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Protecting DC microgrids (DCMGs) from faults is critical due to the rapid current changes that occur in milliseconds. However, ensuring fast and accurate protection in DCMGs is more challenging than in AC systems. This study proposes a novel protection algorithm using traveling waves (TWs) for fault detection and localization. The high‐order synchrosqueezing transform (FSSTH) is applied to precisely identify TWs at the relay location. FSSTH offers a sharp time–frequency representation, enhancing the accuracy and speed of fault detection. This method can accurately detect transient phenomena like TWs in DCMGs, even with noise and variable fault resistance. By using the spectral envelope with FSSTH, ridges in time–frequency representations are extracted, improving fault diagnosis. The approach differentiates external from internal faults and recognizes fault direction by assessing TW polarity. Testing on two different DCMGs showed this algorithm's high efficiency and accuracy, with fault location errors ranging from 1 to 50 meters in low‐voltage and 13 to 64 meters in medium‐voltage DCMGs, even under challenging conditions like high resistance (up to 500 Ω) and low signal‐to‐noise ratio (5 dB). These results demonstrate the method's superior accuracy and robustness compared to existing techniques. [ABSTRACT FROM AUTHOR]

Fast progress of High Voltage Direct Current (HVDC) technology has been considerable over the past decades. Emerging Modular Multilevel Converter (MMC) provides power systems with promising solutions to integrate large‐scale renewable energy sources, as well as multiple asynchronous power grids. Consequently, implementation of a multi‐terminal HVDC transmission system has been easier using MMC converters. However, protection of multi‐terminal MMC‐based HVDC grids under DC fault conditions is a challenge for the industry. This study sheds light on concept of system‐level DC protection coordination for multi‐terminal HVDC grids. Although, there are different protection methods for HVDC transmission systems including multi‐terminal ones, there are no well‐defined protection coordination strategies for transmission links protection and belonging HVDC converters under DC fault conditions. The proposed protection coordination prevents unnecessary tripping of MMCs in the multi‐area HVDC grids and supports the system with minimum effect on healthy parts. For the first time, different HVDC Converter Tripping (HCT) profiles are presented based on a fully selective protection strategy and their characteristics are discussed comprehensively. Simulation results demonstrate the effectiveness of the proposed strategy for multi‐terminal MMC‐based HVDC grids. The proposed coordination can be applied to DC grid code requirements of meshed HVDC grids in the future. [ABSTRACT FROM AUTHOR]

The protection of traditional high‐voltage capacitor banks relies on an unbalance relay which operates when an internal fuse is blown. However, the unbalance relay cannot indicate the cause of the fault. Thus, an operator wastes time and human resources investigating the fault issues. In this paper, a fault which occurred in a 230‐kV power system of Electricity Generating Authority of Thailand was observed by performing simulations using the Power Systems Computer Aided Design (PSCAD) program. The study system based on the double bus station and 72 MVAR capacitor banks was installed in the form of a back‐to‐back topology. Three scenarios were considered: normal condition, fault occurrence in one capacitor bank and fault occurrence in both capacitor banks. Current characteristics such as the current phase and difference in unbalance current were considered. In addition, discrete wavelet transform was applied to solve the ambiguity of current generated from the PSCAD. The authors' results suggest that identifying fault events using a coefficient of wavelet is more efficient than relying on the current amplitude. The findings mentioned in this paper can be applied in a traditional power system protection scheme to enhance a system's reliability. [ABSTRACT FROM AUTHOR]

Modular multi‐level converters (MMCs) are a mainstay in many HVDC transmission projects worldwide. Half‐bridge MMC (HB‐MMC) is mostly used in the current project. The large capacitor of sub modules (SMs) is often required in MMC to ensure the low voltage ripple. Here, the three‐stage switching MMC (TSS‐MMC) topology is proposed, which can greatly reduce the capacitor voltage ripple of SMs by dynamically adjusting the position of inductance on the upper and down bridge arms. The principle of reducing capacitor voltage ripple based on equal capacitance theory is introduced. The selection of the inductance value of each part in TSS‐MMC is introduced. The start‐up process strategy, capacitor voltage ripple reduction strategy in steady‐state operation, and DC fault ride‐through strategy of TSS‐MMC are proposed. The effectiveness and engineering practicability of the proposed TSS‐MMC is verified by transient simulation program built on PSCAD/EMTDC. The simulation results show that compared with MMC with circulating current suppressing controller (CCSC), it can effectively reduce the capacitor voltage ripple by over 50%. Furthermore, the total used inductance of TSS‐MMC can also be reduced. A comprehensive assessment of TSS‐MMC is also carried out. [ABSTRACT FROM AUTHOR]

Even though shunt compensation of transmission lines (TLs) is a common practice to limit the overvoltages stemming from the Ferranti effect, it may cause transient and steady‐state resonant overvoltages when one phase is left open due to the single‐pole‐open condition following the temporary phase‐to‐ground (Ph‐g) fault. Furthermore, the existing shunt reactors potentially increase the duration of the secondary arc current at the fault point and hence prevent offering fast single‐pole reclosing. To exploit the mentioned issues, in recent studies, a neutral reactor is introduced, which is installed in the neutral point of the shunt reactors; nonetheless, obtaining the appropriate amount of it is remarkably challenging. In this paper, an optimal neutral reactor (ONR) is determined based on an optimization problem, which minimizes the neutral reactor cost subject to limiting both resonant overvoltages and the duration of the secondary arc current. In modelling, the Laplace domain is employed rather than the phasor domain to consider both transient and steady‐state conditions since this technique allows having better control over transient overvoltages as well as transient secondary arc. [ABSTRACT FROM AUTHOR]

As the distributed energy resources penetration level increases, the distribution system operator faces a challenging task of unintentional islanding detection. Besides islanding detection schemes are affected due to the presence of different types of distributed generation systems and smart inverters. The presence of these devices hinders the capability of islanding detection schemes. To mitigate these issues, this study proposes a practical methodology of variational mode decomposition‐based energy index for islanding detection. It decomposes the sampled voltage signal at the point of common coupling into four modes/intrinsic mode functions (IMFs). Among these modes/IMFs, the energy index of mode two has been utilised to detect the islanding. It is an entirely intrinsic, adaptive, and variational method. The five bus and practical distribution systems have been modelled using PSCAD/EMTDC software while considering various components' practical aspects. The technique has been tested for the mixed type of distributed generation and various transient events. The test results reveal that the proposed method is capable of discriminating the islanding event from other disturbances. [ABSTRACT FROM AUTHOR]

The large‐scale wind energy conversion systems (WECSs) based on doubly‐fed induction generators (DFIGs) are very popular in recent years due to the numerous technical and economic benefits. With the increasing penetration level of wind energy, the latest grid codes require the DFIG‐based WECSs to remain connected to the grid under grid fault scenarios and deliver the required reactive power into the grid. However, the direct connection of the stator of the DFIG to the grid makes it prone to grid disturbances, especially to voltage sag. This study proposes a modified demagnetisation control strategy to enhance the low‐voltage ride‐through (LVRT) capability of the DFIG under grid faults. The proposed control strategy is implemented in a coordinated approach by using the existing demagnetisation control and the addition of an external resistance in the stator side of the DFIG. The demagnetisation control damps the direct current component of the stator flux and the external resistance accelerates the damping of the transient flux by decreasing the time constant and hence, enhancing the LVRT capability of DFIG. The effectiveness of the proposed control strategy is demonstrated under both symmetrical and asymmetrical grid faults simulated system through MATLAB/Simulink®. The comparative results justify the merits of the proposed methodology. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive control strategy to improve the transient response of a stressed power system apparatus. This strategy, based on the set point automatic adjustment with correction‐enabled (SPAACE), is an auxiliary control method to enhance the set point tracking of an apparatus. SPAACE modifies the set point of the controllable apparatus using a feedback signal from its output to mitigate transients that can be caused by events such as faults, load variations, and large reference set point changes. In this work, an adaptive version of SPAACE (ASPAACE), which uses an adaptive dead‐zone band, adaptive scaling factor, and exponential prediction is introduced. Moreover, this study investigates the relationship between the natural frequency of the system and the prediction horizon of the ASPAACE controller. To demonstrate the performance of ASPAACE, different case studies are presented. [ABSTRACT FROM AUTHOR]

The high‐resistance faults at the far end are the most important factor that causes protection failure of HVDC transmission lines. In the initial stage of the transmission lines fault, the transient information of power grid is abundant, and the sequential overlapping derivative (SOD) transform can emphasise the characteristics of the high‐frequency transient signal and its sudden change direction, amplify fault characteristics, and eliminate noise as far as possible, which is of great benefit to identify the high‐resistance faults at the far end. A fault identification method based on the SOD transform of voltage transient is proposed. In this method, the initial fault voltage travelling wave is processed by the SOD transform, and the initial fault voltage is a travelling wave is quickly detected. The set value of SOD transform is obtained according to the traversal simulation fault location, thus the identification criteria of internal and external faults are obtained. The simulation results show that the method can accurately identify the high‐resistance faults at the far end, and it is hardly affected by transition resistance and fault distance. [ABSTRACT FROM AUTHOR]

Due to the progressive penetration and usage of renewable sources and loads based on power electronics, medium voltage direct current (MVDC) distribution system is getting broad attention. Direct current circuit breakers (DCCBs) are of vital importance for the reliability and flexibility of power system. With features of low cost and micro‐operating losses, multi‐port hybrid DCCB with negative voltage source (NVS) has been proposed by the authors and might be a better choice. To further promote its industry application in MVDC system, interaction characteristics between DCCB and power system are investigated in this study. The structure of multi‐port hybrid DCCB is briefly introduced. Then, considering the diversified working conditions, e.g. single fault, multiple faults and switching load current with random direction, the cooperation sequence of components in multi‐port DCCB under all these working conditions is proposed, respectively. Then, based on simulation model established in PSCAD/EMTDC, transient current/voltage distribution pattern inside multi‐port DCCB and its mechanism are discussed, and simulation results have verified the superiority and effectiveness of multi‐port hybrid DCCB with NVS in MVDC system. [ABSTRACT FROM AUTHOR]

This study presents a novel multi-rate algorithm for the co-simulation of power system transients using base-frequency dynamic phasor solver for frequency adaptive simulation of transient (BFAST) and electromagnetic transient (EMT) solvers. The BFAST solver alters its solution technique from dynamic phasors to EMT based upon the frequency contents of the waveforms being simulated. A changeover algorithm between the two solvers is also presented. The BFAST solver is then integrated with an industrial-grade EMT solver to develop a BFAST–EMT multi-rate co-simulator. The interface between the two solvers is established using transmission lines at the partitioning locations. The co-simulator combines the benefits of dynamic phasors, frequency adaptive simulation of transients, parallel processing, and multi-rate simulation. The study describes the several solution modes of the proposed co-simulator. Illustrative examples are included to demonstrate the accuracy and computational benefits of the proposed co-simulator. [ABSTRACT FROM AUTHOR]

This study proposes an alternative method to calculate the transient responses of multi‐conductor overhead transmission lines based on ABCD representation, recursive convolutions and numerical method for rational approximation in the frequency‐dependent curves. In the classical universal line model, the characteristic admittance matrix Yc(ω) and propagation matrix H(ω) are represented by rational functions. In H(ω), previous and correct identification of the modal travelling times is required. However, these modal travelling times are estimated numerically, which do not offer good accuracy in some cases. This fact has a considerable effect on the rational representation of H(ω) itself and consequently on the transient responses. In the alternative method, a previous estimation of the modal travel times is unnecessary because when using the ABCD representation for each propagation mode, a direct relation exists between the currents and tensions of the receiving and sending ends. These relationships are fitted by smooth rational functions, and then, using recursive convolution methods, the authors obtain the explicit equations of the currents and voltages to calculate the transient responses. The results demonstrate that the alternative method is accurate when compared with the frequency‐domain solution of the transmission line transformed to the time domain using the numeric Laplace transform and with the Bergeron method. [ABSTRACT FROM AUTHOR]

In this study, an advanced phase‐locked‐loop (PLL), which has a simple structure and a low computational burden is proposed. The proposed PLL also improves the dynamic performance and the filtering capability of the conventional three‐phase enhanced‐PLL (3pEPLL) significantly. The conventional 3pEPLL operates three individual EPLL blocks for each phase voltage and a fourth EPLL for estimation of the magnitude, frequency, and phase angle, which considerably increases the structural complexity and computational burden. However, the proposed PLL called enhanced‐3pEPLL (E2 PLL) employs only two single‐phase EPLL modules in its pre‐filtering stage. A moving‐average‐filter (MAF) is also supplemented on the error signal path of these EPLL modules, which allows smoother estimation of the magnitude, frequency, and phase angle, and improves the filtering capability of the EPLLs. Unlike the conventional 3pEPLL, the proposed E2 PLL employs a quasi‐type‐1 PLL (QT1‐PLL) to estimate the magnitude, frequency, and phase information of the fundamental grid voltage. The structure of QT1‐PLL is similar to a type‐1 PLL, which offers a low transient response time. The small‐signal model of the proposed PLL is derived for stability analysis and parameter design procedure. The effectiveness of the E2 PLL is verified owing to experimental results and comparison with the conventional 3pEPLL and QT1‐PLL. [ABSTRACT FROM AUTHOR]

The essence of the mathematical model of disconnectors' multiple reignition arc is the repeated breakdowns of SF6. In this study, the kinetic properties of microparticles are studies based on the streamer discharge theory, and a fluid arc mathematical model applied in centimetre clearance is established. Ultra‐High Voltage (UHV[AQ ID=Q1]) disconnector manufactured by Pingao Electric Co. Ltd of Henan Province is selected as the object and the resistance change process of contact clearance multiple reignition arc is simulated by finite difference method‐finite element method‐flux corrected transport self‐programming in MATLAB based on the chamber structure and operating characteristics. UHV gas‐insulated switchgear very fast transient overvoltage (VFTO) test platform is built to gain the characteristics of VFTO waveforms generated by the disconnector's operation. Compared with simulation results, the test data shows that the fluid arc mathematical model can scientifically explain the dynamic development process of microparticles in the contact clearance and the calculation results are consistent with the test data. In addition, the arc fluid mathematical model combines the structure and operating characteristics of the switch with the development process of microparticles, which can better guide the design of the switch, and provide a theoretical basis for the suppression of VFTO with the disconnector itself. [ABSTRACT FROM AUTHOR]

Multiterminal high‐voltage direct current (HVDC) systems still need advances in terms of protection in order to improve their reliability. In this context, the distance protection can play a major role by adding selectivity to the existing DC fault detection algorithms. Hence, the present work proposes a non‐unit DC distance protection algorithm that uses the frequency of the DC voltage transient oscillation to estimate the distance of the fault. The DC voltage transient frequency is extracted using the Hilbert–Huang transform and compared with a pre‐defined frequency/distance curve. The technique was evaluated by simulating faults in a four‐terminal symmetric monopole multiterminal HVDC system. In the simulation environment the algorithm was fully selective for faults within the first protection zone and had a correct operation rate of 94% or more for faults located in the second protection zone. To further validate the presented technique, the proposed algorithm was embedded in a digital signal controller, running in real‐time. In all performed tests in hardware, the faults were correctly detected and identified as being internal or external. The results indicate that the proposed algorithm could be used in real‐world applications, in conjunction with fault detection techniques, adding selectivity to multiterminal DC protection schemes. [ABSTRACT FROM AUTHOR]

Currently, an issue of relay protection (RP) settings determination that ensures its correct operation in electric power systems (EPSs) has not been resolved completely. The main reason for this is the lack of methods and tools for adequate consideration of transients during a fault existence for RP settings calculation. In this study, a novel approach for RP settings determination is presented. Its main feature is the application of detailed mathematical models reproducing simultaneously processes in the entire set of elements in the RP scheme, including instrumental transformers, and in large‐scale EPS mathematical model as a whole. This key feature can be achieved via the hybrid power system simulator – hybrid real‐time power system simulator – implementing a methodically accurate analogue–digital solution of the EPS mathematical model. The numerical transformer differential protection (NTDP) based on this approach was set up via the standard dual‐slope tripping characteristic. Also, a novel approach to the formation of the tripping characteristic is proposed. The key feature of this approach is applying a flexible curve that enveloping all fault characteristics Idiff = f (Irest) of those modes in which the NTDP should not trip. [ABSTRACT FROM AUTHOR]

For low‐voltage autonomous microgrids, the essential goal is maintaining stable voltage and frequency throughout its network for the smooth operation of distributed loads. The other goal is to maintain proportionate power‐sharing between multiple sources connected through voltage source converters (VSCs). For the particular case of a heavily loaded microgrid, any further increase in demand poses new problems. The VSCs proximate to the loads may overshoot beyond its maximum ratings. Owing to which the stability of the power supply, as well as the longevity of VSCs, may get compromised. Also, these sources provide power under varying composite loading conditions comprising both linear and non‐linear loads resulting in unbalancing in its network. To overcome these problems, a decentralised fast terminal sliding mode control strategy for active power‐sharing between parallel VSCs has been proposed. A detailed mathematical model based on Lyapunov's stability theory‐based study is designed to establish the operating stability of the proposed controller. To validate the proposed control strategy, MATLAB‐based simulation results are provided for possible loading scenarios. A comparative study for performance evaluation between the proposed controller and a conventional proportional ‐integral‐based controller is further carried out. Finally, the performance of the proposed controller is also validated in real‐time scenario. [ABSTRACT FROM AUTHOR]

Transient voltages from (dis)connecting compensation coils near high voltage transformers are studied. Non‐invasive sensors are needed in order to exclude any influence by the measurement equipment on the overvoltage magnitude. This study describes results from open‐air capacitive sensors as part of a differentiating/integrating measurement system. Its bandwidth (up to 10MHz) allows to record large detail in the switching events. However, the coupling strengths and the cross‐couplings inherent to the use of air capacitive sensors need to be determined. Calibration based on symmetric phase voltages during normal operation supplies part of the information. Three methods are compared to supplement this knowledge for establishing the complete coupling matrix between phase conductors and sensors. One method employs estimates from the system configuration, in particular, its symmetry. The other techniques extract information from fast transient events within the responses for both switching on and off. The decoupled waveforms from different methodologies align within their confidence bounds and predict the maximum overvoltage magnitudes within an accuracy of 5% when employing information from the fast transients. Based on measurements performed on two compensation coils, both tested three times, larger overvoltages occurred during energisation compared to de‐energisation with maximum amplitude exceeding three per unit. [ABSTRACT FROM AUTHOR]

This study presents a multi‐scale transient model of cascaded H‐bridge (CHB) converter for distribution network‐interactive studies, which is capable of simulating slow‐changing dynamics up to high‐frequency switching transients. The switching pulse behaviours of H‐bridges are described using the waveform propagation theory. By taking individual H‐bridge sub‐modules into account, a semi‐analytic function (SAF) model of the CHB multilevel converter is developed. It allows for accelerated simulation of switch‐type electromagnetic transients (EMTs). During slow‐changing dynamics, the developed SAF is converted to a shifted‐frequency phasor (SFP) model using the Fourier series expansion. Due to the consistent modulation and complex analytical signal processes, smooth transitions between the SAF and SFP are achieved for different running stages. Moreover, the proposed model is readily integrated with external multi‐scale models of the distribution network. The validity of the proposed multi‐scale model is performed through case studies that include the CHB internal fault, distribution network faults, and also interactive dynamics between them. The accuracy and efficiency of the multi‐scale model is verified through comparisons of the results with those obtained from the full EMT‐type programmes. [ABSTRACT FROM AUTHOR]

As a modular multilevel converter‐based medium‐voltage direct current (MMC‐MVDC) distribution grid mostly utilises small current grounding modes, the weak fault current for single‐pole‐to‐ground (SPTG) fault is very difficult to detect especially in the case of noises and fault resistance. Therefore, this study proposes a fast and accurate faulty feeder selection and segment location method. For SPTG fault, the transient current fault component is the charge–discharge current of distributed capacitance on the DC feeder. Analysis indicates that the waveforms of current fault component of positive and negative poles are negatively correlated for a faulty feeder; while they are positively correlated for a non‐faulty feeder. According to these characteristics, a faulty feeder selection criterion using Pearson correlation coefficient (PCC) is constructed. Then, utilising the energies difference between the current fault components of two poles, the faulty pole can be verified. In addition, the faulty segment is located by the PCC of the current fault component on both sides of each segment. Finally, simulation results confirm the validity of the proposed faulty feeder selection and segment location method. [ABSTRACT FROM AUTHOR]

Any incorrect action by the distance relay is harmful to the stability of power system at a power swing condition. In this respect, discrimination of faults from power swing should be fast and accurate. This paper introduces a new fault detection method using time derivative of voltage signals at swing condition. The sample interval between two successive peaks of the derivative of a voltage signal always remains above a minimum value during power swing, while its value decreases by a significant margin after the occurrence of a fault. This discriminating feature of the differential voltage is mathematically developed and applied to detect faults under swing conditions. A 9‐bus‐modified WSCC system is considered for validating the method, and the simulation is carried out in an electromagnetic transient programme. The method detects both symmetrical and unsymmetrical faults accurately and quickly at power swing condition for various fault locations, power angles, fault inception times, fault resistances and swing frequencies. Its performance is satisfactory for series compensated lines and under noisy condition. The fault detection results and the comparative study with two available methods justify its potential. [ABSTRACT FROM AUTHOR]

Electric transient events are recurrent phenomena in electrical installations and distribution systems or grids; hence, the identification of these kinds of phenomena has become an important topic for researchers. This work presents a methodology to identify and accurately delimit transients in current signals of non‐residential buildings. The proposed method firstly analyses the signal using the wavelet transform to pre‐visualise the transients, and then opening and closing morphological operators are applied to the signal to find the beginning and ending of the transient; furthermore, the highest point of the transient and its location is obtained. The experimentation is performed with real current signals measured in a non‐residential building. The results indicate that the proposed method can precisely identify and delimit transients, even when the transients are very close to each other. [ABSTRACT FROM AUTHOR]

This study proposes an adaptive boosting (AdaBoost) algorithm for precise and accurate prediction of transient security assessment of power systems using synchronised measurements. The proposed approach (PRPA) also determines the generator coherent state as well as the synchronism status of each generating unit. The PRPA consists of three classifier models, in which classifier I determines the transient security status and classifier II is used to determine the generator coherency. Classifier III is a hybrid classifier, which determines the individual generator synchronism state for a given operating condition. This hybrid classifier consists of an array of parallel classifiers, where one classifier is assigned to each generating unit of the power system. For this assessment, the measured rotor angles of the generators are used as inputs to the proposed classifier models. In classification stage, several weak classifiers are combined in a linear manner to construct a strong classifier. The performance of the AdaBoost algorithm is further improved by a new weight updation strategy using fuzzy clustering thresholding technique. Simulation results obtained from IEEE 14‐bus, IEEE 30‐bus and Indian 246‐bus systems reveal that the PRPA can enhance the overall monitoring and assessment of power system using synchronised measurements. [ABSTRACT FROM AUTHOR]

The authors use a TMS320 digital signal processor (TMS320‐DSP) to determine fault instants and estimate their location in real time in a laboratory environment. The fault instant is determined via examining the instantaneous differential changes in the line currents. After the fault is detected, the fault location is determined by processing the time‐domain transient current waves. First, the travelling‐wave frequency is determined by application of the fast Fourier transform to the positive‐sequence‐component line current after the fault, and subsequently, the fault location is estimated by utilising this frequency. The alternative transients programme (ATP)–electromagnetic transient programme is used to simulate the line currents and create short‐circuit fault conditions. Furthermore, LabVIEW software and a National Instruments data acquisition board are used to transform the line currents obtained through the ATP programme into analogue signals. The TMS320‐DSP determines the fault in real time and estimates the fault location using the completed software and analogue input signals. Their results indicate that the prototype device designed with the use of the TMS320‐DSP is suitable for real‐time fault detection. [ABSTRACT FROM AUTHOR]

In order to solve the problem of noise interference in power quality disturbance identification, a new method of multiresolution hyperbolic S‐transform for noise abatement based on energy density is proposed. First, multiresolution hyperbolic S‐transform is performed on the power quality disturbance signal. This method combines suitable time‐frequency resolution with good noise suppression performances. Second, the transient disturbance time‐frequency domain is determined according to the fluctuation energy density. By using a mean time‐frequency filter, the interference of the noise in the non‐transient disturbance time‐frequency domain with signals is eliminated, and the noise in the non‐signal time‐frequency domain is suppressed. Then, the signal time‐frequency domain is determined according to the energy density, and the noise in the non‐signal time‐frequency domain is further suppressed by the denoising time‐frequency filter. The characteristic curve is extracted from the complex matrix module after the noise abatement. Finally, a time‐frequency database of tree structure is established. The dynamic time warping distance query classification method is used for quick classification according to the relationship of membership degree, which reduces the number of queries and improves the recognition accuracy. The classification result shows the effectiveness of the algorithm in high noise background and the applicability in actual fields. [ABSTRACT FROM AUTHOR]

Several international standards have suggested to detect the unintentional island formation to safeguard the working personnel and protect the electrical equipment in the system. An active islanding detection technique, which employs the q‐axis current disturbance injection, has been utilised and an analysing technique is proposed in this work based on a combination of band pass filter and mean of absolute frequency variation (AFVmean) to detect and differentiate the island formation from other transient events. The proposed analysing technique (PAT) detects island formation within 180 ms, which is less than the prescribed time of various international standards, applicable to dynamic loading conditions without the need of adaptive threshold and communication, and offers zero non‐detection zone (NDZ). The disturbance injection makes significant variation in the frequency of voltage signal on post‐islanding condition even for zero‐power mismatch condition, therefore, the NDZ is zero. The PAT is corroborated for various islanding and non‐islanding events and the simulations are performed in MATLAB/Simulink tool. [ABSTRACT FROM AUTHOR]

The results of an electromechanical transient simulation can be viewed as a time series data set. Storing these data requires a sizeable space, and the considerable data size renders comparative analysis difficult. For mitigating these problems, a method for analysing and describing a discrete‐event chain in the dynamic process of a power system is proposed. Based on the symbolic description, the continuous dynamic process is represented as a discrete‐event chain, resulting from the change in state variables beyond the given threshold. Therefore, the event‐driven electromechanical transient simulation is developed, and the continuous dynamics and discrete‐event chain simulation results are obtained. Subsequently, the event relation matrix is obtained, normalised, and then converted into a bitmap. Finally, the k‐means method is used for the cluster analysis on the bitmap of the simulation result. Two test cases involving an IEEE 39‐bus system and a practical system are considered. Case studies demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In the hierarchically connected ultra-high voltage (UHV) DC projects, the minimum air clearance on the 1000 kV AC side of converter transformer directly affects the layout and area of the valve hall. The minimum air clearance is determined by the overvoltage and the flashover characteristics of different electrodes. Since the UHV DC projects are hierarchically connected to the AC power grid, the overvoltage and the electrode flashover characteristics are different from that of general UHV AC projects, necessitating the relevant overvoltage calculation and test studies. The electromagnetic transients software PSCAD is used for modelling of the ±1100 kV Wannan convertor station and the related AC system. The power frequency overvoltage, switching overvoltage, time-to-crest value, and coefficient α of phase-to-phase overvoltage on the AC side of the 1000 kV converter transformer are calculated. Tests are carried out on air clearances between bundle conductors, tubular buses, and equipment grading rings under switching impulse with 1000 μs long wave-front. The minimum phase-to-earth and phase-to-phase air clearances on the 1000 kV AC side of the converter transformer are given. [ABSTRACT FROM AUTHOR]

The accessing of distributed generation resources to distribution network leads to a multi power grid structure. The direction of power flow changes with it. The photovoltaic (PV) generation contains a large number of power electronic devices and control links, which causes that the output responses and fault characteristics are significantly different from the synchronous machine. In consideration of the topological structure of the distributed distribution network, this paper analyses the differences of transient characteristics of AC distribution line with PV power supply between internal and external faults. Then, a new principle for constructing directional element using transfer and consumption characteristics of high-frequency transient energy is proposed. This directional element only uses high-frequency transient fault voltage and current in early stage, which can reliably distinguish the fault direction. What's more, the existence of transition resistance will be conducive to the judgement. Finally, corresponding simulation cases were carried out to verify the feasibility and superiority of the proposed directional element. [ABSTRACT FROM AUTHOR]

As a most widely applied real-time digital simulation system, real time digital simulation (RTDS) is however quite limited on scale of simulation by the number of hardware purchased. Through frequency-dependent network equivalent (FDNE), scale of simulation of RTDS could be largely increased by frequency equivalent on limited hardware. Based on basic principles of FDNE, function limitations and problem are analysed, taking the Shanghai Sijing district power grid as an example; detailed simulation model and FDNE equivalent module are built, transient characteristics under faults before and after FDNE equivalent are analysed. Furthermore, the fault characteristics of high-voltage direct current (HVDC)-Sijing power grid is also studied, which provides a realistic means for real-time digital simulation of AC–HVDC hybrid power grid with limited hardware of RTDS. [ABSTRACT FROM AUTHOR]

Due to the fast development of UHVDC, the power transferring through HVDCs takes a great part of the power from West China to East China. The response for multiple-coupled HVDCs can only be simulated through EMT programmes. To increase the simulation accuracy, the EMT-TS Hybrid simulation has been used in studies of the power system operation. Currently, the EMT-TS hybrid simulation speed is too slow to be unaffordable. This paper presents a novel power system tearing technology to greatly improve the simulation speed in EMT-ST Hybrid Simulation. The TS network is teared according to obtain network islands as many as possible, while the EMT network is teared through the combined transmission line and electric nodes. An algorithm is supposed to form the EMT-ST sub-network groups, which has no coupling with each other. Then, a novel parallel programme structure is proposed to use this EMT-ST sub-network groups to realise the parallel simulation and speedup the simulation. The case studies of the grids with seven HVDCs and 3000 nodes show that the proposed method could greatly improve the simulation speed without lowering precision. [ABSTRACT FROM AUTHOR]

The distance protection method with parameter identification can distinguish internal fault from external fault correctly and avoid the transient overreach effectively based on the accurate secondary signal data. However, due to the limitation of the frequency band of the electromagnetic transformer, the secondary signal distortion is caused when the transient signal is transmitted, which limits the application of the parameter identification principle. Here, a matching method of line model and transformer type for relay protection is proposed. Analysed the appropriate frequency band of line model and transformer linear transfer frequency band and the electrical signal beyond their intersection should be filtered out. The simulation results show that this method improves the accuracy of the operation. This method not only makes sense to the practical application of distance protection based on the principle of parameter identification, but also has some reference value to other engineering applications. [ABSTRACT FROM AUTHOR]

Switching AC filter may cause harmonic impact, which may lead to commutation failure of HVDC system. Here, the commutation failure mechanism of HVDC system caused by AC filter switching is studied. The circuit and mathematical model of the transient process simulation of filter switching are established, and the time-domain solution of the overvoltage of each filter including voltage reduction and distortion is given. The commutation failure mechanism of HVDC system is analysed based on the commutation failure analysis method of harmonic voltage and time area. The simulation results verify the effectiveness of the mechanism analysis of commutation failure caused by AC filter switching in HVDC system. [ABSTRACT FROM AUTHOR]

This study proposes a dual-loop supplementary frequency control (SFC) scheme for back-to-back voltage source converter high-voltage DC (BTB-VSC-HVDC) interconnecting asynchronous AC grids, to provide frequency support for each other after a large disturbance. The proposed dual-loop SFC consists of the frequency-active power (f–P) loop and the frequency-reactive power (f–Q) loop. The former deployed on the P-loop of VSC-HVDC can provide frequency support for the disturbed grid during the primary frequency regulation and improve the steady-state characteristics of the frequency response, while the latter attached to the Q-loop of VSC-HVDC supports virtual inertia to ameliorate the transient characteristics of the frequency response. Simulation studies are conducted based on the equivalently simplified model of Southwest Power Grid and Hubei Power Grid interconnected by Chongqing-Hubei BTB-VSC-HVDC. Simulation results show that the proposed SFC scheme can effectively improve the transient and steady-state characteristics of the system frequency response under a wide range of operating condition. [ABSTRACT FROM AUTHOR]

In order to correctly simulate the simultaneous switching of power electronics circuits and to solve the problems of virtual power loss existing in the traditional interpolation algorithm, this article proposes interpolation algorithm considering simultaneous solution and instantaneous solution. After each integration, it searches for the switching events and determines the simultaneous switching. The simultaneous switching events are solved simultaneously. Instantaneous solution is carried out at forced commutation switching instant. The historical terms calculation method in instantaneous solution under different conditions is given, and the exact power loss of forced commutation switch is obtained. After processing all switching events during one time-step, the half-step interpolation is performed to eliminate numerical oscillations. The proposed algorithm is applied to the electromagnetic transient programme of advanced digital power system simulator (ADPSS), and the correctness and effectiveness of the algorithm are verified by simulation tests for typical power electronics circuits. The simulation results show that the proposed algorithm has high simulation accuracy and can satisfy requirements of power electronics simulation. [ABSTRACT FROM AUTHOR]

The traditional electromagnetic transient (EMT) model of transmission line is very slow for the large-scale power systems simulation due to the small step. To accelerate the electro-magnetic transient program (EMTP) calculation, a modified line model used for realising multi-step simulation is proposed. This model is based on the timescale transformation of single-phase coordinate which can transform the primary high-frequency signal into a lower one. By this means, the part which needs to be simulated in detail, such as power electronic devices, can be calculated with a small time step, and a large time step can be used for the other part. In this article, the basic theory of timescale transformation is introduced firstly, and then the new line model is deduced in detail. Finally, a simple system is simulated by the new and traditional model, respectively, and the validity of this approach is verified by comparing with the traditional EMTP simulation. Furthermore, due to the large-step simulation, the calculation speed is improved. [ABSTRACT FROM AUTHOR]

Transient processes at neutral bus of ultra-high value direct current (UHVDC) converter station received insufficient attention, because of the lower amplitude compare to poles. However due to the lower insulation level, electromagnetic transient processes at neutral bus may cause serious fault, and become an important issue that should be studied carefully in the design stage. A method to analyse the electromagnetic transient based on time-domain wide-band circuit simulation is proposed in this study. Models of major equipment are described. The electromagnetic transient of a ±800 kV converter station is calculated. The transient under different operation statuses is compared. Effects of suppression method such as arresters and capacitors are analysed. [ABSTRACT FROM AUTHOR]

According to the actual requirements of the project, when the pole-to-pole fault occurs in the DC system, the fault must be cleared during the capacitor discharge phase, so the requirements of the calculation of the current transient expression at the fault point are made. To solve this problem, this study proposes a dual-port network model with fault flags. First, analyse the equivalent circuit diagram of the tree and ring DC system after fault, and compare it with the dual-port network model. The relationship between the parameters of the original system and the parameters of the proposed model is given. Second, put the relationship expression into the short-circuit current expression of the dual-port network model and obtain the final transient expression for multi-ended systems. Finally, the 3-end tree and ring DC system model are set up on the MATLAB/Simulink software platform. The simulation of the model is verified. The error is below 5%, which proves the reliability of the model. [ABSTRACT FROM AUTHOR]

Islanding detection in distributed generation (DG) interfaced to the microgrid is a key criterion for safety and power quality of the power system. This study proposes a transient monitoring function (TMF)‐based islanding detection technique, which distinguishes between various islanding and non‐islanding conditions in an inverter‐based DG. Initially, the voltage samples of each phase retrieved at the target DG location are processed through Fourier–Taylor transformation (FTT). The TMF is the difference between the estimated voltage samples regenerated from the FTT and the actual sample values. Finally, the TMF index for islanding detection is computed by combining each phase TMF. Based on simulations carried out in PSCAD/EMTDC environment, the performance of the proposed method is examined in various critical conditions. Therefore, the proposed method provides generalised solution irrespective of active and reactive power mismatch and thus enhancing the non‐detection zone. The proposed TMF‐based anti‐islanding relay is highly efficient and satisfies the speed criteria of the relaying function in performing the task. [ABSTRACT FROM AUTHOR]

Due to different fault ride through controls of both the wind farm and the voltage‐source converter high‐voltage alternating current (VSC‐HVDC) converters, the offshore wind farms that are connected to the power system through VSC‐HVDCs have unique fault transients. During a fault on AC side transmission lines, the wind farm and the VSC‐HVDC together provide faulted current, whose amplitude and phase will be decided by their different control strategies collectively. The fault transients are different from those in the traditional AC grid. Thus, the performance of traditional protection will be affected. In this study, the AC fault current expression is deduced, while the influencing factors on the current's amplitude and phase are analysed in detail. Based on these characteristics, the performance of distance relays under the grid side fault of the VSC‐HVDC‐connected offshore wind farm integration system is evaluated. Simulations based on PSCAD have verified the theoretical analysis. [ABSTRACT FROM AUTHOR]

This study presents a method for discriminative detection of direct current (DC) faults on voltage source converter‐powered multi‐terminal high‐voltage direct current transmission systems using two fundamental guiding principles, namely instantaneous current‐differential and travelling waves. The proposed algorithm utilises local voltage and current measurements from all transmission lines connected to a DC busbar, and current measurement from the DC side of the converter. The scheme operates at a sampling frequency of 96 kHz, which conforms with IEC 61869‐9. No long distance communication is involved while measurements and signal exchange within DC substations are enabled by the utilisation of IEC 61850. Performance is assessed firstly through detailed transient simulation, using verified models of modular multi‐level converters, hybrid DC circuit breakers and inductive DC‐line terminations. Furthermore, practical performance and feasibility of the scheme are evaluated through laboratory testing, using the real‐time Opal‐RT hardware prototyping platform. Simulation and experimental results demonstrate that the proposed protection algorithm can effectively, and within a very short period of time (i.e. <1 ms), discriminate between busbar and line faults (internal faults), while remaining stable during external faults. Additionally, it has been demonstrated that IEC 61869‐9 is suitable for enabling fast DC protection schemes incorporating travelling waves. [ABSTRACT FROM AUTHOR]

The increasing interdependence between electric power and natural‐gas systems requires integrated simulation tools applicable to the coupled system. Therefore, this study proposes steady‐state and transient simulation tools for electricity‐gas integrated energy systems (IESs) by using convex optimisation. Steady‐state IES simulation is designed for long‐term planning studies while transient IES simulation, which includes line‐pack storage, is designed for real‐time operational research. The proposed convex steady‐state gas flow model introduces binary variables to represent gas flow directions, and employs the second‐order cone (SOC) to relax non‐convex pipeline gas flow equations. As a result, steady‐state gas flow analysis is formulated as a mixed integer SOC programming problem. The proposed transient gas flow model employs the implicit finite difference method to transform partial differential equations into algebraic difference equations. Moreover, the short‐term gas flow directions are specified and SOC relaxations are used. Simulation results on an integrated IEEE 24‐node system and Belgian 20‐node gas system verify the effectiveness of the proposed SOC models. The impacts of wind power forecast errors on multi‐period gas network operations are also investigated. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) play a critical role in the future energy Internet pattern. Therefore, proper models for the simulation of complex systems with multiple MMCs are required. This study proposes a simplified equivalent model (SEM) based on the implicit trapezoidal method and Thevenin equivalent. The model can accurately simulate arm voltages of the MMC and is thus capable of simulating system‐level transients after faults and disturbances, circulating currents and subsynchronous oscillation components. Subsequently, a hybrid model combining SEM and a detailed equivalent model (DEM) is built to improve the overall simulation speed in scenarios where submodule‐level transients are mixed with system‐level ones. Finally, this study notes that the major difference between DEM and SEM results only from the voltage‐balancing cycle. An experiential formula is given to regulate SEM when the voltage‐balancing cycle is large, where the difference may become obvious/insufferable. [ABSTRACT FROM AUTHOR]

Effective control measures taken on the transient potential energy distribution in power transmission network can not only improve the stability of power system but also reduce the probability of cascading failures occurrence. By researching the distribution variation rules of voltage, phase‐angle difference, potential energy and its margin in the three‐machine system, the relationship is revealed further between transient potential energy distribution and network structure. The potential energy distribution mainly depends on the topology structure and parameter of the network, the potential energy is distributed most easily in the vulnerable links where equivalent reactance is bigger and voltage is lower. Three control measures are proposed to relieve the accumulation of transient potential energy. Changing network structure and parameter in vulnerable links can perfect the internal structure of power network from the root, and then improve the resisting disturbance capacity of the power system. Whereas decreasing the transmission power in the vulnerable links is an emergency control measure for improving the operation stability of power system on‐line. Simulation results on wepri‐36 system testify the validation of the proposed method. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) grid‐connected inverter is the core component of PV generation system; quickly and accurately obtaining the parameters of inverter controller has great significance in analysis of transient characteristics of PV generation system. Parameter identification relies on disturbance signals and measurements selection, and the trajectory sensitivities of inverter controller parameters are calculated with different system outputs as the measurements, the disturbance signals include AC three‐phase short‐circuit fault and DC voltage reference jump, accordingly, a two‐step identification method is proposed, the first step use a three‐phase fault to identify all voltage loop parameters and the proportional coefficient of current loop, and the second step consider a DC voltage reference jump disturbance to identify the integral coefficient of current loop and the setting inductance value. The adaptive differential evolution is taken as the identification algorithm, which adopts adaptive strategies for algorithm parameters in order to speed up the convergence and enhances the balance between the global search and local mining. The simulation analysis validates the effectiveness of this method. In addition, the impact of the inductance error on the identification is discussed. [ABSTRACT FROM AUTHOR]

This study exhibits the optimum design procedure to tune controller parameters for grid‐connected distributed generation system based on cuckoo search algorithm (CSA). To investigate the effectiveness of proposed algorithm, a grid‐tied photovoltaic (PV) system consisting of two power electronic converters controlled by five proportional integral (PI) controllers is chosen. Setting proper values for all the PI controllers is a complicated task, notably when the system is non‐linear. In this study, response surface methodology (RSM) is used to develop the mathematical design of the PV system which is required to apply the optimisation algorithm. To minimise the design efforts of RSM, an alternate approach based on artificial neural network is introduced to develop the mathematical model of the PV system which is another salient feature of this research. Moreover, two modifications in the CSA are proposed to extract optimum parameters for the controllers which are found suitable in power system applications. Both the transient and dynamic performances of the system with the optimum values obtained through CSA are studied for different types of grid fault conditions using PSCAD/EMTDC. The design values are compared with values obtained through genetic algorithm and bacterial foraging optimisation. Experimental validation is also given for the proposed method. [ABSTRACT FROM AUTHOR]

Grid voltage disturbances result in high magnitudes of rotor currents and DC‐link voltage of the doubly‐fed induction generator based wind turbines (DFIG‐WTs), which may lead under severe fault conditions into deactivation of the machine side converter (MSC) and violation of the fault ride through (FRT) requirements of the grid codes. In this essence, several solutions were proposed, which vary between installing extra hardware components and control modification. However, the extra costs as well as the control limitations degrade the feasibility of the proposed solutions. In this study, new techniques are proposed to enhance the FRT through peak short‐circuit current reduction of the DFIG‐WT. The new techniques are developed based on the open‐loop and close‐loop dynamic response of the DFIG. The new techniques utilise the available MSC voltage, in order not to violate the voltage limits, to increase the rate of change of the DFIG internal transient voltage and to increase the magnitude of the transient impedance. Additionally, the mean variance mapping optimisation is used to optimally tune the gains in the second two techniques. The new techniques were implemented in a manufacturer‐based simulation model, and the simulation results show their effectiveness, where the maximum peak current reduction achieved was 23.6%. [ABSTRACT FROM AUTHOR]

The authors present new results regarding the analysis of voltage transients induced by switching capacitors in power delivery systems. Their approach is based on a systematic technique that facilitates the computation of initial conditions when the switch occurs. This set‐up permits an efficient parametric exploration that is suitable for accomplishing safe voltage peaks according to customer specifications. The authors discuss upper and lower bounds corresponding, respectively to (i) the worst‐case scenario in a lossless system, and (ii) the damped case with a shunt load and equivalent series resistances. Experimental measurements corroborate the underlying principles and results presented in this study. [ABSTRACT FROM AUTHOR]

A new approach to the analysis of the transient energy interaction in power systems is presented in this work on the basis of an analogous elastic network. A power system is first rigorously mapped to an elastic network consisting of elastic branches with different elasticity coefficients. On the basis of elasticity mechanics and the analogous elastic network, the transient energy of the different parts, such as the synchronous generators, branches, and loads, is defined and has been proved to agree with the law of energy conservation. Subsequently, based on the law of energy conservation and energy feature analysis, the concept of the power system energy structure (PSES) is built to exhibit the distribution and interaction of transient energy in the power system. Wide area and local area transient energy interaction can be analysed using the measurement‐based energy structure, which shows obvious potential in on‐line monitoring and analysis of power system oscillation. Finally, the simulations of Western Systems Coordinating Council (WSCC) three‐generator test system and a practical power system are performed and analysed to verify the rationality of the analogous elastic network and the validity of the proposed PSES. [ABSTRACT FROM AUTHOR]

An auto‐buck–boost single‐inductor multiple‐output (SIMO) dc–dc converter with duty‐cycle‐constrained comparator control is presented in this Letter. Combined both comparator‐based and duty‐cycle‐constrained controllers enable the dc–dc converter attaining fast transient response and low cross‐regulation (CR). The proposed algorithm is independent of the precision of current sensor and suppresses CR robustly with the proposed tri‐feedback loop control of comparator‐based voltage control, duty‐cycle‐constrained distribution and average current control. The proposed scheme is suitable for auto‐buck–boost SIMO dc–dc converter design for dynamic voltage scaling applications. [ABSTRACT FROM AUTHOR]