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This paper describes a flow control of the dye in the paper mill with the quasi-Z-source indirect matrix converter (QZSIMC) fed induction motor drive. More than a decade the voltage-source inverter (VSI) and current-source inverter (CSI) have been used to control the speed of the induction motor, which in turns controls the flow of dye. Recently, the matrix converter (MC) has been an excellent competitor for the VSI or CSI for its compactness. The voltage transfer ratio of the VSI, CSI, and MC has been limited to 0.866. Thus, the efficiency of these converters is less. To improve the voltage transfer ratio the quasi-Z-source network (QZSN) is to be used between voltage source and indirect MC (IMC). The modification in the shoot-through duty ratio of the QZSN varies the voltage transfer ratio greater than 0.866. Different voltage transfer ratios are needed for different voltage sag conditions. For a variation of the duty ratio of the QZSN, the fuzzy logic controller has been presented. To control the IMC vector control with space vector modulation has been presented. This paper proposes the implementation of QZSIMC adjustable speed drive for the flow control of dye in paper mill during different voltage sag conditions. A 4-kW prototype has been built and the effectiveness of the proposed system is verified with simulation results and experimental setup. Simulation is done in MATLAB, Simulink platform. Experimental setup is done with the aid of a TMS320F2812 (Texas Instrument) processor. The experimental results validate the maintenance of the speed of an induction motor at the set condition, thus controlling the perfect flow of dye in paper manufacturing technology. [ABSTRACT FROM AUTHOR]

Voltage rise caused by high levels of distributed generation is manifesting as voltage regulation challenges for many electricity network service providers. In this environment it would be ideal to reduce supply voltage magnitudes, however, many network operators are hesitant to do so due to concerns related to consumer appliance performance at reduced supply voltage magnitudes. Voltage regulation requirements are defined by network standards and network service providers must ensure voltages remain within specified limits. Through an evaluation of domestic appliance performance when supplied at various voltage magnitudes, this paper examines the impact of varying voltage levels on residential appliances. Equipment energy demand, operation and actuation were monitored for each applied voltage magnitude. While no equipment failures were recorded, appliance behaviour varied significantly with applied voltage magnitude. Individual appliance conservation voltage reduction (CVR) factors have also been established. The results highlight the importance of good voltage regulation and provide substantiated appliance performance figures for future studies. The outcomes of this paper allow electricity network service providers to understand the implications of supply voltage magnitude on domestic appliance performance, whether it be understating of the impact of higher voltage magnitudes caused by distributed generation or implications of reducing voltage magnitudes to provide headroom for distributed generation integration. [ABSTRACT FROM AUTHOR]

Standard TRIAC-based dimmers introduce power quality issues especially for a large-scale lighting network. Other existing dimming protocols involve additional wiring systems and/or additional controllers to light emitting diode (LED) drivers. This paper proposes a central dimming system for a large penetration of LED lamps. The dimming system is remotely controlled through a webpage or a desktop application. Dimming is achieved while maintaining high voltage and current quality waveforms, which results in a high power factor and a low input current harmonic distortion. The system does not require additional wiring or specific adjustments to commercial dimmable LED drivers. The system allows scheduling a dimming profile to endorse energy saving. In the proposed dimming system, dimming function is achieved by connecting a voltage source converter (VSC) between the grid and the LED lamps. An advanced feature is added to the VSC dimmer to remotely send/receive messages between the system and the user through a graphical user interface. Thus, the user can communicate with the VSC dimmer by sending commands and receiving feedback information. The influence of communication delay on system stability is analyzed by using small signal models. A VSC dimmer prototype (500 VA/120 V) has been built with a communication module to provide remote control. Experimental results and comparisons between utilizing the TRIAC-based dimmer and the VSC dimmer for dimming function are discussed in the paper. [ABSTRACT FROM AUTHOR]

The development of the dc microgrid system on-board has promoted the development of the dc circuit breaker, but short circuit fault may cause serious damage to the system. Many problems exist in the traditional dc circuit breaker such as long periods of fault interruption, complex circuit structure, existing arc, low reliability, and low anti-interference. Aiming to solve these problems, a novel solid-state dc circuit breaker is proposed in this paper. First, this paper analyzes the working principle and process of the circuit in detail according to the results of the simulation based on Saber. Second, this paper gives the criteria on how to choose the parameters of the components correctly in the circuit. The concept of the maximum fault resistance according to the minimum fault current is also introduced. Moreover, this paper analyzes the influence of the minimum fault ramp rate on the circuit performance. Finally, experimental results verify that the performance of this novel solid-state circuit breaker agree with the theoretical analysis. [ABSTRACT FROM AUTHOR]

Voltage and current waveforms contain the most authentic and granular information on the behaviors of power systems. In recent years, it has become possible to synchronize waveform data measured from different locations. Thus large-scale coordinated analyses of multiple waveforms over a wide area are within our reach. This development could unleash a set of new concepts, strategies, and tools for monitoring, protecting, and controlling power systems and apparatuses. This paper presents an in-depth review and analysis of the advancements in synchronized waveform data, including measurement devices, data characteristics, use cases, and comparisons with synchrophasor data. Based on the findings, five strategies are proposed to discover and develop synchronized waveform based applications over multiple application areas. The paper also presents three complementary measurement platforms and two data screening algorithms for application implementation. It further discusses committee activities and standard developments useful to explore the full potential of the data. [ABSTRACT FROM AUTHOR]

The inrush current generated by power transformer energization (TE) causes voltage sag of the nearby bus, the typical residual voltage of the voltage sag caused by transformer energization (VSTE) is about 0.7 p.u.--0.9 p.u. and lasts for a longer duration, which may lead to the sensitive equipment trips. This paper proposes an estimation method of voltage sag frequency considering VSTE. Firstly, based on the maximum entropy method, the residual flux distribution is calculated by considering the relationship between the residual flux and closing angle at the moment of TE. The voltage sag waveform caused by TE is calculated based on the estimation of the probability distribution of residual flux, to evaluate VSTE objectively and comprehensively. Secondly, this paper proposes a non-rectangular voltage sag equivalent frequency statistical method based on multiple magnitude-duration (MMD) function, to avoid the overestimation of voltage sag frequency by the traditional methods. Furthermore, this paper proposes an assessment algorithm of voltage sag frequency. Finally, the simulation of IEEE-30 test system verifies the necessity and correctness of the proposed method. [ABSTRACT FROM AUTHOR]

Modern electric grid usages extensive non-linear loads leading to the increased harmonic current injection in the system. This paper proposes a data-driven algorithm based on a sparse decomposition approach with the Overcomplete Hybrid Dictionary (OHD) and provides in-depth mathematical analysis to detect and mitigate harmonics in emerging electric power systems. The sparse decomposition method is widely used in image processing applications with significant advantages to big-data applications. However, its application is not properly addressed in electric grids’ applications despite massive data generation in a smart grid environment. Hence, in this paper, the performance evaluation of a sparse decomposition-based algorithm using a greedy approach is proposed and carried out in a real-time simulation environment for Distribution Static Compensator (DSTATCOM) application for the real-time detection, classification, and mitigation of PQ events to show its suitability and effectiveness. Finally, the experimental results on a small-scale laboratory setup are presented to validate the effectiveness of the proposed sparse-based control algorithm for DSTATCOM in real-time applications. The comparative result shows that the proposed sparse-based method is advantageous for off-line PQ signal processing and capable of real-time detection, classification, and control of the power apparatus for harmonics mitigation. [ABSTRACT FROM AUTHOR]

Point-on-wave (POW) is a single-event characteristic of voltage dips, influencing the performance of sensitive equipment, such as AC contactor and wind turbines. However, definition and calculation of POW are unsolved issues. The existing definition of POW is for single-phase dips; it does not consider three-phase dips. Moreover, existing POW calculation methods are inaccurate. This paper proposes a definition of POW as a single-event characteristic for three-phase voltage dips. Then, it proposes a POW calculation method based on space vector, including POW detection and angle calculation. The proposed method is based on the ellipse characteristics during the dip-stage and non-dip stage. The proposed method does not depend on zero crossing for angle reference. To verify the performance of the proposed method, a power-system simulation model is built to generate voltage dips with different origin. Furthermore, the accuracy of the proposed method is verified by 425 sets measured voltage dips, and compared with the published methods. [ABSTRACT FROM AUTHOR]

The main standard for avionic equipment DO-160G defines a set of tests that require compliance before the employment of a device in aircraft. An important test involves the generator voltage and consequential current distortion of the three-phase load in the variable 360–800 Hz frequency grid. The main purpose of this paper is to present and analyze a systematic design methodology for three-phase boost and buck rectifiers in order to meet with the voltage distortion test requirement. For a given voltage harmonic profile, the current harmonic limits that have to be satisfied are translated into equivalent per-harmonic admittances and a profile of maximum rectifier input admittance versus frequency is obtained. The defined profile, due to normalization, is applicable to arbitrary power level with simple shifting by the base admittance governed by the converter nominal power. It is shown that for boost-type rectifiers there is a tradeoff between current controller bandwidth and input inductor size, while for the buck-type rectifiers main limitation lies in the input LC filter design used for differential electromagnetic interference filtering. The experimental results conducted on an SiC three-phase 10 kW VIENNA rectifier are tightly backing up the proposed theoretical analysis. This paper is accompanied by three videos demonstrating experimental measurement of d-axis open-loop duty cycle to inductor current transfer function, loop-gain of d-axis current controller with 3.8 kHz bandwidth and variable grid frequency 360–800 Hz operation of the converter under 0% and 10% input three-phase voltage total harmonic distortion. [ABSTRACT FROM AUTHOR]

Transformations between abc, stationary dq0 ($\alpha \beta 0$) and rotating dq0 reference-frames are used extensively in the analysis and control of three-phase technologies such as machines and inverters. Previous work on deriving the matrices describing these transformations follows one of two approaches. The first approach derives Clarke's matrix by modifying symmetrical components. Park's matrix can be subsequently found from a rotation matrix. The second approach derives Park's matrix using trigonometric projection by interpreting the transformation as a rotation in the plane of the cross-section of a machine. Then, Clarke's matrix can be found trivially using a reference angle of zero in Park's matrix. This paper presents a third approach to deriving the Clarke and Park transformation matrices: a geometric interpretation. The approach exploits properties of the linear transformation using the Cartesian representation. We introduce the locus diagram of a three-phase quantity and show how these diagrams have applications in power quality. We show that, unlike a phasor diagram, a single locus diagram can fully represent a three-phase system with harmonics. [ABSTRACT FROM AUTHOR]

As high-speed railways develop rapidly worldwide, the problems of neutral section and power quality are becoming increasingly prominent. These problems affect the normal operation of the power grid and the electric locomotives. The co-phase power supply schemes were proposed by researchers, which can solve these problems well. Among them, the MMC-based scheme (MMC-5 L) is a representative one. The existing scheme, when applied to the auto-transformer (AT)-fed system which is usually adopted by high-speed railways, needs to install an auto-transformer on the output side. To eliminate the auto-transformer and to obtain the more suitable and superior co-phase power supply schemes to AT-fed system, two improved schemes are proposed in this paper based on the novel MMC-based scheme (MMC-6 L) we proposed before. While establishing the mathematical model, creating the control system, and carrying out simulation verification of the proposed schemes, the proposed schemes are compared with MMC-6 L and MMC-5 L in terms of topological characteristics, control system complexity, power loss, and functionality. The results show that while the proposed schemes can fulfill the functions of the co-phase power supply scheme well like the MMC-5 L and MMC-6 L, they are more suitable and superior for the AT-fed system in terms of control system complexity and power loss. Among them, MMC-5L1CB performs best in power loss, and MMC-4L2CB performs best in control system complexity. [ABSTRACT FROM AUTHOR]

Power sharing amongst sources can be improved in an islanded microgrid by utilizing the information of the network’s impedance. In this paper, an impedance based model reference adaptive system (Z-MRAS) scheme is proposed to estimate the impedance angle for converter based distributed generators (DGs) in the islanded mode. The focus is to enhance the proportional apparent power sharing between the DGs operated using generalized droop control (GDC). The performance of GDC depends on the effective tie-line impedance between the DGs and the proposed MRAS scheme provides the feedback of the estimated impedance angle. The accuracy of the impedance angle estimation is established for various tie-line $X/R$ ratios, and this results in enhanced power sharing performance for balanced, harmonic, unbalanced, dynamic and constant power load cases as well as parallel line and underground cable cases. The proposed method is validated through off-line simulations in MATLAB and controller hardware in loop (CHIL) using real time simulator (Opal-RT) including cases of meshed networks and DG plug and play for a modified CIGRE network. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamic voltage support (DVS) from inverter-based resources (IBRs) under voltage sags to enhance the low-voltage ride-through performance. The DVS problem is formulated as a nonconvex optimization program that maximizes the positive-sequence voltage magnitude at the point of common coupling (PCC) subject to the current, active power, and synchronization stability constraints. Then, we perform the optimality analysis to explore the global optimum analytically. It is found that the unique global optimum has three scenarios/stages (S1–S3), which depends on the specific relationship among grid voltage, grid strength, and physical limits of IBRs. The explicit closed-form solutions in S1 and S3 are derived, and the optimality conditions (an implicit solution) of S2 are provided, which guarantees the global optimality and enables the compatibility with fast real-time control. Finally, we implement the optimum with a grid-connected single-stage photovoltaic (PV) power plant by integrating a DVS controller. Dynamic simulations are carried out under different scenarios to test our proposal. The robustness against model errors is also discussed. [ABSTRACT FROM AUTHOR]

This paper presents a new stochastic approach to the comprehensive assessment of the impact of voltage sags on large-scale power networks. The approach takes into account the stochastic nature of power system operation, including load variation, uncertainty of fault clearing time by protection relays, fault rates of network components, and the variation/uncertainty in equipment sensitivity to voltage sags. A new duration zone division method is used to derive sag duration and occurrence frequency based on the stochastic distribution of clearing time required by specific protection systems. The adopted probabilistic representation facilitates estimation of network performance based on a single-event characteristic, sag severity index (SSI), developed in the companion paper (Part I). Based on SSI, a new single-site index with respect to voltage sags (bus performance index BPI^S) is developed to comprehensively represent the overall bus performance with respect to voltage sags. The index is used to identify the areas of the network, called weak areas of the network in this paper, containing buses that are most exposed to potentially disruptive voltage sags. The application, robustness, and sensitivity of BPI^S are thoroughly analyzed and discussed in the paper. [ABSTRACT FROM PUBLISHER]

Voltage sag insurance (VSI) is an effective measure to reduce the voltage sag loss and risk for enterprises with insufficient mitigation confidence or economic ability. However, due to the lack of understanding of voltage sag risk (VSR), it is difficult for power utilities to identify the enterprises with VSI demands, and it is also unable to realize differentiated premium according to different enterprises' situations. To solve the above problems, this paper proposes an improved voltage sag premium model based on VSR. Firstly, the VSR factors are analyzed, such as the hazard, the vulnerability, the exposure. The process immune time is introduced to describe the vulnerability. Based on the traditional consideration of only the ability of users to resist voltage sag, the ability of users to recover from voltage sag is further considered. Then, the risk evaluation model of voltage sag is established. The evaluation results can help power utilities to judge whether enterprises have the demand of VSI. Finally, the improved premium model of VSI based on VSR is constructed to ensure the differentiation and rationalization of the premium. The correctness and rationality of this method are proved by ten manufacturing enterprises in China by analyzing the VSR and comparing the premium before and after the improvement. [ABSTRACT FROM AUTHOR]

Line-commutated converters are extensively used as the interface between ac grids and classic HVDC systems. At the inverter side, commutation failure of switches is one of the most common faults that can pose threats to the system operation. Practical and reliable study of such phenomena relies on accurate and efficient converter models for simulations. Recently, a parametric average-value model (PAVM) has been presented for ac–dc rectifiers, which considers the internal faults of the converter. In this paper, the PAVM methodology is extended to the dc–ac inverter systems, including the commutation failure of switches. The proposed PAVM also augments an automatic fault detection technique to determine the faulty switches. Using comprehensive simulation studies, the developed model is verified to accurately predict the commutation failure of switches and reconstruct the waveforms consistent with the detailed switching models of inverters while being computationally more efficient. The proposed PAVM is envisioned to be an efficient and accurate asset for simulation of HVDC systems and inevitable when faults of switches need to be considered. [ABSTRACT FROM AUTHOR]

Supraharmonic (SH) disturbances are generated mainly by power electronics whose usage has increased significantly in the last decades. Consequently, supraharmonics have increased as well. The SH frequency range from 2 kHz to 150 kHz still lacks a normative measurement method. Compatibility levels and emission limits of SH are commonly presented as quasi-peak (QP) detector values for a bandwidth (BW) of 200 Hz measured by CISPR 16 receivers. In this context, this paper proposes an optimized method emulating the CISPR 16 receiver with QP detector for measuring grid disturbance levels. It makes innovative use of PLL (Phase-Locked Loop) units for estimating the highest distortion levels in the SH frequency range of the test signal, and in sequence, the QP detector with the appropriate specifications in the CISPR 16 standard is applied. Different cases of both synthetic and real signals were applied to the proposed method, which showed to be efficient in evaluating SH levels for current and voltage signals. An analysis of maximum permissible distortion levels is performed considering an individual SH distortion. In addition, the proposed method presents a computational cost reduction of approximately 91% in relation to the CISPR 16 method considering a specific case of signal containing SH distortions used for power quality analysis. [ABSTRACT FROM AUTHOR]

Nowadays, nonlinear loads such as load commutated inverter (LCI) drives are being used by industrial sector throughout the world. However, despite the LCI drive uses low-cost thyristors and their corresponding controllers, which have high efficiency and low manufacturing cost, there are concerns regarding the use of LCI drives which are two-fold: (i) they generate harmonics and (ii) they are sensitive to voltage sags occurring at their PCC. In the literature, passive harmonic filters have been suggested to address the former concern and therefore various filter designing techniques have been introduced. However, the need to elaborate a cost-effective filter to address both concerns regarding LCI drive operation has been neglected. Therefore, this paper presents an innovative approach for designing passive filters which can decrease the harmonic distortions generated by LCI drives while ensuring more reliable annual operation of these equipment. Besides, other aspects of passive filter designing, such as eliminating detuning effects, resonance elimination and harmonic loading of capacitors, have been taken into account to provide a general and practical filter designing approach for real industrial applications. In order to evaluate the innovative proposed approach, a passive filter is designed for LCI drive used in an Iranian large copper mine company. [ABSTRACT FROM AUTHOR]

The paper addresses an improved inner current reference calculation to be employed in the control of modular multilevel converters operating during either balanced or unbalanced conditions. The suggested reference calculation is derived based on the AC and DC additive and differential voltage components applied to the upper and lower arms of the converter. In addition, the impacts caused not only by the AC network’s impedances but also by the MMC’s arm impedances are also considered during the derivation of the AC additive current reference expressions. Another issue discussed in this article regards that singular voltage conditions, where the positive-sequence component is equal to the negative one, may occur not only in the AC network but also internally (within the converter’s applied voltages). Several different inner current reference calculation methods are compared and their applicability during the former fault conditions is analyzed. The paper presents a detailed formulation of the inner current reference calculation and applies it to different unbalanced AC grid faults where it is shown that the presented approach can be potentially used to maintain the internal energy of the converter balanced during normal and fault conditions. [ABSTRACT FROM AUTHOR]

Aging of power system assets challenges utilities to maintain reliable service while minimizing their maintenance costs. Although malfunction of devices in the transmission or distribution networks can have catastrophic consequences, their failure is seldom unforeseen. Typically, the device aging occurs gradually over time until its health condition reaches a point of complete breakdown. The overall objective of this paper is to devise a non-invasive, online condition monitoring technique of circuit switchers for shunt capacitor banks. It aims to detect abnormal operation of these devices based on features derived from raw voltage and current waveforms, such that a predictive maintenance strategy may be employed before a complete failure occurs. The data analyzed in this paper are collected at a transmission capacitor bus, where the banks are equipped with pre-insertion impedance. Through a baseline range of values for selected parameters, the proposed technique is able to detect missing pre-insertion impedance during the capacitor energizing and failure of pre-insertion impedance switch out a few cycles after the energizing operation. [ABSTRACT FROM AUTHOR]

Distributed grid and microgrid are becoming increasingly important in power system nowadays. In these grids, reactive compensations and harmonic current suppression are commonly employed to improve power quality. For the doubly fed induction generator (DFIG), high frequency resonance (HFR) will occur when it is connected to parallel compensation grids. When DFIG system is connected to the harmonic grid with parallel compensation, frequency ranges of HFR and harmonics may have intersections. In this paper, some cases for DFIG system with the HFR damping and harmonics suppressor are given to reveal that the coupling between HFR damping control and harmonics suppression control may lead DFIG system into the unstable situation. Furthermore, a frequency detection is necessary for the existed HFR damping control when compensation capacitor changes, which will deteriorate the HFR damping performance due to the additional detection time on HFR frequency. This paper proposes an impedance reshaping control strategy based on a variable frequency resistance and chebyshev filter, the HFR damping control and harmonic current suppression can be achieved simultaneously to improve power quality for DFIG system connected to the harmonic grid with parallel compensation. Theoretical analysis, simulations, and experiments verify availability of the proposed control strategy. [ABSTRACT FROM AUTHOR]

In order to generate high-voltage high-pulsed power, klystron modulators necessarily contain at least one capacitor bank charging structure supplying the energy to be released during the pulse. Conventional charging structures are based on ac/dc front-end units typically based on diode rectifiers combined with power charging structures operated in on/off mode as a second stage, producing prohibitive levels of grid flicker and harmonic contents on the ac grid side while operating at suboptimal power factor. These problems are usually corrected by both costly and spacious external grid compensators. Today, the increased demand on both accelerator peak power and pulselength (translating into higher average power), in conjunction with stricter regulations and standards represent additional challenges also in modulator design. An alternative method for capacitor bank charging, in a steady state allowing for the complete reduction of grid flicker as well as ac line current harmonics and reactive power, was presented by the authors in a preceding publication. This paper presents in further detail the benefits of the proposed power electronic structure and associated control scheme in the context of a review of other solutions suggested for constant power charging and flicker mitigation. This paper also contains a complete description of the proposed control scheme as well as further experimental results, including a thorough assessment of its performance under transient conditions. All experimental results were obtained on a klystron modulator prototype rated for long pulses (3.5 ms), high voltage (115 kV), and high pulsed power (peak power > 2 MW). [ABSTRACT FROM AUTHOR]

This paper presents an algorithm for detection, classification, and characterization of voltage sags and swells in electricity networks using three-phase voltage ellipse parameters. The proposed method employs the instantaneous magnitude of three-phase voltage signals in three axes, which are separated from each other by 120 ^\circ . Thus, the resultant rotating vector, namely, the three-phase voltage vector, traces an ellipse. Then, the parameters of the ellipse, which include minor axis, major axis, and inclination angle, are used to develop the proposed algorithm for classification and characterization of voltage sags and swells. The proposed method is validated using real data of the IEEE working group and some measured real data of the Belgian transmission grid. The method is further tested for the sags and swells generated due to balanced and unbalanced faults at different buses, in test distribution networks (radial and mesh type) embedded with distributed generation and in a practical distribution network of Australia. This paper also demonstrates the proposed algorithm as a real-time sag/swell monitoring tool. [ABSTRACT FROM PUBLISHER]

Harmonic loads and unbalanced loading in a distribution transformer lead to higher losses, an increase in temperature that leads to premature failure, and a shorter lifetime. To prevent these difficulties, the rated power of a transformer supplying nonlinear loads or unbalanced load is reduced; commonly known as derating. In this paper, an alternative to traditional loss based derating is proposed. It is shown that derating might actually not be required when contrasted with the traditional approach. A perspective is presented on how to make the kVA rating “adaptive” and utilize the same kVA rating with or without harmonics. Actual field data are presented to support this viewpoint. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of switch-mode power supplies used in desktop PCs (PC-SMPS’) across the entire range of operating powers. Experimental results show that at low to medium operating powers, the input ac current might lose its periodicity with supply voltage frequency, when PCS-MPS’ can be an unexpected source of interharmonics and dc component. In such cases, there is a significant increase of PC-SMPS’ current waveform distortion and a substantial decrease of efficiency and operational power factors, which requires application of appropriate measurement and calculation procedures during the analysis. To correctly assess these power-dependent changes in performance and power quality indicators, this paper introduces a novel testing and evaluation methodology, based on the known or assumed PC-SMPS operating cycle. [ABSTRACT FROM AUTHOR]

This paper presents theoretical and experimental discussions on low-voltage-ride-through operation of a modular multilevel single-delta bridge-cell (SDBC) inverter intended for utility-scale photovoltaic (PV) systems. Modern grid codes require grid-tied inverters to provide dynamic grid support during grid-fault events by injecting reactive current. This paper discusses decoupled positive- and negative-sequence reactive-current control, focusing on asymmetric voltage sags with imbalanced magnitude and phase relationships. The main objective is to present a feedforward control method based on calculation of the zero-sequence current required for achieving power balance during normal and grid-fault conditions. Moreover, this paper demonstrates a practical method that minimizes overcurrent stress in the three inverter clusters by adjusting active power drawn from PV arrays. Experimental results on a three-phase 12.6-kVA system prove that the SDBC inverter is capable of seamlessly operating through asymmetric voltage sags. [ABSTRACT FROM AUTHOR]

Inrush currents in transformers can have very disruptive effects, such as voltage sags, false tripping of the protective devices, and mechanical stresses in the transformer windings. This paper shows that there are operating situations that may cause a transformer to draw abnormally high inrush currents. Examples include the normal operation of offline uninterruptible power-supply (UPS) systems, interruptions, voltage sags, and notching. These conditions may produce inrush-like currents of more than twice the value of the “normal” maximum inrush caused by energizing at voltage zero-crossing. For this condition, the term “phase-hop” is used in this paper. Laboratory experiments were performed on four different transformers (1 kVA) with varied characteristics and show the impact of phase-hop in the magnitude of inrush currents. The experiments are also used to validate the Electromagnetic Transients Program model used for the analysis of multiple cases. In addition, the behavior of the magnetic flux in a transformer under phase-hop is investigated and compared with different operating conditions using finite elements. The results of this paper have implications in transformer design and in the operation and design of UPS systems to prevent the damaging effects of phase-hop. [ABSTRACT FROM AUTHOR]

The delta-connected cascaded H-bridge converter has been applied to compensate flicker and unbalance load to meet power quality requirement. Based on the detailed power analysis, this paper presents a dc capacitor voltage-balancing technique for the converter. This paper also proposes a current limit control technique to avoid overstressing the power semiconductor devices of the converter. The control techniques in this paper are verified in a 220-V, 1-kVA laboratory test bench. [ABSTRACT FROM PUBLISHER]

Transmission system operators (TSO) should be able to assess power quality levels in a network in order to properly address the mitigation of power quality problems. High flicker levels might be a serious power-quality problem in transmission networks and are usually caused by arc-furnace operation. TSO can assess flicker levels in real time only at nodes where power-quality measurements are available. As for the rest of the system, a TSO could calculate flicker levels, if a reliable and relatively simple method is available. Besides, proper summation of flicker levels originating from several flicker sources remains an issue to tackle. The paper proposes a simple method for the calculation of flicker levels at all nodes of a transmission network based on the known flicker values at multiple flicker-sources and based on the known network topology. Different flicker summation coefficients are compared and the one that gives the smallest error is chosen. The proposed method enables a TSO to continuously assess flicker levels at all network nodes and to investigate the consequences of network changes on flicker levels. The method was verified on the Slovenian transmission network where the results of flicker calculation were compared with available flicker measurements. [ABSTRACT FROM PUBLISHER]

This paper presents a new method for studying electromechanical transients in power systems using three phase, combined transmission and distribution models (hybrid models). The methodology models individual phases of an electric network and associated unbalance in load and generation. Therefore, the impacts of load unbalance, single phase distributed generation and line impedance unbalance on electromechanical transients can be studied without using electromagnetic transient simulation (EMTP) programs. The implementation of this methodology in software is called the Three Phase Dynamics Analyzer (TPDA). Case studies included in the paper demonstrate the accuracy of TPDA and its ability to simulate electromechanical transients in hybrid models. TPDA has the potential for providing electric utilities and power system planners with more accurate assessment of system stability than traditional dynamic simulation software that assume balanced network topology. [ABSTRACT FROM PUBLISHER]

This paper reports a practical challenge in Distributed Energy Resources (DER) operation: open phase detection. The paper presents a wide variety of naturally occurred open phase events recorded by power quality meters in DER commercial operations. The events demonstrate the complexity of open phase detection due to electrical and magnetic interphase couplings through transformer winding and core configurations. The coupling effect could recreate the missing phase in various patterns so that the DER control and protection systems or control room operators may not detect the anomaly for prolonged period of time. This paper shares experiences of timely DER open phase detection by using power quality data and suggests practical detection guidelines based on waveform signature analytics. The original field records provide credible benchmarking references for algorithm development to meet the new DER open phase detection requirement in the IEEE Stdandard 1547–2018 revision. [ABSTRACT FROM AUTHOR]

The use of power converters is very important in maximizing the power transfer from renewable energy sources such as wind, solar, or even a hydrogen-based fuel cell to the utility grid. An LCL filter is often used to interconnect an inverter to the utility grid in order to filter the harmonics produced by the inverter. Although there is an extensive amount of literature available describing LCL filters, there has been a gap in providing a systematic design methodology. Furthermore, there has been a lack of a state-space mathematical modeling approach that considers practical cases of delta- and wye-connected capacitors showing their effects on possible grounding alternatives. This paper describes a design methodology of an LCL filter for grid-interconnected inverters along with a comprehensive study of how to mitigate harmonics. The procedures and techniques described in this paper may be used in small-scale renewable energy conversion systems and may be also retrofitted for medium- and large-scale grid-connected systems. [ABSTRACT FROM PUBLISHER]

Voltage imbalances are one of the most severe challenges in electrical networks, which negatively affect their loads and other connected equipment. This paper proposes a voltage support control strategy to mitigate the voltage imbalance in inverter-based low voltage distribution networks. The control scheme is derived taking in mind the following control objectives: a) to increase the positive sequence voltage as much as possible, b) to decrease the negative sequence voltage as much as possible, c) to inject the power generated by the primary source, and d) to minimize the output current of the inverter. The innovative contribution of the proposed solution is based on the design of a control algorithm that meets the aforementioned objectives without resorting to communications with other grid components. The theoretical results are experimentally validated by selected tests on a laboratory setup with X/R ratio close to one. [ABSTRACT FROM AUTHOR]

This paper proposes a new method for measurement-based modeling of nonlinear loads in power systems. The proposed method includes a combination of a binary tree algorithm with nonlinear autoregressive with exogenous input (NARX) identification. This paper demonstrates that the new method performs well without any prior knowledge of the system structure. In contrast to other load modeling methods, which are typically aimed for particular studies or load types, the proposed method can be used with any load type and for any study. Accurate load modeling is particularly important for studies of industrial networks and grids. In the study described, a field data set was collected at a mine site from a large electrical rope shovel. This data set has been used to develop a model of the rope shovel based on the proposed binary tree—NARX algorithm. When compared to other known methods, such as wavelet and sigmoid networks, the proposed method has shown the fastest training time and the highest accuracy. Finally, the modeling results have been verified against another set of field measurements from an existing network and have shown a very good agreement. [ABSTRACT FROM PUBLISHER]

Transient behavior in grounding systems related to electric arc furnaces (EAF) might be studied using an approach to Kron’s circuit model to solve Maxwell’s differential equations in electromagnetic field theory. This paper presents a circuit model designed using Kron’s approach implemented in alternative transient program (ATP). The model is suitable to describe accurately the behavior of real complex grounding systems dealing with continuous operation of an EAF. Some ideas about the behavior of the power quality are evaluated by simulation of the grounding system in ATP. [ABSTRACT FROM AUTHOR]

Reliable operation of multichannel power electronic converters in a large pumped storage power plant (PSPP) is a main concern among policymakers and/or hydropower project developers. This paper aims to design a two-stage protection circuit operation strategy for a large-rated doubly fed induction machine (DFIM) employed for variable-speed PSPPs. This paper initially studies the dynamic behavior of DFIM under symmetrical short-circuit faults in both the 400-kV power system and at stator terminal of the generating unit. Based on the fault analysis, a two-stage protection circuit (dc-link braking chopper circuit and crowbar protection circuit) operation strategy is designed in consideration of practical limitations. The designed operation strategy ensures the continuous operation of large-rated DFIM under marginal grid disturbances. To investigate the effective operation of a two-stage protection circuit, a 250-MW DFIM with multichannel power converters is implemented in MATLAB/Simulink tool. An experimental test is carried in a 2.2-kW DFIM laboratory prototype. [ABSTRACT FROM AUTHOR]

Reduced switch active phase converters (APC) are cost-effective solutions for running three-phase loads from single-phase grids. This paper proposes a novel auxiliary-capacitor-based APC (AC-APC) for this application. The combination of the topological location of the auxiliary capacitor and the control of the AC-APC reduces current stress on the semiconductor devices. In this paper, a selection criterion for the optimal auxiliary capacitor value is formulated to reduce the device currents in such a way that the overall efficiency is enhanced. This paper presents a comparative analysis of converter volt-ampere (VA) rating and device power loss for conventional H-bridge active front-end and inverter-based topology, APC, and AC-APC. To evaluate the efficacy of the proposed AC-APC, an experimental study is conducted on the APC and the AC-APC feeding a 3-hp three-phase induction motor. At a full load of $\text{2.5}\,\text{kW}$ and $\text{0.8 } \text{power factor}$ , the measured maximum efficiency of the AC-APC is $2\%$ higher than that of the APC. Analytical evaluation of converter currents and device power loss are in close agreement with experimental observations. [ABSTRACT FROM AUTHOR]

This paper proposes solutions to the problem of voltage sags caused by distributed generators anti-islanding protection. This is a recently identified power-quality (PQ) concern resulting from the increasing penetration of distributed generators into distribution networks. This problem has been previously investigated by the authors and it was revealed that it can seriously affect PQ indices as well as distributed generators reconnection procedures. However, no solutions have been formerly proposed or investigated. In this context, this paper investigates several potential solutions to be adopted by the utility and/or by the DG owners and presents a thorough evaluation of their main advantages and disadvantages. Besides this investigation, simple step-by-step procedures for assessing the effectiveness of each solution are described. The presented studies and procedures will guide the utility engineers in decision-making process associated with the choice of reasonable mitigation techniques to this problem. [ABSTRACT FROM PUBLISHER]

The international thermonuclear experimental reactor poloidal field converter unit is comprised of four converter bridges, dc reactors, dc switches, etc., and most are nonstandard. To evaluate the performance of these equipments, a high-power dc test platform has been built to carry out the steady-state current test and impulse current test. The latter is significant to verify the fault suppression capability of products. The dc test platform can output the rated 400-kA impulse current. The principle design and structure of the dc test platform is introduced in this paper. The transient large current in impulse current test could cause huge impact reactive power and grid voltage sag. The impact is analyzed by theoretical calculation and simulation. A static var compensator system is added to suppress the transient effects of the reactive power. A predictive reactive power control strategy is proposed to improve the dynamic response. The comparisons with the traditional control demonstrate that the proposed control is effective in compensating impact reactive power and it also performs well on inhibiting the grid voltage sag. [ABSTRACT FROM AUTHOR]

This paper will present a new approach that is advantageous to medium-voltage (MV) distribution design configurations for large industrial and power distribution system configurations [specifically main-tie-main (MTM)] for large industrial and power station installations. Sixty years of traditional low-cost design approaches (typical MTM and operated with open tiebreaker) are re-evaluated to demonstrate that traditional low capital cost design may miss improvement opportunities. Those opportunities can be major capital expenditure reduction, power quality improvement, MV motor soft starter deletion, and improved system stability to name a few. Many designers may not have considered the component interrelationships and/or their tradeoffs when in an integrated system. The designer and/or user should consider the advantages of higher short-circuit capacity (SCC) systems by integrating fault current limiters and MV switchgear. Utilizing higher SCC systems permits power system designer optimization opportunities not possible before using conventional design methods. This paper will provide documentation of substantial savings of capital investment and energy under higher SCC conditions. The savings in one system component will offset another's increased cost. An obvious benefit of stiffer systems is ease of direct-on-line starting of large motor-driven compressor trains. The future need for motor soft starters minimizing system impact will be challenged. This paper may change fundamental system design methodology for system designers by removing several performance tradeoffs. This paper, in its original version, was previously presented at the 2010 IEEE/IAS/Petroleum Chemical Industry Conference. It was expanded with new sections for the 2017 IEEE/Industry Applications Society (IAS)/Pulp, Paper Forestry Industries Conference to include pre-emptive prefault adjustable power quality and multisourced networked power systems. [ABSTRACT FROM PUBLISHER]

The inevitable voltage sag events cause losses to distributed generation (DG) and sensitive users. Reasonable planning for both of them helps to mitigate the impact of voltage sag. In this paper, a joint optimal planning method is proposed for DG and large sensitive user (LSU) considering the influence of voltage sag. Firstly, the new models of accelerated trip and chain trip for DG under voltage sag are established, to characterize the influence of DG tripping on other DG and sag characteristics during the sag event accurately. Secondly, a new voltage sag frequency assessment method is proposed, which considers models of accelerated trip and chain trip for DG, the tripping characteristics of distance protection (DP), to quantify the voltage sag severity accurately of DGs and LSUs in the gird which is with DP. Lastly, a joint optimal planning model is established considering the losses of DG and LSU under voltage sag, to support the planning of DG and LSU in different scenarios. The method is applied to IEEE RTS-30 for verification, proving that the method can give a direction of the most beneficial solution for the planner, to reduce the losses of voltage sag to both the power system and users. [ABSTRACT FROM AUTHOR]

The increased penetration of wind power has made its low voltage ride through (LVRT) capability more crucial than ever. Currently, the LVRT performance of wind generators is verified using experimental voltage sags with different magnitudes and durations. The actual fault, however, also causes the phase angle jump (PAJ) of the grid voltage. In this paper, the impact of PAJ on the LVRT capability of doubly fed inductor generator (DFIG) under three-phase fault is analyzed. To achieve this, detailed analytical calculations and experimental verifications are conducted. The results demonstrate that the PAJ imposes more challenges on the LVRT by intensifying the rotor overcurrent through the natural stator flux. As a result, DFIGs that have passed the existing LVRT test may still fail to comply with the grid code requirements in practice. To tackle this issue, an improved test procedure is recommended. The new procedure considers the impedance angle of the target system as an additional test condition, thus can reveal the LVRT performance of DFIG under the potential PAJ. [ABSTRACT FROM AUTHOR]

One of the consequences of voltage sags is unexpected motor trips or stalls. This is caused by the simple voltage-magnitude-based tripping logic used in the motor contactors. Since a motor has momentum during a voltage sag, a deep voltage sag with a short duration does not necessarily lead to motor misoperation. Based on this reasoning, a novel motor contactor operation scheme is proposed in this paper. The proposed scheme takes into account both the magnitude and duration of a voltage sag plus the momentum of the rotor, in real-time, to decide if a motor will be tripped. The core idea of the scheme is to utilize the critical clearance time (CCT) of motors as the tripping time of AC contactors. The proposed scheme combines an offline analysis and an online calculation to minimize the computation burden in real-time operation. An improved motor parameter estimation method is also proposed to ensure the accuracy of the calculated CCT. The performance of the proposed scheme is evaluated and demonstrated through comparative case studies. Moreover, some practical issues are discussed to facilitate the real implementation. [ABSTRACT FROM AUTHOR]

So far, there is no literature to evaluate the fault level of sensitive equipment (FLSE) caused by voltage sag from the perspective of the power grid. In practice, although the FLSE are dominated by the voltage sag of node, the voltage sag of the node is associated with whole power grid, including the voltage grade and location of the node, the distance between the concerned node and location of fault, and the weather and date at the time of fault, which are all named as voltage sag properties (VSP). In view of this gap, this paper evaluates the FLSE using the long-time monitoring data of VSP of some regional power grid by data mining method based on multidimensional matrix simplification and the improved gray target theory. The data mining process can be divided into three steps: 1) construct a database consisted of VSP and FLSE using long-time monitoring data, 2) mine the association rules between VSP and FLSE by multidimensional matrix simplification, and 3) match some actual scenario with the mined association rules by the improved gray target theory. Performance and effectiveness of the proposed method are verified through the simulation and field case. [ABSTRACT FROM AUTHOR]

This paper provides an overview of hyperloop technologies, including a brief discussion of key components of a hyperloop system that determine the electric power requirements as a function of time. At-scale hyperloop systems do not yet exist, so a model was used to generate a set of load profiles for conceptual hyperloop realizations at four locations in the United States: two systems in California and one each in Colorado and Ohio. In all four cases, the modeled hyperloop load profiles included pulses in both active and reactive power. Grid modeling was performed to estimate the grid impacts and for discussing grid integration challenges. The paper discusses how energy storage systems might be used to eliminate the pulsating load characteristics or significantly reduce it to accommodate current grid planning guidelines. [ABSTRACT FROM AUTHOR]

Still largely untapped, wave energy may represent an important share in the energy mix of many countries in the future. However, the power fluctuations generated by most wave energy devices with little to no storage means, or without suitable control strategies, may cause power quality issues that must be solved before large wave energy farms are allowed to connect to a network. For instance, large power fluctuations may induce an excessive level of flicker in the distribution networks to which they are currently envisaged to be connected. Although storage appears to be a technically feasible solution, the minimum amount of storage required for a wave farm to become grid compliant with respect to typical flicker requirements is still unknown and is therefore investigated. This study constitutes the first part of this paper. Another issue, on which the second part of this paper focuses, concerns the optimal dimensioning of wave farm electrical components, which is traditionally performed assuming steady-state conditions (i.e., a constant current level), and is thus irrelevant in the case of wave farms outputting power fluctuations of significant amplitude. Hence, a second study, the results of which are presented in this paper, focuses on the minimum current rating for which a submarine cable may be safely operated without thermal overloading. Addressing both these issues is essential to the economic viability of a wave farm as the cost of both storage means and electrical components is highly dependent on their rating and may represent a significant percentage of the capital expenditure. [ABSTRACT FROM AUTHOR]

This paper presents measurements of harmonic and interharmonic current (with 5-Hz frequency resolution) in the complex plane. The complex currents are spread around a center point. For interharmonics, this center corresponds to the origin of the complex plane. For integer harmonics, this center is offset from the origin. A goodness-of-fit test reveals that phase angles of most interharmonics are uniformly distributed. A Monte Carlo simulation based on the measurements has been performed to study the aggregation of the emission from individual turbines to the public grid. Low-order integer harmonics show less cancellation compared to high-order harmonics. Interharmonics aggregate close to the square-root rule for uniform phase angles. [ABSTRACT FROM AUTHOR]

This paper deals with a modified technique for the recognition of single stage and multiple power quality (PQ) disturbances. An algorithm based on Stockwell's transform and artificial neural network-based classifier and a rule-based decision tree is proposed in this paper. The analysis and classification of single stage PQ disturbances consisting of both events and variations such as sag, swell, interruption, harmonics, transients, notch, spike, and flicker are presented. Moreover, the proposed algorithm is also applied on multiple PQ disturbances such as harmonics with sag, swell, flicker, and interruption. A database of these PQ disturbances based on IEEE-1159 standard is generated in MATLAB for simulation studies. The proposed algorithm extracts significant features of various PQ disturbances using S-transform, which are used as input to this hybrid classifier for the classification of PQ disturbances. Satisfactory results of effective recognition and classification of PQ disturbances are obtained with the proposed algorithm. Finally, the proposed method is also implemented on real-time PQ events acquired in a laboratory to confirm the validity of this algorithm in practical conditions. [ABSTRACT FROM PUBLISHER]

Direct current (dc) motor drive systems are extensively used in paper, steel, mining, material handling, and other industrial applications due to the high starting torque and easy speed control over a wide range. They could account for 10%–20% load demand in some industrial facilities and thus have significant impact on the overall system dynamics. However, an adequate dynamic model for this type of loads is not available for power system dynamic studies. In this paper, a comprehensive modeling method for dc motor drive systems is proposed considering two scenarios: 1) The drive will trip when subjected to severe voltage sags, and 2) the drive can ride through when experiencing mild voltage sags. The dc drive trip curve and a simple procedure to determine if the drive needs to be included for dynamic studies are proposed for Scenario 1. The dynamic model for dc motor drive systems, which can be readily inserted in the simulation software, is developed and verified through case studies for Scenario 2. [ABSTRACT FROM AUTHOR]