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This article investigates factors affecting the contributions of battery units to fault currents in grid-connected battery storage systems (BSSs). The work in this article is intended to examine the effects of the state-of-charge (SOC) on battery currents that are drawn due to faults. This article also examines the impacts of charger controller actions on the currents drawn from battery units to faults in grid-connected BSSs. The impacts of the SOC and charger controller on battery currents due to faults are examined for the lead-acid, lithium-ion, and nickel–cadmium battery units. Examination results show that the battery currents due to faults are directly dependent on the SOC. Moreover, these results show that actions of charger controller can support the battery terminal voltage, thus preventing the fast reduction of the SOC. The support of the battery terminal voltage helps in limiting the currents drawn from battery units during faults. The effects of the SOC and charger controller are verified using a 1-MW, $3\phi$ grid-connected BSS, which has lead-acid battery units. Several faults have been created during charging and discharging operations, and at different values of SOC. Test results confirm the direct dependence of battery currents (due to faults) on the SOC. In addition, obtained results demonstrate the ability of charger controller to limit the currents drawn from battery units due to faults in different parts of a grid-connected BSS. [ABSTRACT FROM AUTHOR]

This article develops a survivability-based protection for three-phase induction motor drive ($3\phi$ IMDs) systems against severe dynamic events. The developed protection is based on defining a survivability index $\Gamma _{\text{IMD}}$ , which is formulated in terms of the change in power created by a dynamic event experienced by a $3\phi$ IMD. The determination of $\Gamma _{\text{IMD}}$ provides an accurate tool to detect, identify, and respond to unsurvivable dynamic events. The efficacy and validity of the survivability-based protection for $3\phi$ IMDs are verified through simulation and experimental tests. These tests are conducted for 10 hp $3\phi$ IMD under various types of dynamic events. Test results demonstrate the effectiveness of the survivability-based protection in responding to unsurvivable dynamic events to prevent damage to different components in a $3\phi$ IMD. [ABSTRACT FROM AUTHOR]

This article presents the performance evaluation of the frame-angle-based (FAB) direct torque controller (DTC) for 3φ induction motor drives (IMDs), which are fed by 3φ six-pulse wavelet-modulated (WM) dc–ac power electronic converters (PECs). The tested DTC is designed to adjust the de- and qe-axis components of the voltages (veds and vegs) applied to a 3φ IMD. The adjustments in veds and vegs are created in response to changes in the load torque, command torque, drive speed, and/or system parameters. Desired adjustments in veds and vegs are set by regulating the angle θ of the frame created by veds and vegs. This frame produces reference modulating signals that are required to generate WM switching pulses for operating the 3φ dc–ac PEC in the IMD. The complete IMD system, incorporating the FAB-DTC, is implemented for a 10-hp IMD system for performance evaluation. Tests of the FAB-DTC for the 10-hp IMD are conducted for various changes in the load torque, command torque, drive speed, and system parameters. Simulation and experimental test results demonstrate fast, accurate, reliable, and dynamic responses with minor sensitivity to variations in system parameters. [ABSTRACT FROM AUTHOR]

This article presents and tests the performance of a digital differential protection for three-phase (3φ) converter transformers. The proposed digital differential protection is developed to comply with the ANSI 87T protection procedure. The presented protection is featured with fault detection based on the energy contents of the high-frequency subbands of the d−q axis components of differential currents. Desired energy contents are extracted using the phaselet transform (PHT), which can process signals without sensitivity to the variations in their phase shifts. Energy contents of the high-frequency subbands offer accurate, fast, and reliable detection, and identification of internal faults in any part of a 3φ converter transformer. The d−q PHT-based digital differential protection is implemented for performance evaluation using different 3φ converter transformers, when feeding controlled rectifier units. Performance results demonstrate accurate, fast, and reliable detection, and response to different types of fault, and nonfault events. Response features of the developed differential protection are complimented with simple implementation, reduced computations, and minor sensitivity to phase shifts, fault location, and loading levels. [ABSTRACT FROM AUTHOR]

This article presents a method to include fault currents in the reliability analysis of motor drives. The presented method is based on formulating a fault current matrix (FCM), the elements of which are values of the currents flowing in all parts of a motor drive. The FCM is processed using the principal component analysis (PCA) to determine the pattern of variations in all currents due to any failure event. The output of the PCA is used to determine the failure rates for all parts of a motor drive. Determined failure rates can provide a tool to set an adequate action (mitigation, maintenance, or shutdown) to ensure a reliable and safe operation during and post any failure events experienced by the motor drive. The validity and accuracy of the PCA-FCM method are verified by employing it in the reliability analysis of different motor drives with different ratings. Results demonstrate the advantages of including fault currents in setting adequate actions in response to possible failure events. [ABSTRACT FROM AUTHOR]

This article develops, implements, and tests a method for selecting the locations and sizes of battery storage systems (BSSs) for power systems with distributed power generation. The developed method is based on calculating the coherency index for each bus to determine its contribution to the frequency of the center of inertia (COI) during and post a transient event. Once the coherency index is calculated for all buses, the principle component analysis (PCA) is used to identify the buses with consistent low values of the coherency index. These buses are considered as candidate locations for BSSs. In addition, the lowest values of the coherency index are used to determine the required sizes of BSSs to be connected at the buses with low contributions to the frequency of the COI. The performance of the PCA with COI (PCA-COI) method is evaluated for the Barbados power system for various transient events. Performance results show that BSSs (selected using the proposed method) can effectively improve the frequency stability with minor sensitivity to the levels of distributed power generation, loading levels, and/or type or location of transient events. [ABSTRACT FROM AUTHOR]

This article develops and tests a controller for residential electric water heaters (EWHs). The developed controller is operated to maximize the energy stored in EWHs during off-peak-demand times, in order to reduce their power demands during peak-demand times. Desired control actions aim to adjust the minimum temperature settings of EWHs using the unit commitment (UC). In order to eliminate the need for a direct measurement of EWH power demands, the bus-split (BS) aggregation method is employed. The BS method is employed due to its ability to extract the power demands of an EWH from household power meter readings. The UC is formulated using the energy stored in a EWH as a cost function, which is to be maximized during the off-peak-demand time. The solution of the UC problem is obtained using the Lagrange relaxation method that can offer fast convergence and reduced computations. The BS-UC controller is implemented for performance testing using power meter readings that are collected from 150 residential households during the fall, winter, spring, and summer seasons. Test results demonstrate the ability of the BS-UC controller to provide accurate and effective control of EWHs, which are complimented by a minor sensitivity to the number controlled EWHs, hot water consumption, and seasonal variations in residential load power demands. [ABSTRACT FROM AUTHOR]

Three-phase ($3\phi$) power transformers can have their windings configured to create local neutral points, which can be connected to ground. The grounding of a $3\phi$ power transformer is intended to limit ground currents (including fault currents) and limit ground potentials. These objectives can be translated into the resistive grounding that is usually designed based on system ratings and transformer parameters. The resistive grounding, however, can impact the flow of the harmonic components present in the exciting currents of a $3\phi$ power transformer. As a result, undesired harmonic components are induced in primary and secondary voltages. This article presents the design and performance of a frequency-selective grounding that can achieve the objectives of grounding a $3\phi$ power transformer. The developed grounding is designed to provide a resistive path for low-frequency currents (faults), and to create a low impedance path for high-frequency currents (harmonics). The frequency-selective grounding is experimentally tested for a $3\phi$ power transformer with different primary and secondary winding configurations, different fault types, and source grounding. Test results show that the developed grounding can reduce the ground potential, harmonic distortion in primary and secondary voltages, and ground fault currents with a minimum interference with ground fault protective devices. [ABSTRACT FROM AUTHOR]

Solid-state transformers (SSTs) have diverse designs and constructions that make them suitable for various industrial applications, including distributions systems. This new breed of transformers has been developed to support the typical functionalities of core-type distribution transformers, along with new functionalities, such as controlling power flows, integrating dc distribution systems, utilizing distributed generation and storage units, supporting load-side voltage/frequency control, and improving the power quality. As SSTs become candidates for distribution systems, their deployment can pose challenges for distribution systems. Such challenges include the cost, protection, size and weight, efficiency, and adequate grounding designs. This article discusses some of the challenges that face the deployment of SSTs in distribution systems. In addition, this article provides a comparison between core-type and SST transformers for applications in distribution systems. The comparison between the transformers is made in terms of their efficiency, cost, and weight. Finally, this article makes several recommendations for future works that can further facilitate the deployment of SSTs in distribution systems. [ABSTRACT FROM AUTHOR]

Solid-state transformers (SSTs) are an emerging technology that has been developed to improve the stability, reliability, and economic operation of distribution systems. These new transformers are composed of a medium ac voltage (MV) stage, a dc stage, and a low ac voltage (LV) stage. Passive and active dc links are used to construct the dc stage in SSTs in order to offer new functionalities, including hybrid (ac and dc) distribution, reactive power compensation, voltage/frequency regulation, power quality improvement, and distributed generation utilization. On one hand, a distribution SST has its ac stage connected to an MV level, which mandates specific power electronic converter (PEC) topologies, switching element capabilities, and filtering circuits. On the other hand, the dc-link stage has to provide isolation between the MV and LV levels, which requires the employment of isolated dc PECs. Part I of this work provides a review of SST designs and constructions (for deployment in distribution systems), in terms of the required technology, supported functionalities, and construction features. [ABSTRACT FROM AUTHOR]

This paper presents the online implementation and performance evaluation of the phaselet-based method for detecting electric faults in induction motor drives (IMDs). The online implementation of tested fault detection method is achieved using a digital signal-processing board, where the inputs are the 3φ stator currents and the output is a trip signal. The desired fault feature is extracted using six digital high-pass filters, whose coefficients have been obtained using phaselet basis functions that are generated by the biorthogonal 2.1 scaling function. The performance of the phaselet-based fault detection method is tested for two different IMDs that are fed across-the-line and through a frequency drive system, when operated at different loading levels. Experimental test results show accurate, reliable, and fast fault detection, along with negligible sensitivity to the speed, loading levels, IMD ratings, and fault type. [ABSTRACT FROM PUBLISHER]

This paper presents the analysis and development of a new method for electric fault detection in induction motor drives. The proposed method is based on extracting the magnitudes and phases of the high-frequency subband (HFSB) contents present in the d - q-axis components of the stator currents (id and iq) in an induction motor. The desired magnitudes and phases are extracted by processing id and iq using phaselet frames that are realized by a modulated filter bank. This filter bank is designed using six digital high-pass filters, whose coefficients are determined by biorthogonal phaselet basis functions. Extracted HFSB contents provide signature information that can offer accurate and fast detection of faults. The phaselet-based electric fault detection method has been made into a procedure for digital implementation. The performance of the proposed method is evaluated offline for collected stator currents from two different induction motor drives under different operating conditions. Offline test results show accurate, reliable, and fast detection of electric faults, with minor sensitivity to the ratings, loading levels, and type and location of faults. [ABSTRACT FROM PUBLISHER]

This paper presents the implementation and performance evaluation of a coordinated antiislanding protection for systems with multiple distributed generation units (DGUs). The proposed coordinated antiislanding protection is structured to process the d-q-axis components of the instantaneous three phase apparent powers (s_{d} and s_{q}) determined at the point-of-common-coupling for each DGU. The processing of sd and sq, for each DGU, is carried out by the wavelet packet transform (WPT) in order to extract their low- and high-frequency subband contents. The contents of WPT low- and high-frequency subbands offer signature information that can facilitate detecting the islanding condition and identifying the islanded DGU(s). The coordinated antiislanding protection is implemented in real time for experimental testing on a laboratory collector system that has three different DGUs. Experimental results reveal fast and accurate responses to islanding events, accurate identification of islanded DGUs, and negligible sensitivity to the type or ratings of protected DGUs. In addition, test results show that the $d-q$ WPT-based coordinated antiislanding protection can accurately distinguish between islanding and nonislanding events, including faults, step changes in power delivery to the grid, unintentional loss of grid connection, low-voltage ride through, and sudden harmonic distortion on the grid side. [ABSTRACT FROM AUTHOR]

This paper presents a coordinated anti-islanding protection for collector systems with multiple distributed generation units (DGUs). The presented anti-islanding protection is established based on processing the d-q-axis components of the instantaneous three phase apparent powers (s_{d} and s_{q}) determined at the point-of-common-coupling using the wavelet packet transform (WPT). Processing sd and sq by using WPT allows the extraction of low- and high-frequency sub-band contents. The contents of the high-frequency sub-band are used to detect and distinguish islanding events, and contents of the low- and high-frequency sub-bands are employed to define a coordination index, which is used to identify the islanded DGU(s). The presented anti-islanding protection is implemented for off-line testing using data obtained from a laboratory collector with four different DGUs. Off-line test results demonstrate accurate, fast, and reliable responses to islanding and nonislanding event(s), and accurate identification of islanded DGUs along with negligible sensitivity to levels of power delivery to the collector system. [ABSTRACT FROM AUTHOR]

The design and implementation of a Virtual Electric Power Transmission Line Lab for undergraduate curricula is introduced in this paper. The aim of the virtual laboratory is to enhance learning and teach students the basis and characteristics of the power transmission line model under different conditions in a virtual interface before entering the field. The user can realize various tests, such as short circuit, no-load, load and fault tests, to develop an understanding of the model behaviors, effects of changes in the model parameters, load and connections. The proposed Virtual Electric Power Transmission Line Lab is developed in the MATLAB graphical user interface (GUI) environment. The proposed virtual lab has been implemented in the Power Systems Lab taught at the Department of Electrical and Electronics Engineering at Karadeniz Technical University as part of the undergraduate curriculum. A survey of the students who took the lab course has been conducted, and the responses are included in this paper. [ABSTRACT FROM AUTHOR]

This paper presents the development and performance evaluation of a digital protection for interconnected distributed generation units (DGUs). The developed protection detects and responds to transient disturbances (fault and nonfault conditions) based on the magnitudes and phases of the high-frequency sub-band contents, which are extracted from the $d$–$q$-axis components of the currents flowing through the point-of-common-coupling (PCC). These magnitudes and phases are extracted by six phaselet frames that are realized by a modulated filter bank that is composed of six digital high-pass filters (HPFs). The coefficients of HPFs are determined by biorthogonal phaselet basis functions. Extracted magnitudes and phases of the high-frequency sub-band contents of PCC $d$–$q$-axis current components provide signature information for accurate detection and identification of faults. The performance of phaselet frames-based digital protection is experimentally tested for two wind energy conversion systems (WECSs) and a photovoltaic (PV) system under different fault and nonfault conditions. Test results demonstrate reliable and timely responses, along with negligible sensitivity to the type and control of DGUs, type and location of faults, and loading levels. [ABSTRACT FROM PUBLISHER]

In this study, a direct wheel drive electric vehicle based on an electronic differential system with a fuzzy logic sliding mode controller (FLSMC) is studied. The conventional sliding surface is modified using a fuzzy rule base to obtain fuzzy dynamic sliding surfaces by changing its slopes using the global error and its derivative in a fuzzy logic inference system. The controller is compared with proportional–integral–derivative (PID) and sliding mode controllers (SMCs), which are usually preferred to be used in industry. The proposed controller provides robustness and flexibility to direct wheel drive electric vehicles. The fuzzy logic sliding mode controller, electronic differential system and the overall electrical vehicle mechanism are modelled and digitally simulated by using the Matlab software. Simulation results show that the system with FLSMC has better efficiency and performance compared to those of PID and SMCs. [ABSTRACT FROM AUTHOR]

Design and utilization of a Virtual Photovoltaic Systems Laboratory for undergraduate curriculum are introduced in this paper. The laboratory introduced in this study is developed to teach students the basics and design steps of photovoltaic solar energy systems in a virtual environment before entering the field. The users of the proposed virtual lab will be able to determine the sizing by selecting related parameters of the photovoltaic system to meet DC and AC loading conditions. Besides, the user will be able to analyze the effect of changing solar irradiation and temperature levels on the operating characteristics of the photovoltaic systems. Common DC bus concept and AC loading conditions are also included in the system by utilizing a permanent magnet DC motor and an RLC load as DC and AC loading examples, respectively. The proposed Virtual Photovoltaic Systems Laboratory is developed in Matlab/Simulink GUI environment. The proposed virtual lab has been used in Power Systems Lab in the Department of Electrical and Electronics Engineering at Karadeniz Technical University as a part of undergraduate curriculum. A survey on the students who took the lab has been carried out and responses are included in this paper. [ABSTRACT FROM AUTHOR]