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In this paper we present a scalable approach based on the latency-based linear multistep compound method to use graphic processing unit (GPU) to accelerate the power system simulations with electromagnetic transients. To balance between the computational load and accuracy, we modeled the power system using shifted frequency analysis. Then, to efficiently exploit the hardware, our computational approach is designed to utilize both data-parallel and task-parallel execution. In addition, a graph-based thread safety design is introduced to achieve high scalability in the paralleled component computations. Furthermore, our implementation introduces a translation layer for different heterogeneous computing frameworks during compile time, so that a wide range of GPU devices can be supported without losing performance. Finally, benchmark results show that our approach achieves faster-than-real-time capability for systems with hundreds to thousands of nodes. [Display omitted] • Exploits data- and task-parallelism together in an automated way. • A graph-based approach to ensure thread safety to increase scalability. • A compile-time translation layer to allow execution on various platforms. • Faster-than-real-time for system with more than 10,000 dynamic components. • 82 × faster compared to an optimized sequential simulation. [ABSTRACT FROM AUTHOR]

Highlights • Variable renewable energy integration diminishes synchronous inertia of power systems, resulting in vulnerable frequency instability. • Alternative options of fast frequency resources are required for secure and stable grid operation under high penetration of renewables. • This paper provides a critical review of potential sources of fast frequency reserves, and way forward to maintain secure and stable grid operation. Abstract The last few decades have seen renewable energy source (RES) integration growing at a rapid pace and this trend is likely to continue. The displacement of conventional synchronous plant, particularly at higher RES shares, is resulting in a 'lighter' system with low system inertia and reduced governor droop stiffness, leading to increased vulnerability to fast frequency stability. This paper presents a review of literature from the research and industry communities on possible sources of non-synchronous fast frequency reserve, considered as a potential solution to address diminishing synchronous reserve in RES integrated systems. The wide range of potential sources includes wind turbines, solar photovoltaic plant, energy storage, high voltage direct current (HVDC) systems, and demand response. The challenges and limitations associated with each approach are highlighted, and alternative strategies to maintain a minimum volume of security constrained fast frequency reserve are discussed based on the recent industry trends. [ABSTRACT FROM AUTHOR]

Highlights • A reduced-order FEHD model approach. • Computational savings while keeping accuracy compared to traditional EHD and TD. • Harmonic modeling and simulation of a stand-alone PV-battery-supercapacitor hybrid system. • FEHD subsystems involving distinct integration time-steps (slow or fast dynamics). • Verification of the proposed approach via PSCAD/EMTDC software tool. Abstract Simulation of stand-alone photovoltaic (PV) systems requires mathematical models that permit to reproduce systems' dynamics closely to actual components. Such accuracy helps engineers to evaluate power quality issues, e.g., harmonic transient analysis and total harmonic distortion, and to design control algorithms to fulfill the applicable connection codes. This paper proposes a model, aimed at harmonic transient simulation, of a stand-alone PV system that involves a battery-supercapacitor hybrid energy storage system. The proposed model is based on a recently introduced harmonic domain modeling technique, i.e., flexible extended harmonic domain (FEHD). This paper demonstrates that the proposed FEHD-based model keeps accuracy of harmonics dynamics while diminishing computational burden compared to time-domain and conventional extended harmonic domain based models. Two case studies, involving the aforementioned hybrid PV system, are presented and validated against the PSCAD/EMTDC simulation tool. [ABSTRACT FROM AUTHOR]

Highlights • The paper presents a PMU-based autoreclosing method. • The paper presents a comprehensive auto-reclosing method for all fault types. • The proposed method can enhance the reliability of distribution systems. • Effects of thermal stress and stability indices are investigated before reclosing. • The proposed method has been evaluated using real-time HIL simulation method. Abstract This paper presents an adaptive auto reclosing scheme (AARS), applicable to active distribution systems, which are equipped with Phasor Measurement Units (PMUs). The scheme differentiates between temporary and permanent faults by taking into account the operational conditions of the network when determining the reclosing dead time. The performance of the proposed scheme is assessed through a real-time hardware-in-the-loop (HIL) simulation test setup. [ABSTRACT FROM AUTHOR]

This paper proposes a novel simultaneous control interface and protection scheme for DC microgrids (DCµG) interconnected systems, although the interconnections could be possible via two power electronic systems such as DC/DC converter. Each DCµG presented in this paper is supplied by AC grid as well as battery bank unit, distributed generation (DG) unit and AC load unit. The proposed control interface is based on a developed suitable small signal model for each DCµG that provides proper power flow control and cancellation of interactions between DCµG. Also, the presented protection scheme for fast fault detection in DC link is based on fuzzy inference system (FIS), so that faults could be detected as quickly as possible in few milliseconds. In fact, the aim of this paper is simultaneous protection and control interface for DC multi microgrids, so that the performance of the controller and protection system is separate, yet integrated together. As such, DC multi microgrid performance under different events, such as change in active power of DGs and short circuit is not in trouble and disorder. Simulation results indicate the remarkable effectiveness of the proposed control interface and protection scheme for DCµG interconnected systems. For validation of the capability and feasibility of FIS fault detection scheme, simulated network and protection algorithm are implemented in laboratory-scale. The implementation results demonstrate that FIS protection scheme can swiftly detect faults within a few milliseconds. [ABSTRACT FROM AUTHOR]

IEC61850 protocols aim to reduce the data management with a bandwidth that does not present any issues. Fast tripping protection schemes using IEC 61850 will lead to network flooding, high delay, and reduced network security. The study provides propagation characteristics of traveling wave with extra high-speed busbar protection in compliance with IEC 61850 technique. This paper analyzes the process bus and suggests two methods in order to achieve the intended fast protection with IEC 61850. The simulation of the suggested methods based on the OPNET Modeler has proven that these methods can solve the network flooding problem in Ethernet and band-limited channels such as WLAN. This study will pave the way for researchers to reuse the traveling waves for fast protection with IEC 61850. In this paper, the simulation results of the case study busbar protection using transient signal (traveling wave) based on IEC 61850 network system configurations using OPNET Modeler simulation software were presented and the influence of data rate, a number of MUs sharing process bus and delay characteristics of these system configurations were evaluated. [ABSTRACT FROM AUTHOR]

The commonly used protection scheme for turn-to-turn faults detection of shunt reactors lacks sensitivity when applied to thyristor controlled transformer-type controllable shunt reactor (TCT-CSR), especially when TCT-CSR is working almost at its rated power and the short-circuited turn ratio is small. Based on the analysis and comparison of the characteristics under internal faults and external faults, this paper proposes zero-sequence overcurrent protection with zero-sequence voltage blocked to detect turn-to-turn faults within control windings. The impacts of power regulation on the proposed protection scheme is investigated in depth. The results indicate that the proposed protection scheme may mal-operate during power regulation. As a solution, the approach of increasing the resistance of control windings is proposed in this paper. The value of resistance and its impacts on the performance of the proposed protection scheme during power regulation are discussed in detail. Finally, the optimal value of the resistance of control windings is recommended as the reference for the future design of TCT-CSR after the comparison of simulation results under different scenarios. [ABSTRACT FROM AUTHOR]

This paper presents a novel dynamic clustering equivalent modeling method for a two-staged photovoltaic (PV) station cluster, which is a key tool to analyze the dynamic responses of the distribution network with high PV penetration. In this paper, a dynamic affinity propagation (DAP) clustering algorithm is proposed after studying the indexes that can describe the dynamic characteristics of two-staged PV power station. Then this algorithm is used to group the PV stations in the PV cluster according to their dynamic characteristics. Finally, the dynamic equivalent model of PV cluster is obtained by parameters aggregation of PV stations in the same group and simplification equivalent of the network. The proposed method is verified by a PV cluster distribution network with 20 two-staged PV stations and the simulation results show that the proposed dynamic equivalent model can accurately reflect the dynamic response characteristics of the PV cluster. At the same time, the simplified PV cluster model would reduce the computational complexity and the simulation time significantly. [ABSTRACT FROM AUTHOR]

This paper presents a new droop-based control strategy for hybrid microgrids (HMG) with improved power sharing. When ac microgrids (AC-MG) and dc microgrids (DC-MG) are present in a distribution grid, there is an opportunity to interconnect them via an interlinking converter (IC) and form a HMG. Power sharing and adequate voltage/frequency control are the main functions of AC-MG and DC-MG control systems in standalone mode. When it comes to a HMG, active power sharing throughout the whole system must also be properly achieved by controlling the IC active power throughput. Furthermore, the possibility of participation of IC in AC-MG reactive power adds some complexity to a HMG control system. In this paper, a new decentralized control strategy is presented for a HMG which relies on regulating the voltage magnitude of a common bus in each microgrid. In this regard, new droop characteristics for sources across both microgrids as well as IC are proposed. The proposed droop characteristics result in better active/reactive power sharing across both microgrids and at the same time results in better voltage regulation. The derivation of new droop characteristics is thoroughly discussed in this paper. Simulation results are used to show the improvement achieved. [ABSTRACT FROM AUTHOR]

Interruptible load management (ILM), as an important incentive-based demand response (DR) program, plays a critical role in power system operation. An improved ILM scheme design method is proposed in the paper. From the perspective of social welfare, the scheme design is described as an optimization problem, and then mechanism design theory is adopted for solving. The novel idea presented in the paper is that the customer baseline load (CBL) is used to parameterize the type of customer (TOC), which is fundamental information for application of mechanism design theory. Being private information, TOC is not directly attainable, but CBL can be estimated based on historical load data (namely the customer performance), and it can reflect the customers’ rational judgments in self-benefit decisions. Firstly, the validity of adopting CBL to determine TOC is demonstrated. Then, the load curtailing potential constraints and the objective function are rebuilt in the expression of CBL correspondingly, so that the mechanism design theory successfully works with CBL instead of TOC. Moreover, adjustment strategies are also proposed to cope with the possible unenforceable scheme scenarios, thus the practicability of the designed scheme is ensured. Finally, simulations are carried out to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

• A novel Coordinated Cyber-Physical Attacking (CCPA) mode on power grids. • Full malicious power dispatch based on false command injection by maximizing inverse-community characteristic as objective to quantify vulnerability of the system. • Partial malicious power dispatch as the measure in CCPA. • Demonstration of the proposed novel CCPA mode. This paper proposes a new mode of cyber-physical attack based on injecting false commands, which poses an increasing risk to modern power systems as a typical example of Cyber-Physical Systems (CPS). Such attacks can trigger physical attacks by driving the system into vulnerable states. To address the critical issues arising from this new mode, we define an inverse-community (IC) in power flow distribution and evaluate it using inverse-modularity. To identify the most vulnerable state of the IC that represents the inherent vulnerability of the system, we employ a full malicious power dispatch problem. We also analyze an example of the proposed mode, where a partial malicious power dispatch that maximizes inverse-modularity is combined with physical attacks aimed at disconnecting vulnerable IC boundary lines, making cascading failures highly likely. To demonstrate the potential impact of this coordinated cyber-physical attack, we use the IEEE-118 and IEEE-300 bus systems for simulation. The results show the effectiveness of this attack strategy and provide a new perspective to analyze cyber-physical security issues in modern power systems. [ABSTRACT FROM AUTHOR]

The increasing presence of inverter-based distributed generation (DG) units in microgrid application requires control methods that achieve high performance not only during normal operating conditions, but also under unbalanced conditions. These conditions can occur permanently due to distribution of unbalanced loads on the three phases of the microgrid. This paper proposes a robust control strategy for a grid-connected multi-bus microgrid containing several inverter-based DG units. Each of the DG units can supply a combination of balanced and unbalanced local loads. The proposed control strategy employs an adaptive Lyapunov function based control scheme to directly compensate the negative-sequence current components caused by unbalanced loads in some part of microgrid; and a sliding mode based control scheme to directly regulate the positive-sequence active and reactive power injected by DG units to the microgrid. The control method proposed in this paper is shown to be robust and stable under load disturbances and microgrid parameter uncertainties even in the presence of nonlinear and time-variant unbalanced loads. The effectiveness of the presented controller is validated through time-domain simulation studies, under the MATLAB/Simulink software environment. [ABSTRACT FROM AUTHOR]

In this paper a power injection model is presented for the Generalized Unified Power Flow Controller (GUPFC), which facilitates its representation in the electric power system (EPS). This model of the GUPFC device becomes an attractive option to be implemented in power flow and optimal power flow programs. An efficient structure for the GUPFC control system is also presented in the article. This can be used to represent the dynamics in both stability analysis of small perturbations, which is the focus of this work, and in transient stability analysis (large disturbances) of the EPS. Considering the most basic GUPFC configuration, the proposed structure can control four active and reactive power flows in two lines, the voltage at the common installation bus; addition to these characteristics inherent in the GUPFC, this device can provide damping for the electromechanical oscillations of the EPS, as a POD (Power Oscillation Damping) controller is coupled to the control loop. Simulations are performed on one multimachine test system, whose results are analyzed and discussed in this paper, in order to analyze the performance of the power injection model and its proposed control structure in the damping of oscillations. [ABSTRACT FROM AUTHOR]

Despite the advantages of matrix converters (MCs) compared with standard voltage source converters (VSCs), all of the direct power control (DPC) strategies for doubly fed induction generator (DFIG) reported in the literature, only utilize VSCs. In this paper, the influence of MC voltage vectors on active and reactive powers variation is investigated. Compared with VSCs, MCs generate higher number of voltage vectors. Using this inherent advantage of MC, the main contribution of this paper is to reduce large active and reactive power ripples which is one of the main drawbacks of conventional DPC method. Utilizing a wide range of voltage vectors with different amplitudes, a new switching table is derived which using this table, not only large power ripple is compensated but also, a close to unity input power factor for MC can be achieved. In the other word, the presented scheme adds the advantages of MC and DPC together. Moreover, Owing to the operation of MC in direct ac-ac form, the presented scheme effectively eliminates the need for the grid side converter used in conventional DPC, which has a complicated control method is eliminated. Simulation results show the effectiveness of the proposed method and have a reasonable correspondence with theoretical and mathematical analysis. [ABSTRACT FROM AUTHOR]

This paper presents the binary group search optimization algorithm (BGSO) for solving the optimal distribution network reconfiguration problem. The objective of the optimization is loss reduction in distribution system. The proposed GSO algorithm is introduced with fundamental modifications, such as introducing binary form of the GSO in order to be fit for reconfiguration and all binary form problems. All formulation of conventional GSO has been modified for accessing a novel powerful binary searching algorithm. Additionally, the forward-backward sweep, load flow is used in this paper, due to its accuracy. The Comparative studies are conducted on standard networks to verify the validity of the proposed algorithm. The simulations on different test cases confirm validity of the BGSO in solving optimal distribution network reconfiguration problem. [ABSTRACT FROM AUTHOR]

Highlights • Considering the dependency of the eddy current loss on peak induction in the transformer model. • Studying the impact of considering the eddy current in the lamination on ferroresonance mode at critical points. • Investigate the stability of ferroresonance modes regarding the initial switching time. • The experimental validation of the simulation results. Abstract The susceptibility of ferroresonance to the eddy current in the iron core is presented in this paper. The stability of ferroresonance modes is investigated regarding to the eddy current in the core lamination. The impact of switching time on ferroresonance oscillations was done via a basin of attraction by identifying the initial points that can be encountered during transformer operation. An accurate dynamic model of transformer was implemented taking into account the dependence of frequency and peak induction. The experimental results are predicted using the implemented model with and without taking the effect of eddy current in the lamination. The comparison was made between the experimental results and the computed ones. It shows the necessity of considering the dependency of the iron losses on peak induction for an accurate predicting of ferroresonance behaviour at critical points. [ABSTRACT FROM AUTHOR]

This paper proposes a simple approach to design fractional-order (FO) controller via internal model control (IMC) technique for load frequency control (LFC) problem in power systems. The proposed scheme utilizes the concept of CRONE principle, model-order reduction and FO filter in IMC framework to derive a robust controller. Initially, the scheme is applied to single-area power system and then extended to two-area interconnected system. The turbines considered are non-reheated, reheated and hydro type; and physical constraints of turbine and governor are also taken into account to validate the applicability in more realistic environment. Simulation results show that it can bring improved disturbance rejection performance in nominal condition as well as in presence of uncertainties and constraints in plant parameters. [ABSTRACT FROM AUTHOR]

In this paper, the model predictive control (MPC) system based on the state space is designed to generate the appropriate switching pulses for UPS inverters. The fast dynamic response and the capability in assessment of various cost functions are some advantages of the predictive control system. The equations concerning the control system show that the load current should be measured. To eliminate the required sensor for load current measurement a new observer is proposed, so the amount of cost can be reduced and the reliability of the system also enhanced. Ordinary observers like Luenberger in terms of stability and design encounter several difficulties. The proposed observer is developed based on Fourier series and instantaneous power theories. This observer is doing well in estimating the load current and renders superior performance regarding the dynamic behavior, stability and convergence. Furthermore, in this observer there is no need for any parameters adjustment and the load current is accurately observed using the measured output voltage and the filter current. To examine the operation of the system the necessary simulations and laboratory experimental results are provided on a 3-phase 220 V UPS. The obtained results are then compared to those obtained by the Luenberger observer. [ABSTRACT FROM AUTHOR]

This paper presents a new concept of Static Synchronous COMpensator (STATCOM) based on a Hybrid Cascaded Multilevel Converter (HCMC). The HCMC consists of a two- level voltage converter and a wave-shaping circuit formed by cascaded H-bridge Sub-Modules (SM). Firstly, the operation principle and overall control strategy of HCMC are presented. After that, some key parameters including size of capacitors, numbers of sub-modules are in-depth analyzed. And then, a thorough comparison between the proposed HCMC-based STATCOM and conventional cascaded H-bridge based STATCOM is made, which turns out that the proposed HCMC-based STATCOM requires less number, size and stored energy of capacitors and has less power loss. Finally, a 35 kV/±50 Mvar HCMC-based STATCOM simulation model is constructed in PSCAD/EMTDC software platform. The simulation results validate the feasibility of the proposed HCMC-based STATCOM and the correctness of the analysis. [ABSTRACT FROM AUTHOR]

Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) has received much attention in the recent years due to its merits of no fossil fuel consumption, low costs, fast start-up and wide-ranging part load ability. It is considered to have a variety of power gird applications including providing reserve services. Although a number of studies are reported in the optimal scheduling strategy of using compressed air energy storage, very few studies have been reported in AA-CAES reserve capacity modelling. This paper presents a reserve capacity model for an AA-CAES facility considering its working mode conversion process, the dynamic characteristics, the air pressure limitations, the thermal storage capacity limitations and the power output limitations of AA-CAES. The developed reserve capacity model is then used in the power system optimal joint energy and reserve scheduling. In the scheduling, the limits on the reserve capacities of Thermal Power Units (TUs) and Interruptible Loads (ILs), which are caused by AA-CAES, are taken into account. The developed scheduling model are used to analyse the impacts of AA-CAES on the system energy and reserve schedules, the system operation costs and the wind curtailment. Numerical simulation results indicate that the participation of AA-CAES in power system operation does not only reduce the system energy and reserve costs, but also mitigate the wind curtailment. However, it is found that AA-CAES is unsuitable for undertaking the system reserve demand alone and using AA-CAES to provide reserve services may increase the system total reserve demand. [ABSTRACT FROM AUTHOR]

With the high voltage direct current Transmission (HVDC) booming, HVDC grid has received wide attention. As an essential component in HVDC grid, high voltage direct current circuit breakers (DCCB) requires urgent and intensive study. A novel topology for current limiting DCCB (CL-DCCB) is proposed in this paper. The topology consists of several units which are divided into two classes: main circuit breaker (MCB) and branch circuit breakers (BCBs). The number of inductor branches can be flexibly selected to enhance the current limiting effect. The CL-DCCB can start current limiting operation when a suspected fault occurs. When the detection circuit reveals what has happened, it can be determined whether to implement breaking operation or recover to normal state. This mode allows longer fault detection time and circuit breaker operation delay while guaranteeing the fault current within the maximum limit of the system. Finally, Simulation model and experiment prototype are built to study the design criteria for CL-DCCB. It is observed that the maximum detection delay can be extended to 12 ms. Moreover, the current limiting effect can be enhanced when the number of inductor branches or the inductance of each branch is increased. [ABSTRACT FROM AUTHOR]

Both Flexible AC Transmission System (FACTS) devices and energy storage may provide benefits to the power system, e.g. reduced transmission losses, improved system stability, voltage regulation and reduced congestion. As a result, FACTS devices can diminish the value of the installed energy storage and vice versa. In order to assess their impact on each other, this paper formulates a unit commitment model that includes generic energy storage and FACTS devices in order to investigate characteristics of their joint operation assess how they cancel out each other’s benefits. The results of four unit commitment models are presented: (i) with no storage or FACTS devices (base case); (ii) with FACTS devices only; (iii) with energy storage only; (iv) with both FACTS devices and energy storage. An analysis of the benefits of both technologies is performed and economic assessment is presented. The simulations are performed on IEEE RTS96 system using CPLEX 12 under GAMS. [ABSTRACT FROM AUTHOR]

Efficient provision of electricity requires timely expansions of power transmission capacity. However, regulation does not always send the right signals to generate the required (and timely) investments. Therefore, it is important to evaluate the effect of alternative regulations on investment on transmission capacity. In this paper, considering regulated remuneration, we perform this evaluation with a behavioral simulation model of the transmission capacity expansion, in which capacity is endogenously determined by the demand/supply relation. Two planning approaches were considered: centralized planning where the investments are fully coordinated by a central organism, and decentralized planning where the capacity expansions are driven by the investors’ rationality on the power market evolution. The model is applied to the Colombian case. The decentralized approach has lower costs (usage charges) than centralized expansion, but lower transmission capacity margins. As low transmission capacity margins create supply risks in high demand periods, regulators can increase coordination in decentralized planning by directly promoting investments that increase security of supply. [ABSTRACT FROM AUTHOR]

This paper proposes a framework to determine capacity profiles in smart buildings. In this scheme the users choose a level of power capacity to account for their stochastic demand while paying the corresponding electricity prices through a flexible time-and-level-of-use pricing policy. We formulate a two-stage stochastic optimization model that minimizes the total cost of booking a power capacity level and meeting the energy demand for the planning horizon. We present two approaches to select the scenarios for the stochastic optimization. In the first approach, we assume that the probability distributions of the start times of the loads are known, and the scenarios are generated using those distributions. In the second approach, we assume that only historical consumption data is available and we propose a new algorithm to build the scenarios using this data. Our simulation experiments validate the performance of both approaches and report cost savings of up to 16%. [ABSTRACT FROM AUTHOR]

Distribution system operators may in the future control active power of selected consumers and generators in order to achieve a desired grid behavior. For cost efficient deployment, this control application may use existing communication infrastructure with non-ideal properties, i.e. imposing delays and losses. This paper considers a control strategy for this use-case, called Active Power Reference Tracking, and investigates its performance for a realistic grid scenario with non-ideal communication using a Real-Time Co-domain Testbed and extensive simulation experiments. Results from the distributed implementation in the testbed show the effectiveness of the controller and that the considered scenario of the reference tracking application is not significantly affected by delays and losses as originating from PLC communication in good conditions. The subsequent simulation experiments show the resilience of the reference tracking control application to end-to-end message delays up to the order of 3 control periods and to message loss up to approximately 70%. [ABSTRACT FROM AUTHOR]

Low-voltage ride-through (LVRT) is the core of grid code requirements for grid connection of wind farms (WFs). This paper presents a capacitive DC reactor-type fault current limiter (CDRFCL) for LVRT capability enhancement of doubly-fed induction generator (DFIG)-based WFs. The CDRFCL is based on the conventional DC reactor-type fault current limiter (DRFCL), which is modified to overcome its limitations of operation and is adapted with the WF environment. To check the effectiveness of the proposed CDRFCL, its performance is compared with the series dynamic braking resistor (SDBR). The WF is modeled with equivalent aggregated DFIG. The PSCAD/EMTDC simulation results show that the CDRFCL is an effective solution for enhancement of LVRT capability and limitation of fault current contribution (FCC) of WFs. [ABSTRACT FROM AUTHOR]

In order to solve the problem of path protection for multicast services and improve the wavelength utilization ratio in substation communication networks (SCN), a p-cycle based protection scheme with cycle multiplexing and capacity balance (PBCM-CB) is presented in this paper to protect the multicast services under single link/node failure scenario. By analyzing the multicast services in SCN, the classical Prim algorithm is improved to generate optimized multicast light-trees corresponding to multicast requests. Based on this, the heuristic p-cycle generation algorithm is designed to connect the destination nodes of the multicast tree to a cycle to protect the entire tree. Aiming to improve utilization efficiency of the protection resource, the multiplexing conditions of the p-cycles are studied, and by multiplexing the existing p-cycles configured in the network, the wavelength utilization ratio is raised. Besides, in order to decrease the blocking probability (BP) of the network, a capacity balance strategy is adopted to generate the multicast trees and p-cycles. Simulation results demonstrate that the proposed algorithm can significantly reduce the redundancy and blocking probability of SCN compared with the existing flow p-cycle protection schemes. [ABSTRACT FROM AUTHOR]

The main protection of block transformer units is usually realized with use of differential relays. For back-up protection distance relays are mostly employed. Their second and third zones provide also coverage of faults along the adjacent line connecting the power plant with the nearest substation. This paper deals with a challenge related to proper impedance measurement across the transformer for the configurations where the currents from the HV star terminals are not available. Commonly used algorithms of the distance relays may be prone to serious under-reaching in such situations, which calls for a new approach with correction of the measurement procedure. The inclusion of zero-sequence current is proposed, and the improved protection algorithm is analyzed theoretically and thoroughly tested with the signals obtained from EMTP-ATP simulations. Rules for new protection settings are also provided. [ABSTRACT FROM AUTHOR]

One of the most important processes during load restoration is to use a suitable sectionalizing scheme to enhance the stability, especially when two islands are synchronized. In this regard, this paper provides a new scheme for the coordination of sectionalizing and load restoration to enhance the power system performance before and during the synchronization of islands. In doing so, there will be contradictory objective functions including maximizing the quality of sectionalizing process, minimizing the maximum standing phase angle (SPA) between islands, and minimizing the sum of energy not supplied (ENS) with unavailable energy capability (UEC) between all N-1 contingencies. Therefore, a multi-objective problem is defined as a mixed integer non-linear problem (MINLP). Also, a reliability-based index is defined to determine the quality of each island. Then, the θ-based water cycle algorithm (θ-WCA) is used to obtain the best Pareto optimal set. Two IEEE 39-bus and 118-bus power systems are used for validating the proposed method. The simulation results imply that the system can benefit from this scheme not only to have the good quality of sectionalizing, but also to enhance the power system performance during load restoration and the synchronization of islands. [ABSTRACT FROM AUTHOR]

The concept of microgrids has been introduced to facilitate the integration of the distributed energy resources (DERs) into distribution networks in a more economical, reliable and environment-friendly manner. One of the critical challenges associated with microgrids is devising an appropriate protection strategy. This is because the fault current level continuously varies owing to the existence of DERs and to the fact that the microgrid can operate in grid-tied and islanded modes. This paper proposes a new protection strategy for microgrids using an interval type-2 fuzzy logic system. The proposed strategy considers various uncertainties associated with faults and employs two different fuzzy systems to detect, classify, and locate the faults in microgrids. The phase angle between superimposed modal voltage and modal current is used as an input to the fuzzy system designed to identify the fault direction. The significant feature of the proposed strategy is that it can protect the microgrid after a single-phase tripping event. To validate the effectiveness of the proposed strategy, we have performed extensive simulations using MATLAB/SIMULINK. The simulation results show that the proposed strategy can detect, classify, and isolate various faults in the microgrid. Moreover, the strategy also provides backup protection in case of failure of the primary protection. [ABSTRACT FROM AUTHOR]

In distribution networks, the lack of measurement data is usually thought to be an inevitable bottleneck of conventional grid operation and planning. Recently, the availability of smart meters in the distribution network has provided an opportunity to improve the network observability. In medium-voltage (MV) distribution networks, there is an increasing demand to use aggregated smart meter data for the state estimation, instead of adopting pseudo-measurements with a low level of accuracy. However, the performance of an estimator requires good knowledge of the available measurements, in terms of both expected values and associated uncertainties. Therefore, this paper intends to firstly pave a new way of utilizing smart meter data gathered from the low-voltage (LV) feeders in a concrete and reliable manner. For the purpose of state estimation in MV distribution networks, smart meter data is to be processed through three steps: phase identification, data aggregation and uncertainty evaluation. The feasibility of the proposed method is verified on the IEEE European LV Test Feeder with a set of real-world smart meter data. Afterwards, the influence of the aggregated smart meter data on the three-phase state estimation are investigated on the modified IEEE 13-node test system and IEEE 34-node test system. Simulation results show that the effect of aggregated smart meter data on the accuracy of state estimators is dependent on both the accuracy level of the aggregated data and the measurement configuration in the network. Furthermore, the use of aggregated smart meter data is shown to be able to provide improved state estimation. [ABSTRACT FROM AUTHOR]

In this paper, a new single-ended travelling wave-based protection scheme for double-circuit lines is proposed. It is developed to operate in parallel with traditional phasor-based protective relays and is able to accelerate the tripping time in most fault scenarios. The proposed method considers the propagation of travelling waves in a loop formed by the faulted and healthy line circuits. Disturbances within a given protected zone can be reliably detected according to the amplitude, polarity and time difference between the arrival instants of travelling waves that reach the monitored terminal. Also, the accumulative cross-differential current deviation is used to confirm internal faults, distinguishing them from other non-fault events. From the analysis of massive digital fault simulations and actual field records, it is attested that the proposed protection is feasible and effective. [ABSTRACT FROM AUTHOR]

With the continuous development of distributed generation technology, the permeability of wind, solar and other renewable energy continues to increase. As a new kind of voltage control device, electric spring can suppress the voltage fluctuation caused by the power change of distributed generation effectively. In this paper, based on the analysis of the principle of voltage stability control for the electric spring, the optimization of control effect and non-critical load change are taken into consideration. Combined with advanced particle swarm optimization algorithm and fuzzy control algorithm, a method of voltage control for electric spring based on adaptive PI control is proposed, and the digital simulation is carried out. The simulation results show that the adaptive PI control has better voltage regulation effect than the traditional PI control, and can solve the adverse effect of the load variation on the electric spring. [ABSTRACT FROM AUTHOR]

Smart grid system protection can be divided into wide area network, WAN, and substation area protections. The IEC 61850 Ed.1 standard contains models for SV and GOOSE messages that can be used in intra-substation protection. This paper investigates the WAN and substation area protections based on a travelling wave with IEC 61850 that have not been used in a product since 2016. The high sampling frequency for processing the travelling wave may block the communications channel and reduce security. In order to address this problem, an approach is proposed that is based on using real-time travelling wave signal packing with lossless compression and travelling wave feature extraction. The performance of these techniques has been tested using an OPNET modeler, while their validity has been tested through computer simulation. The application of WLAN based on transient travelling wave for real-time protection has also been investigated. The lower sampling, or transformed, data can be used for the applications of transient waves in digital substations. The comparison protection based on travelling wave between the Ethernet and second-generation WLAN results has also been discussed. An IED design is proposed for fast tripping that can be used in WAN protection based on the travelling wave. This work paves the way for other research to start developing fast protection systems based on travelling wave with IEC 61850. [ABSTRACT FROM AUTHOR]

Ferroresonance, excited by saturated electromagnetic voltage transformers, can severely damage power systems because it produces long duration large overvoltages. In this paper, a method is developed to eliminate potential transformer (PT) ferroresonance through a model-free method. First, a structural diagram of the ferroresonance eliminating device is established based on a practical ferroresonant circuit. The effect of the adjustable parameters of the device is investigated, including resistance, pulse frequency, and pulse duty cycle. Then, Iterative control strategies are developed to adjust the gate signal duty cycle of the controller for limiting the ferroresonance to a normal status and then switching off the elimination device. Finally, simulations are conducted demonstrating that the method proposed was effective. [ABSTRACT FROM AUTHOR]

All available Pulse Width Modulation (PWM) techniques employed to different Matrix Converter (MC) topologies generally generate switching Common-Mode Voltage (CMV), which introduces numerous operational concerns in electric drives. Although a body of research for the three-phase case has been undertaken to either reduce or eliminate CMV, corresponding discussions for multiphase MC remain scarce. Interestingly enough, the three- to five-phase (3 × 5) Indirect MC (IMC) is a potential converter topology for five-phase based high power motor drives. In this paper, the different available switching states of a 3 × 5 IMC are classified based on their corresponding CMV levels. Accordingly, two different Space Vector Modulation (SVM) techniques are proposed, which can successfully reduce the peak CMV by 28% and 48%, respectively, when compared with the conventional modulation strategy, while the same maximum Voltage Transfer Ratio (VTR) is preserved. Although the 28% reduction has been alternatively achieved in literature based on carrier-based PWM, the 48% reduction attained in this study represents the maximum achievable reduction for this MC topology. The main concept is firstly introduced; then, both simulations and experiments are used to validate the proposed schemes. [ABSTRACT FROM AUTHOR]

Among different forms of wind energy technologies, doubly fed induction generator (DFIG) has been one of the most growing one during recent years. According to the updated grid codes, wind energy resources are needed to stay connected to the network during and after faults. To improve zero or low-voltage ride-through (LVRT) capability of DFIG, a control approach is proposed in the paper. The input signals of the proposed control approach are obtained by using state estimation technique. Since the dynamic behavior of the rotating speed of the stator flux can be considered in this method, it can minimize transient rotor current during and after clearing fault. Furthermore, the employment of state estimation method can minimize the effect of probable noise level in metering devices which is another advantage of this method. Simulation studies are done in a numerical case study to confirm the advantages of this method. [ABSTRACT FROM AUTHOR]

This paper sets out to explore and promote the use of a hydrokinetic microturbine module designed to obtain energy from water streams. It is made up of a hydrokinetic rotor, a permanent magnet generator, power electronic stages and a microcontroller to regulate power production. It is further complemented by a control strategy focused on maximizing the electrical power produced when varying different water velocities. This method is based on three operating zones defined by the electrical frequency produced by the generator, and where different values of direct current set points are defined. It is set in motion in a boost converter power stage, using a maximum current control, with constant off time in the power switch, and continuous or discontinuous mode of operation depending on the current value required. The control strategy has been validated though the use of dynamic simulations. The microturbine modules are suitable for alignment in rows to increase the power produced. The modules connected in smart grids define the hydrokinetic smart grid concept. A global control strategy for hydrokinetic smart grids has also been proposed and tested. [ABSTRACT FROM AUTHOR]

Semi-Definite Relaxation (SDR) techniques for AC optimal power flow (OPF) have recently been proposed as a means of obtaining a provably global optimal solution for many IEEE benchmark power systems. Solving the resulting semi-definite programs (SDP) can, however, be computationally intensive. Therefore new algorithms and techniques that enable more efficient computations are needed to extend the applicability of SDP based AC OPF algorithms to very large power networks. This paper proposes a three-stage algorithm for AC OPF based storage placement in large power systems. The first step involves network reduction whereby a small equivalent system that approximates the original power network is obtained. The AC OPF problem for this equivalent system is then solved by applying an SDR to the non-convex problem. Finally, the results from the reduced system are transferred to the original system using a set of repeating optimizations. The efficacy of the algorithm is tested through case studies using two IEEE benchmark systems and comparing the solutions obtained to those of DC OPF based storage allocation. The simulation results demonstrate that the proposed algorithm produces more accurate results than the DC OPF based algorithm. [ABSTRACT FROM AUTHOR]

This paper proposes a novel intelligent algorithm for fault location on the voltage sourced converter-high voltage direct current (VSC-HVDC) system. This method with single-ended measurement makes full use of frequency, time and energy to capture the fault features via Hilbert-Huang Transform (HHT). The time delay, characteristic frequency, energy attenuation and high-frequency energy are used as the input of ε-support vector regression (SVR) to get fault distance. Then bat algorithm (BA) optimizes the parameters of the model with cross validation comparing with other optimization algorithm. Furthermore, high-frequency variance contribution rate (HVCR) is adopted to identify the fault area. The VSC-HVDC simulation system is constructed to verify the reliability and accuracy of the method and the expected accuracy of the proposed method is ±500 m. The results demonstrated that the proposed method still has reliability and accuracy for hybrid transmission line with a small amount of data. [ABSTRACT FROM AUTHOR]

High Impedance Faults (HIFs) have been labeled as the most common disturbances in the power distribution systems. The special circumstances created by these faults mislead traditional protection equipment. The low magnitude and unpredictable nature of current correspond to many false detections and operators distrust in available installed protection schemes. Moreover, the nowadays harmonic rich content of distribution grids plays a significant role in increasing confusion for protection relays. The FFT approach has been utilized as an adequate detector of HIFs in regards to typical linear loads. The majority of available methods neglect the presence of non-linear loads. In the presented paper, a modified scheme has been engineered to compensate for this fact. The harmonic analysis of the sum of all three phase currents has shown to be a better substitute for the traditional feeder current. Numerous simulations via the IEEE 13-Node distribution system and experimental data analysis of “Palash” distribution system have shown promising results. The proposed scheme has shown to be capable of detecting and distinguishing between HIFs and normal events, i.e. capacitor bank and load switching. The presence of non-linear loads has been effectively detected and isolated from the procedure of HIF detection. [ABSTRACT FROM AUTHOR]

This paper presents a variable neighborhood search (VNS) optimization algorithm for the design of the parameters of supplementary damping controllers: power system stabilizers (PSS) and the interline power flow controller–power oscillation damping (IPFC–POD) set. The objective is to insert damping to local and inter-area oscillation modes in multimachine power systems. The electric power system dynamics is represented by the current sensitivity model. Simulations were carried out using three systems: a test system known as Two-Area Symmetrical and two real systems, the New England and the Reduced Southern Brazilian. The VNS method was compared with a multi-start algorithm in terms of performance, showing better convergence rates. The proposal was also able to obtain solutions with high damping levels, that showed to be robust when changes on the operating point of the power system were considered. Finally, it has been verified that the PSS controllers were effective for damping the local mode oscillations, while the IPFC–POD set operated mainly damping the inter-area modes. [ABSTRACT FROM AUTHOR]

The aim of PMU placement in power system is to provide network observability. Usually, the PMU placement is done assuming simple bus arrangement for all the network buses. Therefore, it does not guarantee the observability of complex buses under operational arrangements in which the lines at complex buses are not connected to each other at an individual busbar. In this paper, a new formulation for PMU placement is developed based on ILP that considers the necessity of the network observability under all possible arrangements of lines connections at complex buses. Moreover, in order to prevent the installation of PMU for observability under arrangements that are possible but are not actually probable, a probabilistic PMU placement is presented that considers only the probable configurations, each weighted by its probability. In this case, the lines outage and PMUs failure probability are also taken into account. The simulation results indicate the performance of the presented method to solve PMU placement problem in the presence of complex buses and show that more number of PMUs are required in a network with complex buses. [ABSTRACT FROM AUTHOR]

With wide applications of power electronic devices in modern power systems, simulation using traditional electromechanical and electromagnetic tools suffers low speed and imprecision. Multi-rate methods can enhance efficiency of simulation by decreasing the scale of systems in small time-steps. However, the existing traditional methods for multi-rate simulation suffer the problems of instability and simulation errors. These have hindered the application of multi-rate simulation in power industry. Therefore theoretical evaluation on different multi-rate simulation methods is crucial to understand the feasibility and limitation of the methods, and to contribute to overcome the drawbacks of the traditional methods. In this paper, the multi-rate simulation performance based on two traditional technologies and a Modified Thevenin Interface are evaluated to provide an overall feasibility of multi-rate algorithms in the power simulation. The Modified Thevenin Interface is proposed to overcome the drawbacks in synchronization. Three theorems are proposed and proved for theoretically analyzing the stability of the simulation methods. Error analyses of the multi-rate methods are performed to identify the relationships between errors and simulation conditions. Besides, the accuracy and efficiency performance in a practical project of VSC-MTDC shows the feasibility and necessity by using multi-rate simulation. Through the theoretical analysis, the issues of stability and accuracy of multi-rate simulation for the DC grids have been better understood, based on which an improved simulation algorithm has been proposed to overcome these issues. Long-term system dynamics of large-scale systems containing DC grids and fast transients of HVDC converters can be investigated simultaneously with high speed and sufficient accuracy. [ABSTRACT FROM AUTHOR]

Owing to mal-operation of the conventional scheme during high resistance ground fault near tap point, a new faulty section identification and fault localization technique for three-terminal transmission line is presented in this paper. The proposed technique utilizes time-synchronized voltage and current signals from all the three terminals. Initially, fault detection based on estimation of superimposed voltage of tap point with reference to all three terminals has been carried out. Subsequently, utilizing the above three estimated superimposed voltages; faulty section identification criterion is formed. Finally, fault localization i.e. estimation of the value of fault distance and resistance has been performed. The authenticity of the proposed technique has been verified by simulating an existing 400 kV Indian three-terminal transmission network in PSCAD/EMTDC software. The simulation results point out that the proposed technique is able to identify the faulty section correctly. Moreover, it precisely estimates the value of fault distance and fault resistance as the percentage error for fault location and resistance remains within ±1.5% and ±3.5%, respectively. Likewise, its performance remains unaffected during wide variation in fault and system parameters. At the end, comparative evaluation of the proposed technique with the existing protection scheme clearly shows its superiority. [ABSTRACT FROM AUTHOR]

This paper presents an efficient protection method which can be used for both meshed and radial distribution networks (DNs) with synchronous-based distributed generation (SBDG) units. The method does not require any communication system in the both grid-connected and islanded modes of operation. The microprocessor-based relays used in the DNs are programmed with a new time-current-voltage characteristic utilising only local fault voltage and current magnitudes. The proposed method is verified by simulation study on the DN of IEEE 30-bus test system as a meshed network in grid-connected mode. The method is also tested on an Iranian practical radial DN in the both grid-connected and islanded modes of operation. The test cases include different fault conditions, with SBDG at various locations and different DG penetration levels, and also without any SBDG in the networks. It is shown in a comparative study that the new time-current-voltage characteristic achieves a notable reduction in total relay operating times without any communication links. In addition, the method uses the same protection settings for the both grid-connected and islanded modes of operation. [ABSTRACT FROM AUTHOR]

Considering travelling wave’s bandwidth which varies from several kilohertz to hundreds of kilohertz, traditional current and voltage transformers cannot transfer whole bandwidth of travelling wave. However, electronic transformers, including Rogowski coil based electronic current transformer and capacitance divided electronic voltage transformer, have much wider bandwidth (up to 500 kHz) which could transfer almost whole bandwidth of travelling wave without distortion. Besides, secondary side’s output of electronic transformer is the differential signal of primary side. So, the integration circuit can be omitted when using differential travelling wave signal directly in protection principle. Traditional travelling protection for high voltage direct current (HVDC) lines is highly affected by grounding resistance. And the backup protection, such as current differential protection, has long operation time. So the paper proposes a novel travelling wave pilot protection based on the differential output signal of electronic transformers. Differential voltage and current travelling wave have axisymmetric relationship when the fault occurs at forward direction. Conversely, differential voltage and current travelling wave almost overlap when the fault occurs at reverse direction. Considering fault direction identification results of two ends, fault section can be determined. Besides, according to amplitude ratio of fault line and normal line, fault line can be selected correctly. The simulation results in PSCAD/EMTDC prove the correctness, sensitivity and reliability. [ABSTRACT FROM AUTHOR]

Fault location is a necessity to realize the self-healing concept of modern distribution networks. This paper presents a novel fault location method for distribution networks with distributed generation (DG) using measurements recorded at the main substation and at the DG terminals. The proposed method is based on an iterative load flow algorithm, which considers the synchronization angle as an unknown variable to be estimated. Therefore, it obviates the need of synchronized measurements. A new fault location equation is also proposed which is valid for all different fault types, hence the fault type information is not required. The developed method can be simply implemented by minor modifications in any distribution load flow algorithm and it is applicable to different distribution network configurations. The accuracy of the method is verified by simulation studies on a practical 98-node test feeder with several DG units. [ABSTRACT FROM AUTHOR]

In this paper, we investigate optimal locations and capacity for integrating storage systems in the electric transmission grid to improve wind power production. The impacts on wind power production and conventional thermal generation due to operation of utility-scale storage systems are simulated. A compressed air energy storage (CAES) is chosen as an utility-scale storage technology, which can provide several hundred MWs of electric power. A mixed integer programming (MIP) is implemented for the mathematical formulation. The Electric Reliability Council of Texas (ERCOT) wind, load data and its simplified transmission system are used for a case study. To mandate wind power production, we apply 20% goal for renewable portfolio standard (RPS). Operation of 1350 MW CAESs improves wind power production and RPS target achievements, however, thermal generation does not significantly decrease under the given simulation condition. [ABSTRACT FROM AUTHOR]

This paper presents a novel method for the power transformer insulation coordination, based on the risk of failure analysis due to lightning surges, that uses its insulation strength volt–time curve and a limit–state surface formulation. The limit–state surface is derived in a novel way, from the optimal number of systematic numerical simulations of transformer terminal overvoltages—emanating from station impinging lightning surges—while accounting for the transformer insulation volt–time curve and surge arresters protective characteristics and disposition. The proposed method further employs a state-of-the-art transmission line (TL) and substation equipment models for lightning-surge transient analysis, constructed in the EMTP software package. It also uses the electrogeometric model of lightning attachment to TLs, in order to estimate the expected number of direct lightning strikes, along with a bivariate statistical distribution of lightning currents. The main aspects of the proposed method are demonstrated by means of the computational example featuring an air-insulated substation power transformer lightning insulation coordination. Simulation results exhibit many benefits of the proposed method. Sensitivity analysis further reveals different influences that the various model parameters have on the transformer insulation coordination design. [ABSTRACT FROM AUTHOR]