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Frequency is a useful parameter for ensuring the proper functioning of the power system operation, control, and protection. In this paper, a fast and accurate frequency estimator is developed using a Zero-crossing and a Peak, occurring in the buffered data instead of two Zero crossings, which is commonly used to measure the frequency. Prior to this, the signal is preprocessed using the Sliding Goertzel Filter (SGF) that mitigates the impact of undesirable features such as harmonics, noise, etc. from the signal. The two frequency estimators, with and without SGF, then work in parallel to form the hybrid estimator and named as $Z_{C}P_{k}-HFE$. The estimated frequency is chosen based on the minimum error computed from the two parallel estimators. The performance of the estimator is, then, validated using the simulated signals polluted with harmonics, noise, transients etc. Moreover, the evaluation results with the IEEE-13 Active Distribution Network (ADN) incorporated with Photovoltaic DG using and dSPACE1104 and Real Time Digital Simulator (RTDS), show its capability to estimate real-time frequency with satisfactory output.

With the integration of the large-scale wind farms, the conventional pilot protection is facing new challenges. It suffers from the performance degradation can even refuse operation for some extreme faut scenarios. To address this problem, this paper presents a novel pilot protection based on cosine similarity. The protection setting calculation and industrial application testing is investigated. The functional structure is described and the logic of the cosine similarity based protection is evaluated under different fault scenarios. Compared with the conventional differential protection, application of the proposed protection can greatly improve the relay performance. The proposed protection is embedded into an industry relay device, the standard hardware-in-loop tests are carried out using the real time digital simulator (RTDS) before the industrial application. Now the protection device based on cosine similarity is installed in the wind farms and put into operation in Inner Mongolia.

Distance relays are quite vulnerable to maloperation during dynamic stressed situations. The apparent impedance seen by the relay encroaches the zone-3 resulting in distance relay maloperation that can initiate cascading failures. This paper presents an enhanced scheme for wide area backup protection which implements improved protection algorithms to decide final relaying status. A machine learning tool namely Deep Neural Network is utilized to build those protective relaying decision logics: RDL-1 and RDL-2. Wide area information retrieved from phasor measurement units (PMU) is used to take real time decisions. RDL-1 is designed to detect if the system is operating in normal or stressed condition. During normal state, traditional zone-3 relay undertakes the relaying decision. However, under stressed situations, RDL-1 switches the decision-taking to RDL-2. RDL-1 also predicts whether the system is progressing towards an out-of-step situation so that appropriate remedial action can be undertaken. Proposed scheme was studied on IEEE-39 bus New England system using MATLAB/SIMULINK and validated on Real Time Digital Simulator platform and third zone mal-tripping are avoided. Performance of the proposed algorithm was compared with the conventional blinder and other data-mining techniques which show considerably high classification accuracy.

The main challenge of the microgrid is to design a suitable protection scheme due to the complexity of the architecture of the microgrid. The importance of the proposed protection technique is threefold. First, it presents a co-simulation platform to integrate between a simulated model on power system computer aided design (PSCAD)/real time digital simulator computer aided design (RSCAD) software's and physical devices schweitzer engineering laboratories (SEL) 421-7 relays to protect the microgrid that includes different resources connected based on inverter interface. Second, it presents a comprehensive hardware/software setup to test the protective relays in a closed loop system and shows how to configure the protective relay's International Electrotechnical Commission 61850 communications. Third, IEEE 1588 standard is used to provide sub nanoseconds latency between the simulated model that emulated on real time digital simulator (RTDS) and the external devices. Also, the measurement signals are synchronized between RTDS and the external devices using giga-transceiver synchronization card (GTSYNC) interface card and SEL-2488 satellite-synchronized network clock. The results showed that the co-simulation infrastructure introduces a highly dependable design, analysis, and testing environment for cyber and physical data flow in the system. Besides that, the voltages at ac/dc sides and frequency at fault condition were maintained due to the energy storage device contributions at different modes of operation.

The emerging trends in the microgrid development and the increasing penetration of distributed energy resources (DERs) in the distribution networks urge the modification in the existing conventional protection techniques. The integration of DERs changes the radial nature of the network, and thus, the schemes designed for such networks fail to operate for the microgrid system. Hence, a new fault detection technique is required for the microgrid system. In this article, a new fault detection scheme is developed for detecting the low-impedance faults (LIFs) as well as high-impedance faults (HIFs). The detection of HIFs is of major concern as these faults lead to a very low fault current value, which makes them undetectable by the conventional overcurrent relays. The proposed scheme uses the cumulative sum value of the differential negative-sequence impedance angle (DNSIA) as the fault detection parameter for generating the trip signal. The simulation results show that the proposed method effectively detects LIFs and HIFs accurately. The proposed scheme is independent of the type of faults, type of DGs, and the value of fault impedances. Furthermore, the proposed scheme also discriminates between the switching transients and faults effectively. The IEEE 13-bus test system is modeled and simulated on real time digital simulator (RTDS)/RSCAD platform. The method is further validated for the real-time implementation by developing the experimental setup for performing the control hardware-in-the-loop.

This article demonstrates the modeling of a real engine-generator set (genset) based on manufacturer data for use in controller-hardware-in-the-loop testing of microgrid control systems. The simulation environment used is RTDS Technologies’ real time digital simulator using PB5 cards. In addition, this article provides detail on integration of a commercially available controller with the simulator analog and digital inputs and outputs for control of the simulated genset. Testing of the developed model is performed to validate the standard parameters of the synchronous generator and the dynamic performance of the genset during starting, load acceptance, and load sharing between multiple gensets. By integrating controller hardware, time spent on modeling the genset frequency, voltage, and load sharing controls is avoided and valuable simulator processing capacity is saved. The result of this investigation is a genset model that exhibits the characteristics of real equipment and may be used in the validation of controller hardware and software for the derisking of microgrid control systems.

In this article, power converters are used in the integrated wind farms and can change the fault characteristics of the power system. The conventional pilot protection suffers from low sensitivity, or even the risk of maloperation. In order to address these problems, the fault features of the transient current of various power sources are analyzed and a novel pilot protection based on cosine similarity is proposed. To validate the proposed protection, the real time digital simulator hardware-in-loop tests are carried out to verify the proposed method. In addition, a field short-circuit test is conducted in a real wind farm to examine the performances of the proposed protection. The results demonstrate that the proposed method can be potential option for industrial applications.

Parallel operation of distributed power converters is used to realize high rated power and low current ripples with low rated power devices. It is also being preferred since central compensators fail to identify power quality problems reflected on low voltage levels, especially with the new structure of microgrids. This article proposes a novel parallel operation between modularized distributed transformerless unified power quality conditioner (TL-UPQC) for low voltage distribution networks. The operation is intended to improve the grid voltage profile while considering the connected modules rated capacity. The proposed methodology is suitable for smart grid applications where multiple renewable energy sources are integrated with the network. An advanced control technique that allows monitoring, wireless communication and coordination between the connected modules is presented. The proposed control methodology allows modularity and operation flexibility. System characterization has been studied to evaluate the influences of communication delays on overall system stability. The system has been evaluated by controller hardware-in-the-loop testing methodology. The power stage is simulated in a real time digital simulator, while the control algorithm is developed in a digital signal processor. Experimental results including random behavior of a photovoltaic system are presented.

Simulation has been widely adopted as a support tool for the validation and experimentation of distributed systems. It allows different devices and applications to be evaluated and analyzed without requiring the actual presence of those machines. Although the simulation plays an important role in investigating and evaluating the behaviors of devices, it results in a serious simulator building problem as the distributed systems become more and more complicated and dynamically data driven. Most of the existing simulators are designed and developed to target a specific type of application, lacking the capabilities to be a configurable and standardized tool for researchers. To solve the adaptability and reusability problems of simulators, this paper proposes a new approach to design and implement a configurable real-time digital simulator for hardware devices that are connected via data buses in distributed systems. First, the proposed simulator uses a logic automaton to simulate the activities of a real device, and generates the incentive data for tested equipment according to the predefined XML-based files. Then with a virtual bus, the simulator can receive, handle, and send data in various network environments, improving the flexibility and adaptability of a simulator design. Experimental results show that the proposed simulator has a high real-time performance, and can meet the increasing requirements of modern simulations of distributed systems.

This paper presents an efficient power management, voltage balancing and grid synchronization control strategy to increase the stability and reliability of distributed energy resources (DERs)-based microgrid. The microgrid is composed of Photovoltaic, Double Fed Induction Generator-based wind and diesel generator with critical and non-critical loads. The system model and the control strategy have been developed in Real Time Digital Simulator. The coordination and power management of the DERs in both grid connected and island operation modes is implemented. One distinct challenge of microgrid operation in island mode is the stable control of frequency. A controller is proposed and implemented in the island mode for the diesel generator equipped with the required inertia to maintain the microgrid rated frequency by operating in the isochronous mode. To restore the microgrid back to the utility, the voltage, frequency and phase angle of the islanded microgrid should match with that of the grid network within specified limits to avoid transient instability. Switched capacitor banks are connected at the point of common coupling to balance the voltage for microgrid synchronization. The CIGRE medium voltage test bench system is used to implement the DERs and their controller. The proposed control approach has potential applications for the complete operation of microgrids by properly controlling the power, voltage and frequency in both grid and island modes. The real time digital simulator results verify the effectiveness and superiority of the proposed control scheme in grid connected, island and grid resynchronization scenarios.

Renewable energy (RE) generation levels are increasing in modern power systems at a fast rate due to their advantages of clean and non-exhaustible nature of energy. However, this type of generation creates technical challenges in terms of operation and control due to uncertain and un-predictable nature of generation. Islanding is an operational scenario where there is a loss of grid and RE generators continue to feed power to the local load. This has harmful effects on the RE generators and operating personal. Hence, it is expected that islanding scenario is identified in minimum time and RE generators are disconnected within $2~s$ duration after island formation. This paper designed an islanding identification scheme (IDS) by designing a current islanding detection indicator (CIDI) that combines the features computed by processing the current signals, negative sequence current (NSC) and negative sequence voltage (NSV) using the Stockwell transform (ST) and the Hilbert transform (HT). Information contained by the total harmonic distortions of voltage ( $THD_{v}$ ) and current ( $THD_{i}$ ) is also used while designing the CIDI. Islanding and non-islanding events of category-I & II are identified and discriminated from each other by comparison of peak magnitude of CIDI with the first threshold value (FTV) and second threshold value (STV). This IDS effectively recognizes the islanding events even in the noisy environment with minimum non-detection zone (NDZ) and minimum time. The efficiency is greater than 98% even with the noise of $20dB$ SNR (signal to noise ratio). The performance of proposed IDS is better compared to IDS using discrete wavelet transform (DWT), Empirical mode decomposition (EMD), Slantlet transform & Ridgelet probabilistic neural network (RPNN), and artificial neural network (ANN). The effectiveness of IDS is validated on IEEE-13 nodes test system using MATLAB software, practical distribution network and in real time scenario by use of real time digital simulator (RTDS).

In this study, a passive islanding detection technique based on the variation in the angles of superimposed sequence components of voltage and current is proposed. The pre- and post-islanding voltage and current superimposed components are derived using the corresponding voltage and current phasors. The angle between the positive and negative sequence voltage and current and the superimposed components of these quantities are derived to take further action. Furthermore, decisions obtained from the angles of different superimposed components are combined using a voting technique to take the final decision with more reliability and accuracy. The scheme does not require the establishment of any threshold and completely relies on the rule base obtained through a simulation study. A microgrid with multiple connection points is simulated using a real-time digital simulator (RTDS). A hardware-in-the-loop test bench is arranged using a dSPACE DS1104 and RTDS. Numerous test cases are simulated to assess the performance of the proposed technique.

The wide application of power electronic component in power system with renewable energy sources has changed the fault characteristics of conventional power system, resulting in the performance degradation of conventional protection, and even the risk of maloperation and rejection. This brings challenges to the security and stability of the power grid. Therefore, in order to solve these problems, a novel principle of pilot protection based on structural similarity and square error method is proposed. The structural similarity criterion makes use of the difference of fault characteristics between renewable sources and synchronous generators to identify internal faults, while the square error auxiliary criterion is used to solve abnormal calculation of the existing similarity based protection. The detailed model of grid-connected renewable energy power plant is built in Real Time Digital Simulator (RTDS) and the proposed protection algorithm is solidified in the industrial protection device. The effectiveness of the proposed principle is verified by hardware-in-loop dynamic simulation experiments. Compared with conventional differential protection, the proposed protection shows excellent performance in speed and reliability during various faults. In addition, a field short-circuit test is carried out in a real wind farm to verify the effectiveness of the proposed protection scheme. It is proved that this proposed method has the prospect for industrial application.

This study develops an energy management platform for battery-based energy storage (BES) and solar photovoltaic (PV) generation connected at the low-voltage distribution network. The sewage treatment plant of Gujarat International Finance Tec-City located in the Gujarat state is considered as a testbed. The contribution of this case study is twofold: (i) Formulation and lab-scale implementation of an optimal scheduling algorithm to charge/discharge BES while minimising the net energy purchase cost. (ii) Development of a fuzzy logic-based speed control strategy for aeration blower to enhance the process efficiency. A stochastic optimisation problem was formulated as mixed-integer linear programming to achieve the charging and discharging schedules of BES. The simulation study on speed control of aeration blower was carried out to demonstrate the air injection control for optimal dissolved oxygen level in the aeration basin at the testbed. Simulation results of the case study and lab-scale hardware realisation (through real-time digital simulator interfaced with modular hardware) were presented to validate the demand- and supply-side energy management platform.

The performance of salient-pole synchronous generators protection is of great importance for the stability of power systems, as they are present in large hydropower plants, subject to various abnormal operating conditions such as three-phase or two-phase faults, electromechanical disturbances and loss-of-excitation. In this context, this work proposes a testing philosophy of salient-pole synchronous generators, in order to define more accurately the setting of the protections and controls of this asset. Thus, in the developed methodology, the admittance plan (G-B) proves applicable to analyze the coordination between the loss-of-excitation protection and the underexcitation limiter, as an alternative to the power (P-Q) and impedance (R-X) planes, normally employed in literature. In modeling the problem, real data for both the hydrogenerators and the electrical network are used. The simulations were performed in a hardware-in-the loop scheme integrated by a Real Time Digital Simulator and a physical relay. Thus, analyzes are made for situations of stable power swing and partial and total loss-of-excitation. The results are useful to prove, through the monitoring of relevant variables of the hydrogenerators, the feasibility and accuracy of the G-B plane in the coordination between the protection and the control of the synchronous machine.

Standalone DC microgrids (SDCMGs) are emerging as prominent solutions to remote customers. As these SDCMGs mainly depend on renewable energy sources to curb carbon emission, reliability of the system is lessened due to their intermittent nature. The battery could offer a solution to this problem as it is inherently enclosed by DC grid for power balancing, but the purpose may not be served completely due to high capital cost and maintenance. Thus, the diesel generator (DG) becomes a major alternative to overcome this issue because of low investment, high compatibility, and flexibility. However, DG inhibits with cranking delay, sluggish response and low fuel efficiency under frequent switching and variable loading scenarios. To suppress the issues, a new power management strategy (PMS) is developed to ensure proper coordination between different sources, storage devices and loads in SDCMG. In addition to this, an effective control scheme is also proposed to achieve seamless regulation of DC bus voltage even under extreme conditions. In this study, different SDCMG configuration is considered for testing and simulation of system is carried out in real-time digital simulator to prove their viability. A scaled prototype is developed to validate simulation results and authenticate proposed PMS and control scheme.

In view of the complex correlation between Doubly Fed Induction Generator (DFIG) internal components and control links which makes it difficult to locate the oscillating source in the equipment level, a DFIG equipment-level oscillating source locating method based on dynamic energy flow is proposed. Firstly, the energy correlation topology network of DFIG internal components and control links is constructed. On this basis, the analytical expressions of dynamic energy flows of DFIG internal components and control links are derived. And then, through Partial Directional Coherence (PDC) analysis, the values of causality between dynamic energy flows of DFIG internal components and control links are calculated, and the diagram of DFIG internal oscillation transmission causality is depicted. Thus according to the distribution pattern of causality values in the causality diagram, the oscillation transmission route is identified and the oscillating source is located. Finally, simulation tests in Real Time Digital Simulator (RTDS) of IEEE 10-machine 39-bus system verify that, the proposed method can quantitatively describe the intensity of interaction between dynamic energy flows of DFIG internal components and accurately identify the oscillation transmission route and the oscillating source in the equipment level. The proposed method can accurately track the original control link/physical component that causes the system to oscillate. Therefore, this paper will facilitate research on DFIG parameter tuning and oscillation suppression measures for low-frequency oscillation in power system.

This article presents a new approach for classification and localization of voltage sags triggered by symmetrical and unsymmetrical faults in electricity networks. The proposed method utilizes five unique parameters of three-dimensional (3-D) polarization ellipse (PE) obtained from the mapping of three-phase voltage signals in 3-D coordinates. The decision boundaries, which are set by the parametric equations exploiting the five ellipse parameters, namely, elevation, azimuth, tilt angles, semi-major axis, and semi-minor axis, are used to classify the fault-initiated sags. The localization of faults is conducted from the parametric equations demonstrating the variation of ellipse parameters with respect to distance from the fault-location. These parametric equations would be helpful to make decision faster and thereby, eliminate the uncertainty in decision-making process. The applicability of the proposed method is tested and validated using real data measured by DOE/EPRI, the recorded waveforms of IEEE 1159.2 Working Group, and the data extracted from the simulation of faults at several feeders of IEEE 14-bus test system using RSCAD and Real Time Digital Simulator (RTDS) platform.

An artificial neural network (ANN) architecture for real-time estimation of available transfer capability (ATC) has been reported in this study. The real-time data obtained from phasor measurement unit (PMU) is utilised to generate target output (ATC) using the pattern search optimisation-based method. The set of information provided as input to the pattern search-based ATC optimiser along with its output forms the input and target output for ANN training. The input information consists of active and reactive power injected along with voltage and current vectors measured at PMU buses. The ATC optimiser is functional as long as ANN is under training. Once the ANN is trained, it receives input set directly from PMU and produces ATC values. PMU emulation is employed for archiving the PMU data. The proposed method is tested on modified IEEE 24-bus, IEEE 30-bus, and IEEE 118-bus test system. The proposed method has also been implemented on real-time digital simulator.

Fractional Frequency Transmission is a competitive technology for offshore wind power transmission. Modular Multilevel Matrix Converter (M3C) plays a key role in a Fractional Frequency Transmission System (FFTS) as the frequency changer. M3C is broadly considered as the AC–AC converter for the future with its attractive advantages in high voltage and high power applications. Due to the lack of a DC link, electrical quantities at different frequencies from two AC systems couple in M3C, resulting in a complex harmonic condition. Harmonics can lead to stability issues and its analysis is of great importance. This paper focuses on the harmonic analysis of M3C. The arm capacitor voltage ripples and the harmonic currents are analyzed at various frequencies. Major factors influencing the harmonics magnitude are discussed. Analysis is conducted on sub-module capacitance and arm inductance selection. A zero-sequence current mitigation controller for M3C is implemented and tested. It is found that for a FFTS, some current harmonics flow into AC systems even though the system is balanced, while the others circulate within the converter. The theoretical harmonic analysis is verified by simulations in Real Time Digital Simulator (RTDS) of a M3C system where each arm consists of forty sub-modules.

This paper presents a new adaptive technique to restore coordination between recloser and fuse of a distribution network in presence of distributed generations (DGs). The proposed technique is based on the derivation of modification factor (MF) which is defined as the ratio of the preset value of positive sequence impedance seen by a recloser $(Z_{1preset})$ to its calculated value $(Z_{1cal})$ . Based on the value of MF, the recloser fast time–current characteristic is altered. The value of $Z_{1cal}$ is obtained by acquiring samples of currents and voltages at the location of the recloser. Performance of the proposed scheme has been evaluated by modeling IEEE 34-bus network in real time digital simulator (RTDS)/RSCAD environment. At the same time, appropriateness of the proposed scheme has been verified on a practical setup developed in the laboratory. The results obtained from simulations as well as from the laboratory prototype indicate that the proposed scheme is able to restore coordination between recloser and fuse with a high as well as a low penetration of DG. At the end, a comparative analysis of the proposed scheme with the previously published schemes proves its superiority in restoring the recloser–fuse coordination.

During the life span of an instrument transformers (IT), non-catastrophic and typically undetected problems may degrades the overall performance of the instrumentation system. Synchrophasor provides high resolution synchronized data compared to the Supervisory Control and Data Acquisition (SCADA) systems. In the proposed non-intrusive method, time-series Phasor Measurement Units (PMUs) data are processed using three step approach for real time condition monitoring of IT at the control center. Bad data are filtered or flagged using MLE based ensemble method before applying density-based spatial clustering of applications with noise (DBSCAN) to detect clusters, changing over time within each time window. In the third step, a decision logic diagram is developed using additional data and system information to categorize the observed anomalies into different types of malfunction, failure, event or degradation. The proposed method has been validated using IEEE test system modeled in the Real Time Digital Simulator (RTDS) interfaced with industrial hardware PMU device. Detecting equipment failures at an early stage will result in improved system reliability and reduced maintenance cost. Several test cases demonstrate superiority of the proposed method for detecting incipient failures in the IT, and provides early warning mechanism for preventing full blown faults resulting in major impact on the power grid.

Voltage instability, power imbalance, and unreliability are all caused by power interruptions and losses in the distribution system. The optimal reconfiguration of the distribution network is offered in this research as a solution to such challenges. The investigation is carried out using an actual distribution system in Kombolcha, Ethiopia. Modified shark smell optimization (MSSO) is used in the MATLAB environment to improve system reliability and voltage profile with low power loss. Tie switches are optimally placed to reduce power losses, total cost of outages, and reliability indices such as the system average interruption frequency index (SAIFI), system average interruption duration index (SAIDI), and expected energy not supply (EENS) all at the same time. The MSSO's effectiveness is demonstrated through a comparison with other approaches. Furthermore, a real-time digital simulator is used to implement the suggested task in real time with allowable mistakes in the results (RTDS).

This paper presents a platform for conducting Power-hardware-in-the-loop (PHIL) testing of an electric vehicle (EV) motor controller implementing field oriented control (FOC). A fast-switching power-electronics-based amplifier is used to achieve the required transient response speeds necessary for emulating a three phase AC motor with a high fundamental frequency. A field programmable gate array (FPGA) is used to implement the bidirectional high-speed fibre-optic interface, communicating signals between the physical system and a real time digital simulator (RTDS) platform. This allows for a 1 microsecond simulation timestep and a total delay less than 4 microseconds. Using RTDS allows for the simulation to be developed through a traditional circuit simulator interface, rather than requiring a specialized simulation developed to run on an FPGA. Separately from the power amplifier, a resolver emulator system has been developed, allowing for all sensing systems of an EV motor controller to be validated before connecting a physical motor.

Connecting multiple microgrids to form interconnected microgrids can improve power distribution systems resiliency and reliability. However, there is uncertainty of balanced power sharing among multiple microgrids while interconnecting the microgrids. To address this issue, in this paper an intelligent module for interconnecting multiple microgrids with self-healing capability is developed by considering the power mismatch between distributed energy sources generation capacity and load demand of all the microgrids. The advantage of the proposed module is its circuitry is simple, flexible and real-time implementation is easy. To validate the performance of the interconnecting module, two microgrid testbeds are considered in this study and real time simulations are carried using real time digital simulator. The results obtained have ensured the efficacy of the developed intelligent interconnecting module.

The conventional Under Frequency Load Shedding (UFLS) scheme could result in unacceptably low frequency nadirs or overshedding in power systems with volatile inertia. This paper proposes a novel UFLS scheme for modern power systems whose inertia may vary in a wide range due to high penetration of renewable energy sources (RESs). The proposed scheme estimates the rate of change of frequency (RoCoF) of the center of inertia (CoI), and consequently, the loss of generation (LoG) size, using local frequency measurements only. An innovative inflection point detector technique is presented to remove the effect of local frequency oscillations. This enables fast and accurate LoG size calculation, thereby more effective load shedding. The proposed UFLS scheme also accounts for the effect of the inertia change resulting from LoG events. The performance of the proposed scheme is validated by conducting extensive dynamic simulations on the IEEE 39-bus test system using Real Time Digital Simulator (RTDS). Simulation results confirm that the proposed UFLS scheme outperforms the conventional UFLS scheme in terms of both arresting frequency deviations and the amount of load shed.