. Its result agreed to the calculated results, and it was confirmed that there is no increase in circuit losses caused by the application of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a new zero-sequence current suppression control strategy for the five-phase open-winding fault-tolerant fractional-slot concentrated-winding interior-permanent-magnet (FTFSCW-IPM) motor drive system with a common dc bus is proposed. By unequal distribution of the zero voltage vector, the proposed method can well suppress the zero-sequence current caused by the dead-time effect that the conventional eliminating method cannot be achieved. First, the dead-time effect to the zero-sequence current is discussed. Then the zero-axis controller is designed to obtain the reference common-mode voltage. Last, according to the principle of the unequal zero voltage vector distribution, the switching sequence of the two inverters can be calculated, and the maximum modulation index is also first deduced in detail. The proposed method is proved by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

A synchronous reluctance motor drive exhibits an inherent unlimited speed range capability; in fact, the maximum speed of this kind of machine is bounded only by mechanical limits. In order to exploit this peculiar characteristic of the drive while assuring the lowest power losses, a proper control algorithm has to be used. In particular, while the working speed is increasing, the control must be able to command the reluctance motor under the maximum torque per ampere condition at first, into the flux-weakening region, and then on the maximum torque per voltage trajectory. To this purpose, a novel voltage control loop is presented in this paper. It is combined with a field-oriented current control and profitably exploits a polar coordinate representation of the current reference to operate the reluctance machine in compliance with current and voltage rating constraints in all the different operating conditions. Additional merits of the proposed scheme are the ease of implementation and the simple design. The stability of the proposed control algorithm is proved through a small signal analysis and simulations and experimental tests confirm its effectiveness. [ABSTRACT FROM AUTHOR]

With the increase of the train speed, the pantograph-catenary (PC) detachment becomes more frequent, which results in more serious PC detachment arc. In order to analyze the influence of PC detachment arc on the train system, several arc models are established. However, these models do not consider the actual PC detachment process. In this paper, an extended black-box model of PC arc is proposed, which considers the dynamic detachment process of PC based on the PC dynamics. First, the Habedank arc model is presented and the relationship of the PC detachment distance with the arc voltage and arc dissipated power is established. Next, the dynamic detachment trajectory is obtained from the dynamic simulation of the PC structure model. Then, by introducing the dynamic PC detachment trajectory model into the arc model, the dynamic arc model is built. Finally, the performance of the arc current and arc voltage is analyzed and the effectiveness of the dynamic arc model is verified. [ABSTRACT FROM AUTHOR]

The use of energy harvesting for supplying wireless sensors becomes a new market opportunity. During last years, new low power transmitters, and also power conversion ICs specifically designed for energy harvesting, have become commercially available. However, as any other power supply circuit, the specific load behavior affects to the power converter, doing that just joining the two parts takes to a nonfunctional device. In this paper, we will measure experimentally the transmitter current of some technologies, for the several sensor states. Some practical issues that affect directly the sensor design will be shown. With this information, some required modifications in the power stage will be proposed. A complete temperature sensor design and assembly is showed. The sensor has been tested in a tandem cold mill, and several experimental results are included. [ABSTRACT FROM AUTHOR]

This paper presents an immune feedback control algorithm for a three-phase distribution static compensator (DSTATCOM) to mitigate several power quality problems such as harmonics, reactive power, and load unbalancing at distribution level. A configuration chosen for DSTATCOM is based on a three-phase voltage source converter (VSC), which is suitably controlled as a shunt compensator for performing these functions. The underlying principle of an immune feedback is based on adaptive control and the designed control estimates fundamental reference grid currents from nonlinear load currents. This control algorithm proposed for DSTATCOM, is validated for maintaining power factor to unity, load balancing, and harmonics reduction of supply currents. An improved performance of immune feedback control is presented along with its comparison with conventional control algorithms such as dq frame, normalized least mean square and other recently developed control algorithms such as leaky least mean square, leaky least mean fourth, and synchronous extraction. Experimental results are obtained with the proposed control, which is tested on a prototype developed in the laboratory using a VSC. It is observed from simulation and experimental results that the proposed control algorithm of DSTATCOM is able to achieve mitigation of most of the power quality problems at the distribution level. [ABSTRACT FROM AUTHOR]

This paper highlights the power quality issues and explains the remedial measures taken by means of hybrid front-end third harmonic current injection rectifiers. Here, a zig-zag transformer is used as the current injection device so that the advantages pertaining to the zig-zag transformer are effectively utilized. The third harmonic current injection device along with three-level boost converter at the output stage will increase the dc-link voltage. With less boost inductance, generally half of the conventional boost converter inductance is sufficient to implement the proposed converter structure resulting in reduced ripple current and also the device rating is reduced by half of the output voltage. Moreover, the power quality is well improved using third harmonic current modulated front-end structure, which is well appropriate for medium/higher power applications. The experimental prototype of hybrid front-end converter is developed in the laboratory to validate the MATLAB simulation results. [ABSTRACT FROM AUTHOR]

This paper presents a novel grid current control of a grid-connected voltage source converter with an LCL filter. The proposed control method uses an $\mathcal {H}_\infty$ synthesis method to shape the input admittance of the converter, to track a given current reference, and/or to limit the controller actuation at different frequency ranges. The converter admittance is shaped, both in magnitude and phase, following a model reference defined by the designer in the frequency domain. By specifying a low admittance magnitude reference, the optimization algorithm will obtain a controller that actively damp the filter resonance and attenuate/reject the grid voltage oscillations, either in a wide frequency range or concentrated at the main harmonic frequencies. Additionally, the proposed controller design methodology takes advantage of its admittance phase shaping capability to improve the system robustness in front of grid uncertainties and minimizing converter impact over grid stability due to its positive-real nature. The synthesized controller only measures the grid current and voltage to achieve the aforementioned results, reducing the number of sensors (and their associated cost) required for its implementation. Experimental results illustrate the correct behavior of the closed-loop system with the designed controller in time and frequency domain. [ABSTRACT FROM AUTHOR]

This paper discusses the energization and start-up process of modular three-stage solid-state transformers (SSTs) based on a cascaded H-bridge topology. A key element of the SST is the auxiliary power supply (APS) feeding the auxiliary circuitry. Redundancy and simpler implementation can be achieved by powering the APSs from the dc-link capacitors of cells, but at the expense of a more challenging start-up process of the SST. The first step of this process must be performed before APSs are operative. This can result in undesired transient events (inrush currents, voltage sags in the capacitors voltages, etc.), which could prevent a proper start-up of the SST or even jeopardize the power devices or other elements. A simple strategy for the energization and start-up of SSTs using this APS structure is proposed. The method is valid for both grid-forming and grid-feeding operations of the SST, regardless of the energization port and without the addition of any extra circuitry. Simulation and experimental results are provided. [ABSTRACT FROM AUTHOR]

Series-dc collection and transmission is suggested to be competitive for remote offshore wind farms. However, severe overcurrent, overvoltage, and other impacts that arise from faults cause challenges on system protection, which have not been fully studied yet. In this paper, simplified equivalent circuits are developed for fault analysis, based on which analytical models for fault transients are derived. The expressions can be used for stress estimation, as well as provide insight in understanding the mechanism of fault propagation. A cost-effective protection scheme characterized by a breakerless design is proposed. Parameter selection for stress mitigation is also discussed. Simulation results verify that the proposed fault protection and stress mitigation design is effective for such a series-dc system. [ABSTRACT FROM AUTHOR]

This paper investigates ac–dc–ac multilevel topologies for three-phase four-wire applications obtained from an interconnection of three-leg voltage-source converters. The topologies can be applied in line voltage regulators, universal active power filters, and uninterrupted power supplies. Operating principles, a pulsewidth modulation (PWM) technique, and an overall control strategy are developed. The PWM and control strategies are suitable to regulate the dc-link voltages and to reduce the harmonic distortion, switching stress, and power losses. Simulation results are used to compare the proposed configurations with a conventional solution in terms of harmonic distortion, semiconductor losses, and others characteristics. Experimental results are presented to validate the theoretical considerations and were obtained by using insulated-gate bipolar transistors with dedicated drives and a digital signal processor with appropriated plug-in boards and sensors. [ABSTRACT FROM AUTHOR]

Electrical power losses in distribution networks contribute significantly to the overall energy loss in power systems. Reducing network losses can help the power system become more energy efficient. The solid-state transformer (SST) is primarily being considered as a replacement to the traditional fundamental frequency transformer. This paper proposes the use of the dual-reactive power support feature of the SST to reduce radial distribution network losses. A planning algorithm using particle swarm optimization (PSO) is proposed to optimally locate and size the SST installations with an overall objective of reducing network losses. The proposed algorithm is implemented on a standard 33-bus radial distribution network and the results for multiple scenarios are presented. It is shown that by increasing the deployment of SST, the losses in the distribution network can be reduced considerably. [ABSTRACT FROM AUTHOR]

This paper investigates an ac–dc–ac multilevel power converter. The studied configuration is composed of two single-phase ac–dc–ac three-leg modules and series-connected H-bridges in the shared part of system. Because the proposed converter has shared legs between the input and output, it is employed in applications with same input and output frequency. Uninterrupted power supply and unified power quality conditioner are application examples for this converter. Such multilevel topology has lower dc-link voltage rating, which, consequently, presents low switch blocking voltages when compared to conventional topologies. System model, a space-vector pulsewidth modulation (PWM) strategy to symmetrical and asymmetrical dc-link voltages, and an overall control strategy to adjust the system variables are presented. A power flux analysis shows the operation zone in which the individual dc-link voltage balancing is possible. PWM and control strategies are developed to reduce the semiconductor total losses, harmonic distortion, and switching stress. Two ac–dc–ac multilevel conventional structures are used for comparison. Simulation and experimental results demonstrate the feasibility of the studied converter. [ABSTRACT FROM AUTHOR]

This paper presents a nine-level transformer-based inverter requiring only eight switches. The envisaged structure consists of two standard H-bridges fed from a single dc source. Besides, a single-phase transformer is employed to aid the process of intermediate voltage level generation. An ad-hoc pulsewidth modulation scheme based on boolean logic form equations is developed to derive the gating pulses. An effortless extension of the proposed inverter to a higher number of voltage levels is also achieved by generalizing the switching functions. Furthermore, the superior performance of the proposed topology is demonstrated through a comprehensive cost-based analysis. Finally, the validation of the proposed topology is accomplished through experiments on a down-scale prototype, and the measurement results are included. [ABSTRACT FROM AUTHOR]

This paper analyzes the influence of stator windings turn-to-turn fault on inverter-fed permanent magnet (PM) machines. By adding a secondary neutral point (NP) in stator windings, the turn fault detection and tolerant capability can all improve considering a small turn-to-turn short at an early stage. From the perspective on fault detection, the proposed windings with two NPs increase the equipment impedance per NP. Once a turn fault occurs, the fault-induced voltage harmonic magnitude increases. It results in a better signal-to-noise ratio for the fault detection. From the perspective on tolerant drive, the fault-induced circulating currents can flow across different phase coils in the windings with two NPs. Reduced effect on circulating currents in a faulty machine is achieved due to the current diversion. Turn fault induced additional losses are then decreased compared to conventional windings with only one NP. A 1-kW PM machine with two different windings is tested to verify the fault detection and tolerant performance. [ABSTRACT FROM AUTHOR]

This paper presents a system that enables the passive reduction of noise and vibrations in a three-phase induction machine with a stator damper winding connected to capacitors. This is a simple and effective system for reducing the flux density harmonics in an electrical machine. The theoretical study is based on the modeling of a machine equipped with the damper winding obtained from Kron's theory about equivalent circuits of electrical machinery. The analysis of the equivalent circuit allows one to identify possibilities to reduce the flux density harmonics responsible of unwanted noise and vibration components. Finally, an experimental validation is performed. [ABSTRACT FROM AUTHOR]

DC solid-state circuit breakers (SSCB) have attracted much attention in recent years owing to the rise of a new dc application field such as dc microgrids based on distributed generation systems. However, due to the inherent large on-state resistance of power semiconductor devices, the proliferation of SSCB is impeded by a large energy loss and finite fault current interruption capability. Compared with commonly used power devices, metal-oxide-semiconductor (MOS)-controlled thyristor (MCT) features an ultralow on-state resistance high surge current capability, which could be a potential candidate for SSCB applications. In this paper, an evaluation of cathode-short MCT (CS-MCT) in a 400 V dc SSCB is presented by using both physical-based mixed-mode simulation and experimental measurements. Corresponding results show the SSCB based on CS-MCT attains a 30% reduction in energy loss compared with that using insulated gate bipolar transistor (IGBT) and the fault current interruption capability of SSCB can be enhanced by suppressing the mistriggering of CS-MCT. The excellent device performances coupled with inherent reliability of solid-state power switch make CS-MCT a good candidate for future dc SSCB applications. [ABSTRACT FROM AUTHOR]

The application of cascaded multilevel converters in large-scale photovoltaic plants connected to the utility grid has many advantages, such as the absence of sinusoidal filters and line-frequency transformers. Improved overall performance under partial shading conditions is possible due to the distribution of arrays among a large number of maximum power point trackers. In this situation, although the cells operate at different power levels, the three-phase currents injected into the point of common coupling must be balanced. A suitable control technique is required to achieve this goal. This paper presents a complete algorithm to handle three-phase power balance and single-phase power harvesting simultaneously. Simulation results assuming a medium-voltage system connected to a typical utility grid illustrate the dynamic and steady-state performance capability of the proposed strategy. Experimental results of a low-voltage, solid-state transformer-based, three-cell prototype are also included. [ABSTRACT FROM AUTHOR]

Current commutation from the load current path to the commutation path is the precondition to interrupt current successfully for hybrid direct current circuit breakers (DCCB). With remarkable current commutation performance, current commutation drive circuit (CCDC), mainly consisting of air-core transformer, fast-closing switch (FCS), and precharged capacitor, is proposed by us. In this paper, to eliminate the operating losses of CCDC and to avoid unrecoverable damage of FCS, CCDC used in hybrid DCCB for current commutation has been improved. Different submodules (SM) of commutation path in hybrid DCCB are analyzed, and experiments have been carried out on a hybrid DCCB prototype. Theoretical analysis and experiment results have shown that no matter which kind of SM is used, improved CCDC can ensure reliable current commutation in hybrid DCCB. In the end, by taking total cost of CCDC into consideration, a novel optimization method is proposed to design the parameters of CCDC. With this optimization method, CCDC for hybrid DCCBs with different rated voltage and current can be designed individually and its cost could be reduced significantly. [ABSTRACT FROM AUTHOR]

Current control of a switched reluctance motor (SRM) is challenging due to nonlinearity and double saliency of the machine. A linear proportional-integral (PI)-based current controller, which is popular in other electrical machines, cannot be directly applied, as this requires a linearized machine model. This paper examines different small-signal linearized models for an SRM and identifies the model best suited for the purpose of current controller design. This paper then utilizes this linearized model to propose a fixed proportional-integral (PI)-based current controller, the parameters of which can be selected directly from the machine parameters. This paper also proposes a simple method to evaluate back-electromotive force (EMF) for the purpose of disturbance rejection during current control. The performance of the proposed fixed-PI-based control with back-EMF compensation is better than that of delta modulation in terms of current ripple; it is comparable to that of variable-gain PI with back-EMF compensation in terms of current ripple and current reference tracking. While variable-gain PI requires knowledge of the entire flux-linkage characteristics and involves calculation of controller gains in every sampling interval, the proposed method requires only limited details of the motor characteristics and is much simpler to implement. [ABSTRACT FROM PUBLISHER]

In this paper, a new technique to equalize light-emitting diode (LED) currents in multiarray LED lamps is proposed. The current through the LEDs is controlled by changing the inductance of a variable inductor. The proposed technique can be employed to control the current through each LED branch independently. The operation principle of this technique and a design example of the proposed system are presented in detail in this paper. As an example, a forward converter has been selected to supply the LED branches, which can be designed to operate with one or several outputs. The component values of the converter as well as the LED current control circuit are also calculated as a design example. A prototype of the circuit has been implemented. The experimental results obtained at the laboratory are satisfactory and in accordance to the proposed design methodology. The proposed technique can prove to be very cost-effective for LED drivers in the range of 100 W and beyond with multiple independent LED arrays. [ABSTRACT FROM AUTHOR]

This paper presents a literature review on magnetically-controlled devices, variable inductors (VI), and variable transformers (VT), and their applications to lighting gears for discharge lamps and/or LED lamps. These current-controlled devices are mainly characterized by nonlinear and non-uniform saturation of the magnetic core. The paper describes the fundamentals and basic operating principle of such devices and provides an overview of existing patents. These patents refer the devices, VIs or VTs, as useful or industrially applicable. Some present one or more claims regarding the construction of the device and behavioral characteristic; others refer to specific applications, such as voltage regulation or universal ballast operation. Afterwards, the paper focuses on the review of specific techniques and circuits taking advantage of the presence of a controlled inductance value, by covering recent applications regarding discharge and solid-state lamp drivers. These applications will show how these multi-winding devices, typically not considered due to their low efficiency, may fulfill an important role and add features to state-of-the-art lamp drivers. [ABSTRACT FROM AUTHOR]

The benefits of variable-frequency drives (VFDs) have not been fully realized in many applications because they compete in the power density of legacy equipment, such as electromechanical motor controllers. This is particularly the case in Navy shipboard systems where sensitive equipment is in close proximity to VFDs. This paper compares the power densities, efficiency, and costs of both voltage-source- and current-source-based VFDs. A meaningful comparison is made based on actual hardware implementations that meet stringent power quality and electromagnetic compatibility requirements. The hardware results of a current-source-rectifier (CSR)-fed voltage-source inverter (VSI), or a CSR–VSI-based VFD, are provided in order to support the findings of this paper. Special consideration is given to operation at light loads. [ABSTRACT FROM AUTHOR]

The energization of power transformers is a frequent operation in electric arc furnaces (EAFs). Magnetization inrush currents with 10–50 times the rated transformer current can flow during several line cycles. The magnitude of the inrush currents depends on parameters like the point on wave of voltage energization, residual flux in the core, transformer size, and utility systems characteristics. This momentary high current results in system disturbances and reduction of the transformer life cycle. In this paper a scheme to mitigate large inrush currents using controlled voltage ramp soft-starter-based circuit is presented. Simulation and experimental results prove the effectiveness of the soft-starter-based controlled energization. [ABSTRACT FROM AUTHOR]

Paralleled inverters are not only a suitable approach to increase the power capacity, but also have the capability of common mode voltage (CMV) reduction, or even elimination. The original zero CMV modulation scheme for paralleled inverters suffers from the current jump problem in phase-leg currents. This current jump phenomenon amplifies the peak values of differential-mode circulating current (DMCC) and zero-sequence circulating current (ZSCC), which is adverse for the design of coupled inductor and common-mode inductor. This paper introduces the modified modulation scheme, which can keep volt-seconds balance in whole fundamental period and mitigate the current jump in phase-leg currents. In addition, the reduction effect of the DMCC and ZSCC can be achieved. To verify the analysis, both the simulation and experimental results are presented, which validates the proposed methods and show that they are beneficial for DMCC and ZSCC reduction. [ABSTRACT FROM AUTHOR]

Motor current signature analysis (MCSA) provides a nondestructive and remote approach for a gear fault diagnosis. However, in addition to the fault-related components, motor current in the faulty gear system also contains the eccentricity-related components and gear meshing-related components, which contaminate the fault features and increase the difficulty of fault diagnosis. To extract fault features from these interferences, this paper proposes the dual parameters optimized resonance-based sparse signal decomposition (RSSD) method, which can decompose a complex signal into a high- and low-resonance component with two sets of overcomplete wavelet bases. After the decomposition, the fault-related components, which have short duration, will exist in low-resonance component. The novelty is that the wavelet bases related parameters, Q-factors, and decomposition levels are chosen automatically based on artificial bee colony algorithm to obtain the optimal decomposition results instead of chosen subjectively. Kurtosis of the low-resonance component is employed as optimization index. The proposed method is then verified on the gear fault-diagnosis platform, which consists of two permanent magnet synchronous motors and a pair of gears with transmission ratio of 3:2, and its effectiveness over some existing methods under different operating conditions is also validated. [ABSTRACT FROM AUTHOR]

Harmonics have been considered as one of the major issues in future power grids. With the increasing demand in advanced control functions, power electronic converter interfaced distributed generators (DGs) are expected to perform harmonic compensation when necessary. It has been demonstrated in a number of studies that DG converters operating in voltage-controlled mode can be easily configured to realize voltage harmonic compensation utilizing naturally embedded voltage control loop. While for DGs operating in current-controlled mode (CCM), such function was rarely studied. Considering that CCM is commonly used in renewable energy based generators and energy storage systems, it has certain significance to achieve the same function with CCM converters. Aiming at such objectives, this paper proposes a voltage detection based harmonic compensator (HC) for CCM converters. The novelty and main advantages of the proposed method include the following. It realizes seamless interface of HC with inner fundamental current control loop. Compared with a conventional active power filtering method, it does not require remote load harmonic current measurement since it is local voltage detection based. Compared with a conventional voltage detection based method, it offers better performance because of directly harmonic voltage regulation. Experimental results are presented to demonstrate the effectiveness of the method. [ABSTRACT FROM PUBLISHER]

The ever growing penetration of distributed generation (DG) in a distribution network has a profound impact on network protection and stability. Traditional protection schemes and algorithms need to be extensively investigated as more and more DGs get introduced into the network. The current version of IEEE Standard 1547 does not present a comprehensive solution for fault current detection in the presence of various kinds of DGs. Power electronic inverter-based DGs (IBDGs) are of special concern in distribution network protection as they are often incapable of providing sufficient fault current and their controllers play a principal role in the DG behavior. In this paper, the effects of voltage and current controllers for IBDGs on industrial and commercial power system protection schemes are investigated. It is shown that the inverter control mode has a direct impact on its fault current levels and duration. A simplified distribution network model with IBDG operating under voltage and current control modes was tested to verify the effects of these controllers. This paper also proposes an adaptive relaying algorithm to detect the faults in the presence of IBDGs with various types of controllers. [ABSTRACT FROM AUTHOR]

This paper proposes a novel multifunctional controller for a dimmable high-power-factor single-switch electronic ballast that can be used with standard phase-cut dimmers. Conventional dimmable electronic ballasts lack the ability to 1) provide smooth dimming and maintain high power factor when phase-cut dimmers are used and 2) regulate the lamp power when the input line voltage varies. A digital controller with multiple control functions is proposed in this paper. The proposed controller allows high power factor to be achieved by controlling the duty cycle during dimming with standard phase-cut dimmers. On the other hand, when dimming is not required, the lamp power is regulated through the regulation of the dc-link voltage. Additional control functions, such as lamp low-power cutoff operation, and protection function are also implemented inside the digital controller. The descriptions of the controller operating principles and its logic flow diagrams are provided in this paper. PSIM simulation and experimental results are provided on a 13-W compact fluorescent lamp to highlight the merits of the proposed work. [ABSTRACT FROM AUTHOR]

The integration of distributed generation (DG) or distributed resources in the distribution system poses technical constraints for the electrical power system owner or manager. The addition of relatively large amounts of generation to the distribution system can potentially challenge the historical setting principles and design assumptions made in developing protection and control strategies based on overcurrent protection. The necessity and complexity of additional protection and control measures increase as the aggregate DG capacity within a potential island approaches or offsets the load within that island. In addition, the varying nature of DG availability and fault current capability must also be considered. The key issues discussed and associated with DG on the distribution feeder include anti-islanding, temporary overvoltages during fault conditions, and loss of sensitivity of feeder overcurrent protection for long feeders. As the distribution system evolves to accommodate more DG, the design and implementation of the feeder protection must also evolve. This paper presents the use of distance relays for distribution protection to solve some of the DG integration problems. This paper provides real-world event report data to further demonstrate the performance of distance protection on the distribution system. A relative cost comparison between various feeder protection solutions is presented along with a discussion on options for education of distribution companies challenged with implementing distance protection for the first time. [ABSTRACT FROM PUBLISHER]

Zero-sequence circulating current (ZSCC) has been a major concern for the operation of paralleled converters. Existing ZSCC reduction methods in the literature either suffer poor performances or are too complicated for modular implementation in an arbitrary number of interleaved converters. This paper investigates the application of interleaved carrier phase-shift (ICPS) pulse-width modulation (PWM) in modular interleaved converter system for ZSCC peak value reduction. The generalized study based on the derived ZSCC analytical expression reveals that the ICPS PWM can achieve superior ZSCC peak value reduction performance regardless the number of interleaved converters. Moreover, the impacts of ICPS PWM on the output voltage and current quality are also analyzed based on double Fourier integral. Compared with the conventional interleaved sinusoidal PWM (ISPWM), the output quality with the ICPS PWM can be comparable or even better. Simulation and experimental results show good agreement with the theoretical analysis, verifying the performance of the ICPS PWM. [ABSTRACT FROM AUTHOR]

Recent developments in smart metering applications have led to the conceptualization and construction of a new type of energy meter, operating on the basis of event-driven principles. The event-driven metering concepts are applied to represent the information on the electrical load patterns, which have an integral value. This paper explains why these concepts are different from the ones used for event-based applications in other domains, discusses the principles used in the new type of electricity meter, presents the data formats structured in such a way to provide detailed knowledge representation, and shows a number of results on real-case applications. A specific index is defined in order to represent the effectiveness of the event-driven metering scheme illustrated to represent the details of the metered pattern, comparing the results with the ones that could be reached in the most favorable case through regular timer-driven metering. The presentation of specific applications based on real-life datasets highlights the advantages of the event-driven energy metering over the traditional timer-driven metering scheme. [ABSTRACT FROM AUTHOR]