Real Time Digital Simulator Research Articles

Hardware in the Loop-Based Testing of Three Schemes for Mitigation the Effect of Unsymmetrical Grid Faults on DFIG

This paper presents three-proposed schemes to mitigate the effect of unsymmetrical voltage sag fault on a wind-driven grid-connected Double Fed Induction Generator (DFIG). The first tested scheme comprises a static compensator (STATCOM) connected to the DFIG stator, while a three-phase parallel RL external impedance is connected to the rotor circuit in the second scheme. The STATCOM and the added rotor impedance are connected simultaneously in the third scheme. The effect of applying the three schemes on the responses of the stator and rotor voltages and currents, the dc-link voltage and current, the electrical torque, and the rotor speed during an unsymmetrical voltage sag are presented and compared at sub-and super-synchronous speeds. All systems were emulated, implemented, and tested through an OPAL RT-4510 Digital Real-Time Simulator (DRTS) in a Hardware-In-the-Loop (HIL) application. The internal Field-Programmable Gate Array (FPGA) chip assisted in using this platform as a Rapid Control Prototyping (RCP) for virtual mitigation control and testing. The Matlab/ Simulink RT-lab software packages combination helped in the RT development environment. All real-time waveforms of parameters for the proposed scenarios were monitored through the HIL-controller and data acquisition interface and then compared with the simulated results. The results reveal that the simulation waveforms and the real time waveforms are congruent. Results prove the better performance of the DFIG during unsymmetrical voltage sag for sub-synchronous speed when applying both protection schemes, while best results are obtained when using only the rotor impedance at super-synchronous speed operation of the DFIG.

Distributed intelligence for consensus-based frequency control of multi-microgrid network with energy storage system

Multi-Microgrids (MMGs) provide a highly promising approach for accommodating diverse distributed energy resources and improving the overall system performance. This enhanced performance encompasses aspects such as reliability, resilience, flexibility, and energy efficiency. As MMGs become more prevalent, the conventional centralized control approach struggles to adequately address the coordinated operation of system. Therefore, this article proposes a leader-follower-based distributed control strategy (DCS) for coordinated frequency control of numerous heterogeneous and geographically dispersed DERs in MMG network. The DCS employs a robust nonlinear fractional-order proportional integral derivative controller for frequency control of MMG. To optimize the parameters of the controller, an adaptive hybrid chaotic atom search-particle swarm optimization (ACAS-PSO)-based distributed intelligent technique is proposed. Initially, the proposed control strategy efficacy has been tested against various single/multidimensional benchmark functions. Then, it is applied to optimize the parameters of the controller for frequency regulation of MMG system by minimizing the integral absolute error (IAE). The findings obtained illustrate that the proposed ACAS-PSO control technique has an IAE improvement of 42.21 % to 65.3 % in MG 1, 55 % to 96 % in MG 2 and 42.2 % to 84.5 % in MG 3 compared to state-of-the-art. Moreover, the proposed method enhances the frequency response in terms of settling time by 23.4 % to 68.7 % in MG 1, 45.2 % to 68.3 % in MG 2 and 36.35 % to 48 % in MG 3, and the control effort is enhanced by 31.2 % to 87.6 % in MG 1, 31.3 % to 87.05 % in MG 2 and 31.25 % to 73.2 %, in MG 3 compared to other techniques presented. In addition, the robustness of the proposed DCS is validated against plug-and-play ability, communication failure, and delays. Further, the proffered controller is validated by implementing in real-time digital simulation using OPAL-RT.

Power quality improvement of utility-distribution system using reduced-switch DSTATCOM in grid-tied solar-PV system based on modified SRF strategy

Abstract This paper describes a three-phase VSC based 4-switch Grid-Tied Solar PV-DSTATCOM using Modified Synchronous Reference Frame (MSRF) Theory to achieve the Unity Power Factor (UPF) operation, Zero Voltage Regulation (ZVR) operation, perform harmonics compensation and compensation against load unbalancing. The DC-Link voltage is set stable and voltage balancing is done across the split-capacitors under all load-charge conditions. Coordinated design of DSTATCOM consists of integrated Grid-Tied Solar Photovoltaic (PV) array and a DC-to-DC boost converter circuit for improvement of Photovoltaic energy/power. Maximum Power Point Tracking (MPPT) is used to provide the fixed power which is trapped and transferred from the array to the boost converter. UPF operation and ZVR are not available together. So, models are designed separately to accomplish one of the objectives (UPF and ZVR) for linear, non-linear and unbalanced loads. Simulation models are first designed in MATLAB software and then in Real-Time using RT-LAB having MASTER and CONSOLE blocks for Computation and Communication. In building of the model, Real-Time Digital Simulator (OPAL-RT 4510) is used in which hardware synchronised models are embedded, and hardware real-time results are displayed on the synchronised four-channel oscilloscope RIGOL-MSO5204.

Precise PMU-Based Localization and Classification of Short-Circuit Faults in Power Distribution Systems

Knowing the exact location of a short-circuit fault in a power distribution system (PDS) is essential for rapid restoration of service to customers and has a direct impact on the operational costs and reliability of the system. In this paper a phasor measurement unit (PMU) based method for fault localization and classification is presented. By introducing the concept of a virtual bus, the exact fault location on the line is determined rather than just a bus closest to the fault. Moreover, after determining the fault location, a generic fault model (GFM) is introduced to classify the type of fault by solving a minimization problem, which also provides fault impedances as a result. These can then be further used to determine if the fault occurred on the lateral instead of the main feeder without using additional PMU at the end of that lateral. The effectiveness of the proposed approach is verified by simulating various fault scenarios in two test systems based on real PDSs using a real-time digital simulator. In addition, a sensitivity analysis of the method is performed for different noise levels in the input parameters to verify its applicability to the real system.

Real Time Voltage Stability Estimation under Contingencies by Generalized Curve Fit Method using PMU

An accurate voltage stability monitoring scheme is necessary to take possible remedial action. Recent developments in Phasor Measurement Units (PMUs) technology provide the foundation for online voltage stability monitoring of a power system network. In this paper, the generalized curve fit method using PMUs in the system has been used to access voltage stability of the system and a sensitivity based approach has been used to identify critical buses of the system. Voltage stability margin has been obtained and compared using generalized curve fit method and continuation power flow method using PMUs in the system. Variations in voltage stability margin caused by changing load patterns have also been considered while estimating voltage stability under contingencies. Nose curves obtained using generalized curve fit and continuation power flow methods are also compared. Case studies have been performed on a standard IEEE 14-bus system and practical 246-bus Northern Regional Power Grid (NRPG) system representing power network of nine states of India, with the help of Real Time Digital Simulation (RTDS) and Power System Analysis Toolbox (PSAT) software.

Spatiotemporal Pattern Analysis of Nodal Inertia Using Convex Combination of Walks of Generator Nodes in Varying Inertia System

The distinct requirement of high control and faster frequency regulation from wind turbine generator (WTG) needs to look at the network's local and global vulnerabilities. In line with the above objective, the article elucidates 1) The role of generation units' contribution in handling the disturbances and their propagation in the network, and 2)The behavior of dynamic response of the nodes in the presence of faster frequency regulation action from WTG. The authors propose a novel online Nodal Inertia Index (NII) that considers the network's structural features and generator dynamic response in the varying inertia system. NII investigates the inherent property of the distribution of inertia in the system by the concept of graph theory convex combination of walks of generator nodes. Further, the article explores the dynamic response of nodes (DRN) in terms of disturbance location from the generator bus and also considers generators' internal interactions. DRN employs the Fiedler vector to observe the global response and locational impact. The application of NII and DRN in selecting reserve percentages of the WTG is showcased. All the analyses are performed in the modified IEEE 9,39 and 68 bus, coordinating between the Real-Time Digital Simulator (RTDS) and MATLAB platform.

Reconfigurable and Privacy-Preserving Economical Operation for Interconnected DC Microgrid Clusters

This article presents a new distributed and reconfigurable strategy for global economical consensus operation of multiple, interconnected dc microgrid clusters in a leader–follower graph architecture. The generation costs associated with the distributed energy resources are optimized globally by observer-based controllers in a multilayered hierarchical control structure, equipped with privacy-preserving feature. Self-rearranging and event-based reconfiguration of graphs are also incorporated for obtaining feasible solution to the economic dispatch problem. This is an important aspect of the proposed work as, unlike previously reported research works, it equally prioritizes both voltage regulation and optimal operation. Moreover, continuity of supply to critical loads is a challenging criterion in autonomous systems in which the pinning or leader node plays a pivotal role. Therefore, the multifold benefits of choosing the highest generation unit as the leader in improving the power quality is highlighted for the first time, which remained undiscovered in previous works in literature. The feasibility of the proposed scheme is tested by time-domain simulations in MATLAB/Simulink. Moreover, the results obtained from the controller hardware in loop environment using a real-time digital simulator and field-programmable-gate-array-based WAVECT controller demonstrate the economical operation of the clusters with renewable energy sources.

Ancillary Services and Risk Assessment of Networked Microgrids Using Digital Twin

The networked microgrids (NMGs) have become one of the better means of improving the resiliency and reliability of power system networks. NMGs need proper coordination of all microgrids in either grid-tied or isolated mode. This study proposes the use of a digital twin (DT) for the energy management of NMGs in the distribution system. The NMGs are virtually represented using a neural network (NN) by training the data from the different optimal results of unit commitment (UC). The UC formulation of NMGs considers risk assessment due to uncertainty of demand and renewable energy when the NMGs are operated in isolated mode and schedules ancillary service transactions when the NMGs are connected to the power grid. The NN predicts the schedule of diesel generators, fuel cell (FC) and the battery energy storage system (BESS) in both isolated and gird-tied modes. The merit of the proposed method is that the virtual model (NN) can interact with the physical model (NMGs) in a real-time manner that depends on its operational mode. Restated, the virtual model can provide real-time dispatch updates in the schedule of conventional generators, FC and BESS. A real-time digital simulator (Opal-RT eMegasim) was used to validate the proposed method by testing a modified CIGRE benchmark model and a modified IEEE 34-bus system.

Cyber-Secure Global Energy Equalization in DC Microgrid Clusters Under Data Manipulation Attacks

Cyber physical microgrids (MGs) are vulnerable to data manipulation attacks which can lead to significant imbalance in the MG. For instance, data manipulations by cyber adversaries may cause to higher loading of batteries with low state-of-charge. This will lead to degradation of the cycle-life of batteries unless timely intervention is done for malware detection. Therefore, a cyber-secure global energy equalisation of battery energy storage systems in multiple interconnected direct current (DC) MG clusters is proposed in this article for efficient utilisation of batteries. Cyber security is achieved in the framework through the proposed multi-level detection and mitigation paradigm aided by event generators. Firstly, it is the maiden attempt to propose and design a secure global energy equalisation framework for MG clusters. Secondly, the proposed event generators enable segregated defensive actions for leader and follower nodes in the network. This is unlike previously reported works wherein the defense mechanism has been generalised for every node. Further, the results indicate that the proposed event generators help in maintaining continuity of power to critical loads in the system. Extensive time-domain simulations are performed in MATLAB/Simulink under various practical scenarios of ad- versarial intrusions. Controller hardware-in-loop tests employing real-time digital simulator (RTDS) and field programmable gate array (FPGA) based WAVECT Controller are also performed for real-time validation of the proposed technique. Finally, for testing scalability of the algorithm, it is extended to 20 DC-DC converters.

Intelligent Power Control of Inverter Air Conditioners in Power Systems: A Brain Emotional Learning-Based Approach

Inverter air-conditioning (IAC) units have been proved to be effective in frequency regulation by providing flexible capacities. This paper proposes a brain emotional learning (BEL)-based controller to provide the IACs with control signals to be efficiently involved in the frequency regulation in power systems. The BEL-based controller can learn quick-auto, making it appropriate in systems facing uncertainty. To assess the BEL controller performance in realistic conditions, the uncertainties as a consequence of variations in system parameters and load level are considered. The goal is to use the BEL controller to increase the IAC units' ability to track regulation signals accurately in uncertain circumstances. The controller is compared to a fuzzy-PI control, a proportional control scheme, a model predictive control and a linear quadratic regulator control. A delay-dependent stability criterion is used to calculate the highest time delay in the IACs response under which the system maintains stability. In addition, this paper presents an BEL-based coordinator to coordinate the IACs and traditional generation units for compensating considerable frequency variations caused by the time delays. Case studies are accomplished on a multi-area power system in MATLAB/Simulink environment. Eventually, real-time verifications by OPAL-RT real-time digital simulator on the simulated power system are executed to assess the control method.

Improving the power quality and hydrogen production from renewable energy sources based microgrid

The world is looking for utilization of renewable energy sources to reduce global warming as well as the consumption of fossil fuels. In this scenario, solar and wind energy are widely used at many places worldwide. However, both solar irradiance and wind speed are depending on nature. Hence, an energy storage device must be required to operate at their best utilization level by converting them to electricity. One of the best energy storage devices for medium power range is the battery. However, batteries require high maintenance and suffering from self-discharge as well as storage capacity will be decreased day by day. Hence, storing hydrogen can be an economically feasible solution instead of using batteries for high power range. Usually an aqua electrolyzer can easily convert water to hydrogen and oxygen through electricity. However, due to slow dynamics of heat transfer from electricity, the generation of hydrogen cannot meet the fast response like electrical devices. Therefore, a novel controlling technique is required to increase the production quality of hydrogen during random changes in both solar irradiance and wind speed. In order to achieve the best utilization, both photovoltaic panels and wind turbines are operated at their maximum power point levels. In this research boost converters are used to operate as maximum power point tracking devices. The whale optimization technique is integrated to respective controllers of all the converters to achieve stable production of hydrogen during rapid changes in irradiance and wind speed. The Whale Optimization Algorithm (WOA) technique is compared with Genetic Algorithm (GA), Particle Swarm Optimization (PSO) and Grey Wolf Optimization (GWO) to show the benefits of tracking response of the system on improving production of hydrogen from hybrid renewable energy sources based Microgrid. Hardware—in the—Loop (HIL) is developed to analyze the results with the help of OPAL-RT modules. Along with HIL results, a Real Time Digital Simulator (RTDS) based results are also presented to evaluate the performance of the proposed method.

Pilot protection method of half-wavelength AC transmission lines based on random matrix theory

The fault characteristics of ultra-high voltage (UHV) half-wavelength (HWL) transmission lines exhibit significant differences from those of conventional transmission lines, which renders the conventional relay protection method unsuitable for ensuring the protection of HWL. To solve this problem, a pilot protection method of HWTL based on random matrix theory was proposed. Voltage and current fault components obtained at the protection installation on both sides of the line were used as the input of the random matrix to form the singular value equivalent matrix, and the eigenvalues of the random matrix at both ends were calculated. The faults inside and outside the area were determined according to the distribution of the eigenvalues in the circular plane area. The protection scheme avoids the data synchronization problem at both ends of the line. Real time digital simulation system (RTDS) simulation revealed that the proposed protection method can protect the full length of the line, is suitable for various fault types and fault conditions, and exhibits excellent resistance to transition resistance.

Mitigation of power system oscillations in weak grids with battery energy storage systems: A real-world case study

Sub-synchronous oscillations are becoming commonplace in weak areas of power systems with high levels of renewable generation, affecting their operation. Moreover, there is a lack of methods and techniques that facilitate the understanding of such phenomena and the analysis of mitigation alternatives from a practical-knowledge point of view. In this manuscript, the combination of static and dynamic techniques is utilized and consolidated to derive general conclusions when mitigating sub-synchronous oscillations by means of grid-forming battery energy storage systems (GFM BESSs). The grid impedance shaping effect of GFM BESSs, which allows the mitigation of undesired oscillations, is demonstrated through small-signal (static) and frequency scanning (dynamic) analyses when studying an actual and extremely weak grid, the Australian West Murray Zone. These findings are further validated when performing detailed real-time EMT digital simulations of the grid. Furthermore, additional dynamic simulations demonstrate the ability of GFM BESSs to provide system strength and increment the hosting capacity of renewables in weak areas. The methods and techniques presented in this work can be applied to any power system, further supporting existing industry practices.

Power Differential Protection for Transformer Based on Fault Component Network

Current differential protection has been widely used as the primary protection of transformers. However, inrush currents during transformer energization can cause misoperation of the protection when the second harmonic restraint algorithm fails. This paper proposes a power differential protection scheme based on the fault component network (FCN), which is free from inrush detection and computationally cheap. First, the fault component differential power (FCDP), defined as the differential active power of a transformer in the FCN, is analyzed under different conditions. Second, a transformer protection scheme is presented based on the FCDP and the traditional differential power. A removal algorithm of decaying direct current (DDC) offset is developed to accurately estimate the FCDP. The performance of the scheme is tested under various conditions, including internal faults, external faults and transformer energization. The simulations using PSCAD, and Real Time Digital Simulator (RTDS), experiments in the Electrical Power Dynamic Laboratory (EPDL) and real recording data validate that the proposed method can protect the transformer reliably.

Deep-Learning-Based Denial-of-Service Resilient Framework for Wide Area Situational Awareness of Power Systems

Vulnerability of the wide area measurement system (WAMS) to Denial of Service (DoS) attacks can hinder the real-time situational awareness of the grid. In this regard, a DoS cyber-attack resilient WAMS framework is presented, which utilizes deep-learning based overcomplete denoising autoencoder (ODAE) architecture. The proposed framework is able to reconstruct PMU data during DoS attacks on PMU-PDC connections for the entire period of power system contingencies, which helps the operator to be aware of the occurrence of any such disturbance and assist them in decision making related to the stability of the grid. The performance of the proposed framework has been validated on WSCC 9 bus system, which is simulated on the developed cyber-physical WAMS testbed involving real time digital simulator (RTDS), hardware PMUs, Hardware PDC, network switches etc. Subsequently, the response of the suggested framework has also been evaluated on the real field PDC data gathered from the Northern Region of the Indian Power Grid (NRIPG). The experimental results indicate that the reconstructed PMU measurements during DoS attacks help in maintaining the dynamic visualization of system-wide information thereby ensuring the resiliency of wide area monitoring applications against DoS attacks.

A novel decentralized inverter control algorithm for loss minimization and LVRT improvement

Algorithms that adjust the reactive power injection of converter-connected RES to minimize losses may compromise the converters’ fault-ride-through capability. This can become crucial for the reliable operation of the distribution grids, as they could lose valuable resources to support grid voltage at the time they need them the most. This paper explores how two novel loss-minimizing algorithms can both achieve high reduction of the system losses during normal operation and remain connected to support the voltage during faults. The algorithms we propose are decentralized and model-free: they require no communication and no knowledge of the grid topology or the grid location of the converters. Using local information, they control the reactive power injection to minimize the system losses. In this paper, we extend these algorithms to ensure the low voltage ride through (LVRT) capability of the converters, and we integrate them with state-of-the-art Wavelet-CNN–LSTM RES forecasting methods that enhance their performance. We perform extensive simulations on the real-time digital simulation (RTDS) platform, where we demonstrate that the algorithms we propose can achieve a substantial decrease in power losses while remaining compliant with the grid codes for LVRT makes them suitable for the implementation across the distribution system.

Operational Issues on Adaptive Protection of Microgrids Due to Cyber Attacks

This paper shows how false data injection attacks (FDIAs) affect adaptive projection in microgrids. Specifically, we implemented a directional over-current relay in the CIGRE low voltage benchmark system to carry out experiments to manipulate protection decisions via cyber-attacks. The aim of the newly proposed cyber-attack is to cause false relay tripping and unbalanced conditions in microgrid that can result in power outages and blackouts. The proposed study has been validated on commercial relays using a real-time digital simulator equipped with the IEC 61850 standard communication protocol. These results allow the power systems engineers to understand the cyber-physical interactions more closely and adapt their protection schemes accordingly.

Implementation of Control Standardization Based on HCM5000G DC Control and Protection Platform

This paper introduces the whole construction of the control standardization simulation system based on the HCM5000G DC control and protection platform, which can meet the requirements of engineering design and various control performance indexes by adopting the standardization design of the self-control and localization platform. In this paper, the construction principle of the standardized control system and the optimization strategy of the control structure are discussed in detail, and the engineering simulation model is realized by using the real-time digital simulation system with the layered and distributed standardized interface design, which provides an important reference for the future large-scale application of the control and protection of DC Engineering.

A novel negative feedback phase locked loop-based reference current generation technique for shunt active power filter

The use of nonlinear devices introduces current and voltage harmonics into power distribution networks. The presence of harmonics, an undesirable power quality issue, causes transformer overheating, malfunctioning of sensitive loads, power losses, and significantly reduced distribution system efficiency. Therefore, harmonics mitigation in power systems has become absolutely essential and is widely addressed, utilizing shunt active power filters (SAPFs) around the globe. The performance of SAPF in generating adequate compensating current depends on the working of three control loops used for the purpose of reference current generation, dc-link voltage control, and switching pulse generation. The existing approaches for reference current generation suffer from inherent complexity and the inability to extract positive sequence signals required for obtaining synchronizing angle during source disturbance conditions. Therefore, this paper proposes a novel negative feedback phase-locked loop-based modified synchronous reference frame technique to overcome the drawback of the existing approaches. The effectiveness of the proposed approach is investigated under ideal and non-ideal grid voltage conditions with different load perturbations. The proposed control strategy is first tested using a number of simulation-based experiments and, thereafter, validated using OPAL-RT 4510 real-time digital simulator. Compared to other existing approaches, the proposed technique has offered improved results in terms of reduced total harmonics distortion.

A non-unit line protection method for MMC-HVDC grids based on the curvatures of backward traveling waves

The existing protection techniques for high-voltage direct-current (HVDC) grids suffer from several shortcomings such as high sampling frequency, poor robustness, and reliance on simulation for threshold setting. To solve these problems, this paper proposes a non-unit protection method for modular multilevel converter (MMC)-based HVDC grids using the curvatures of backward traveling waves. To this end, the propagation characteristics of traveling waves and the boundary characteristics of DC lines are first studied, then the analytical expressions of backward traveling waves are derived. Moreover, the curvatures of backward traveling waves are analyzed. On this basis, a non-unit protection method is proposed, including zone selection, disturbance identification, and pole selection. At last, with a protection platform and a real-time digital simulator (RTDS) platform of the MMC-HVDC grid, the accuracy and the robustness of the proposed protection method are verified. The results show that the protection method can correctly identify faults with different distances and resistance in 1 ms and has strong robustness against transition resistance, sampling frequency, boundary value, noise, system topology, and line parameters.