Islanding Of Distributed Generation Research Articles

Detection of faults and DG islanding in PV-Wind DC ring bus microgrid by using optimized VMD based improved broad learning system

This paper presents a novel approach for the detection and classification of photovoltaic with wind based DC ring bus microgrid DC faults and DG (distributed generation) islanding events. This novel approach consists of adaptive variational mode decomposition (AVMD) and an improved broad learning system (IBLS). Initially, DC fault current signals are captured from the DC bus under different operating conditions and processed through the AVMD to decompose the signals into intrinsic mode functions (IMFs). The VMD is made adaptive by minimizing the objective function of the L-kurtosis index for optimal modal number (K) and penalty factor (σ) through the improved whale optimization (IWO) algorithm. From the optimal IMFs, the most significant IMFs are chosen based on the threshold of the L-kurtosis index, and they are passed through statistical features to extract efficient data. Further, the training and testing of this data set is carried out through IBLS for obtaining the accurate detection and discrimination of DC faults. The conventional BLS method is improved through elastic net ridge regression for calculating the weights. The effectiveness of the proposed AVMD based IBLS algorithm is verified by its superiority in terms of relative computation time (RCT), classification accuracy (CA) with the confusion matrix, and their performance indices by comparing with other existing methods under different case studies. Finally, the simplicity and practicability of the proposed work are tested and implemented in the dSPACE 1104 embedded processor.

Chaotic slime mould optimization algorithm for optimal load-shedding in distribution system

• Introduces Chaotic Slime Mould Algorithm (CSMA) as an optimal load shedding scheme of islanded DG integrated systems. • A fitness function comprising of maximum amount of remaining load and voltage stability margin (VSM) is adopted. • IEEE 33 bus and IEEE 69 bus distribution systems are used to assess the algorithm’s efficacy. • The proposed CSMA algorithm is compared with Slime mould algorithm (SMA) and Backtrack search algorithm (BSA). In addition, non-parametric statistical analysis have been conducted to adequately compare the algorithms. • In terms of fitness value, time consumption, and convergence characteristics, CSMA outperforms both BSA and SMA. In addition, CSMA ensures a better voltage profile and provides a solution with the least amount of load to be shed. The critical challenge for an efficient islanding operation of a distribution system having Distributed Generation (DG) is preserving the frequency and voltage stability. Contemporary load shedding schemes are inefficient and do not adequately assess the optimum amount of load to shed which results in either excessive or inadequate load shedding. Hence, this paper presents an optimal load shedding technique using Chaotic Slime Mould Algorithm (CSMA) with sinusoidal map in order to achieve greater efficiency. A constrained function with static voltage stability margin (VSM) index and total remaining load after load shedding was applied to accomplish the evaluation. A total of three islanding scenarios of IEEE 33 bus and IEEE 69 bus radial distribution systems were used as test systems to assess the efficacy of the proposed load shedding approach using MATLAB software. To identify performance enhancements, the developed method was compared to Backtrack Search Algorithm (BSA) and the original SMA. According to the results, CSMA outperforms both BSA and SMA in terms of remaining load and voltage stability margin index values in all the test systems.

A comprehensive review on intelligent islanding detection techniques for renewable energy integrated power system

Renewable sources of energy are used extensively in the distribution grid to meet the need for growing electricity demand and to resolve the global heating crisis caused by traditional energy sources. They offer many advantages like better efficiency, power quality, and lower air pollution. One of the vital issues with these integrations is islanding condition arising due to the sudden disconnection of grid because of some abnormal situations; however, the distributed generation (DG) retains the power supply to the local loads. Thus, efficient detection of islanding and quick detachment of DG are vital to prevent failure of equipments, grid safety disruption, and risks to personnel safety. In this context, this article represents a comprehensive review of islanding issues and different islanding detection methods (IDMs) that provide a detailed assessment for filling the research gap and thereby highlights the various issues related to island detection. A broad classification of IDMs is established based on the conventional and modern techniques such as local (Active, Passive & Hybrid) and remote IDMs with their detailed illustrations including both intelligent and signal processing-based IDMs. Comparison of various IDMs based on their merits, demerits, and various performance analysis including the non-detection zone, detection time, quality factor, power quality, effect on a microgrid, implementation cost, and applicability in multi-DG system is provided. Hence, this review will provide an insight for the new researchers interested in the area highlighting the different islanding detection techniques with their relative merits and demerits.

Phaselet-Based Limited-Time $q$-Axis DC Offset Voltage Injection for Detection of Islanding of DG and Fault in a Meshed Microgrid

Rapid grid integration of inverter-interfaced distributed generators (DGs) and low-voltage ride-through capability of the smart inverter, as per IEEE 1547 standard, has made unintentional islanding detection (UID) cumbersome. Also, the feeder reconfiguration capability in meshed microgrids with multiple DGs has made the existing UID techniques ineffective. The methods have limitations in UID for small power mismatch conditions characterizing nondetection zone (NDZ). In hybrid methods for UID, a disturbance injection is continuous or for an extended period, which degrades the power quality (PQ) and creates stability issues. Hence, a decentralized closed-loop hybrid islanding detection method (HIDM) based on the indices extracted from the subcycle phaselet (passive) technique with limited-time (only for two cycles) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$q$</tex-math></inline-formula> -axis dc offset voltage injection (active) is proposed for UID of DGs. The proposed HIDM mitigates the NDZ due to the closed-loop scheme. Subcycle estimations from the phaselet technique result in quick UID and fault detection and classification process. Furthermore, the PQ issue is reduced due to the limited-time voltage injection (based only on the command from phaselet technique) in the proposed HIDM. Simulation results from the real-time digital simulator on a meshed microgrid and performance comparison with other existing methods prove the efficacy of the proposed HIDM.

An EMD and Decision Tree-Based Protection Algorithm for the Solar PV Integrated Radial Distribution System

This article presents a fault identification technique that makes use of the empirical mode decomposition of three-phase current signals of a distribution network. The current signals measured at the substation bus over a moving window are decomposed to obtain the first-level intrinsic mode function and residue. The standard deviation of the first-level residue is calculated as a fault index for each phase and compared with a threshold to detect and categorize the type of fault. A ground fault index based on the average value of the first-level residue of the neutral current is proposed to discriminate the phase-phase and phase-phase-ground faults. The proposed algorithm has been successfully tested on the IEEE 13 bus and 34 bus distribution systems in the presence of the solar photovoltaic power plant by varying the type of fault, fault incidence angle, and fault location in the presence of noise. The selectivity of the proposed algorithm has been established by testing the algorithm with nonfaulty transients such as transformer excitation and deexcitation, feeder energization and deenergization, load switching, capacitor switching, and also those associated with distributed generation (DG) penetration like islanding and tripping of DG. Subsequently, the residue-based features are fed to a decision tree to locate the faults on the distribution system. Thus, the proposed algorithm has been successful in detecting, classifying, and locating faults with DG penetration in the presence of noise within half cycle by utilizing only current signals.

Improved Reweighted Zero-Attracting Quaternion-Valued LMS Algorithm for Islanded Distributed Generation System at IM Load

Sudden start of an IM load and frequent change of nonlinear load in a standalone distributed generation system (DGS) cause the dip in ac voltage and frequency. Moreover, these loads distort DGS currents. Therefore, in this paper, an improved-reweighted zero-attracting quaternion-valued least mean square (I-RZA-LMS)-algorithm-based voltage source converter (VSG) control is proposed for voltage and frequency regulation, and power quality improvement in DGS. Moreover, the control algorithm of dc–dc bidirectional converter (BDC) is used for dc link voltage regulation and MPPT of the solar photovoltaic array at IM starting and nonlinear loading. In this DGS, the I-RZA-LMS-based control algorithm estimates the active and reactive component currents of distorted load currents for effective harmonics mitigation, reactive power compensation, and point of common coupling voltages regulation. The proposed control algorithm rejects the dc-offset component from load currents and gives the fundamental load component. The dc link voltage of VSC is regulated using BDC with a solar feedforward term, which is used to enhance the capability of dc link voltage control under solar power variation, IM starting, and unbalanced loading. The effectiveness of the proposed DGS is validated through the simulation as well as experimental results obtained on a developed prototype of DGS.

Long-Term Impact Evaluation of Advanced Under Frequency Load Shedding Schemes on Distribution Systems With DG Islanded Operation

This paper presents a long-term impact evaluation algorithm to assess advanced under frequency load shedding (UFLS) schemes on distribution systems with intentional islanding of distributed generation (DG). The algorithm is based on a combined discrete-continuous simulation model which is utilized to verify the effect of the schemes on reliability indices such as the system average interruption frequency index, system average interruption duration index, and energy not supplied. Moreover, a polynomial neural network-based approach to advanced load shedding is implemented to support DG islanding in order to illustrate the applicability of the evaluation. Simulation results highlight the long-term effect of employing UFLS to support intentional islanding of DG using an actual network from the South of Brazil.

Matheuristic for emergency response in the electric distribution system with unforeseen islanding

Since power supply may suffer interruptions, caused by climate events or even due to equipment and human failures, these interruptions are associated with procedures commonly referred as emergency orders. These emergency orders must be attended by repair crews in an attempt to reestablish the power supply all over the system. Assuming a set of these emergency orders, the network operation center (NOC) must find a scheduling so that they are all attended by the repair crews and the power supply reestablished as soon as possible, while considering the minimization of the total service cost. Distributed generation (DG) may be one alternative for furnishing temporally power supply, such as photovoltaic and wind power generation sources. In such approach, the islanding operation confers such a complexity when considering how much time should be needed to supply the affected loads and which ones may be even selected. This study proposes a novel matheuristic for emergency response to the contingency planning problem related to electric distribution operations, considering unforeseen islanding of DG. From using a mixed integer linear programming (MILP) model, based on the emergency order scheduling problem (EOSP) with islanding operation formulations, the optimization criteria involves the minimization of the cost of non-supplied energy and the penalties related to high important customers, while respecting electrical constraints. Computational results on the IEEE 33-bus system, modified with the insertion of DGs, show the effectiveness of the proposed solution on reducing the total attendance cost when compared to a traditional scheduling solution without considering the islanding operation.

Active Islanding Detection Technique for Distributed Generation

Islanding detection plays a very important role in the design of a protection system for distributed generation (DG). The conventional methods face problems during the perfectly matched balanced load condition of DG as there is no significant change in voltage and frequency. In this paper, an active islanding detection method is proposed which perturbs the DC link voltage of DG, actuated when there is a sudden rise in the total harmonic distortion (THD) of the system greater than 4%. This perturbation again increases the level of harmonics if the DG is islanded as the grid loses control over DG. Thus, the increase in harmonic level is utilized as an indication of islanding. During normal mode, the grid offers a low-impedance path to harmonics and, thus, the harmonic level is maintained. The testing of islanding is done with the help of a MATLAB model of grid-connected DFIG-based wind farm. The proposed method can be a potential method for detecting islanding of inverter-based DGs during worst cases and also for knowing the mode of operation of DG, when implementing adaptive protection.

𝕃1 adaptive networked controller for islanded distributed generation systems in a microgrid

ABSTRACTIn this paper, we implement an output-feedback adaptive controller for islanded distributed generation systems (DGs) with communication, load and generation constraints. The adaptive controller is introduced to deal with nonlinearities of dynamical systems and unknown constraints. It primarily consists of a predictor, an adaptive law, and a control law. Herein, the controller can sustain desired performance and the robustness, in which the control law loop contains a low pass filter that sustain a rapid adaptation rate without fluctuations. The critical challenge into a standalone microgrid is to coordinate the necessitate load power with the distributed generations production in the presence of load/generation fluctuations. The coordinated controller is implemented to undertake the conflicts, and to enhance the performance, and to minimise the control cost by coordinate the requirements between decentralised controllers. The proposed controller is worthy for ensuring the network stability of DGs in a microgrid environment in the presence of uncertainties and transmission time delays. A typical simulation example is presented to confirm the effectiveness of the proposed design procedure.

A new controlled superconducting magnetic energy storage for dynamic stabilization of distributed generation in islanding mode of operation

Summary According to IEEE std. 1547, islanding mode is “a condition in which a portion of an Electric Power System (EPS) is energized solely by one or more local EPSs through the associated Point of Common Coupling (PCC) while that portion is electrically separated from the rest of the area EPS”. Therefore, the dynamic instability due to islanding may result in power swing and finally loss of synchronism. Hence, many studies have been done for islanding detection and disconnection of distributed generation (DG) in an EPS. But, these conventional methods eventually lead to the disconnection of the DG units. To improve DG dynamic stability, superconducting magnetic energy storage (SMES) can be used effectively, because SMES have a high-energy density and fast response. This paper proposes a new method to damp the power swing after DG islanding and to maintain synchronism conditions based on SMES. Hence, the disconnection of the DG units is not required. Also, new controllers are developed for SMES including voltage source converter (VSC), and DC-DC chopper. The controller structures of VSC and DC-DC chopper are of PI and fuzzy logic-based type, respectively. Superconducting coil charging is controlled by the DC-DC chopper. SMES sizing is performed, based on power swing equations. Hereupon, dynamic load model is considered. Performance of the proposed method is evaluated by defining 12 scenarios such as strong and weak networks with load changing simulated in PSCAD. Simulation results show that the islanded DG stabilization (IDGS) method has good performance to maintain stability margin in a weak network.

A Novel Hybrid Islanding Detection Method for Inverter-Based DGs Using SFS and ROCOF

This paper is aimed at proposing a new hybrid method for the islanding detection of distributed-generation (DG) units. Hybrid method operation is based on the combination of an active and a passive method, for which the optimized Sandia frequency shift (SFS) method is used as the selected active method, and rate of change of frequency relay (ROCOF) is used as the passive method. In order to demonstrate the effectiveness of the proposed technique on islanding detection, several simulation studies based on IEEE 1547 and UL1741 anti-islanding test requirements are carried out. The evaluation of simulation results reveals that the control system, based on the proposed hybrid algorithm, meets the DG islanding protection requirements efficiently. Moreover, it will be demonstrated that the proposed hybrid method is capable of accurately operating under multiple DG units, load switching in the grid-connected mode, as well as different load quality factor conditions.

Distributed Generation Islanding Effect on Distribution Networks and End User Loads Using the Master-Slave Islanding Method

This study aims to address the feasibility of planned islanding operation and to investigate the effect of unplanned islanding using the master-slave islanding method for controlling the distributed generation units during grid-connected and islanding operation. Neplan desktop power simulation tool was used for the modelling and simulation of a realistic MV network with four different distributed generation technologies (diesel, gas, hydro and wind) along with their excitation and governor control systems, while an exponential model was used to represent the loads in the network. The dynamic and steady state behavior of the four distributed generation technologies were investigated during grid-connected operation and two transition modes to the islanding situation, planned and unplanned. The obtained results that validated through various case studies have shown that a suitable planned islanding transition could provide support to critical loads at the event of electricity utility outages.

A Decentralized Multiagent System Approach for Service Restoration Using DG Islanding

This paper proposes a decentralized multiagent system (MAS) approach for service restoration using controlled distributed generator (DG) islanding. Furthermore, it investigates the impacts of vehicle-to-grid (V2G) facility of the electric vehicles (EVs) for service restoration. Service restoration is formulated as a multiobjective optimization problem considering maximization of priority load restored and minimization of switching operations as the multiple objectives and solved using the proposed decentralized MAS approach. Extensive case studies are conducted on 38, 69, and 119 bus distribution systems, and the following advantages of the proposed MAS approach are observed: 1) flexibility—to perform under different DG and EV penetration levels; 2) scalability—to restore service for different size test systems, small as well as large; and 3) robustness—ability to perform efficiently for both single as well as multiple-fault situations. The simulation results also highlight the benefits of V2G feature of EVs for service restoration.

A sequence perturbation based islanding detection for distributed generation with periodic code matching

Islanding detection is a significant technical barrier to the distributed generation (DG) industry. When islanding occurs, the inverter current of DG has a strong correlation with load voltage of DG. With respect to the correlation, this paper proposes an islanding detection method (IDM) based on periodic matching of the sequence perturbation. In this periodic code matching detection method, a periodic sequence is introduced to perturb the inverter current amplitude. The IDM can be achieved by calculating periodic matching degree between the islanding detection coefficient and the sequence. The influence on IDM imposed by sequence characteristics and load variation is also discussed in this paper. According to IEEE Std. 1547, an islanding detection model is designed and simulated in this paper. The simulation and experiment results indicate a strong ability to anti-harmonic noise when the 1-0 non-zeroing sequence with six bits is selected as the perturbation sequence. The proposed method introduces little damage to grid. In the normal range of voltage and frequency, this method can detect the islanding of DG reliably and effectively even if load varies.

A combined method to efficiently adjust frequency-based anti-islanding relays of synchronous distributed generation

An important requirement for interconnecting distributed generation is anti-islanding protection. This paper uses the capabilities of two methods, application region (AR) and power imbalance AR, to efficiently adjust frequency-based relays. The proposed method gives a proper simple and nonexpensive solution to the synchronous distributed generation islanding detection problem. It employs the common protection devices: frequency or rate of change of frequency relays. These relays are adjusted in order to satisfy the anti-islanding protection and safe and abnormal frequency variation requirements and also to discriminate between islanding and nonislanding disturbances. The procedure is applied to a real system, which is a portion of the Isfahan Regional Electric Network in Iran, to show the effectiveness of the proposed approach. Copyright © 2014 John Wiley & Sons, Ltd.

The Analysis of the Performance of Active Frequency Drift Islanding Method

Active frequency drift islanding detection method is one of most widely used in the distributed generator islanding detection. Now domestic researches of islanding detection have not been done deep researched about the reason why islanding detection method will become invalid. Therefore, the paper analyses the performances of the frequency drift islanding method from load phase frequency characteristic and algorithm phase frequency characteristic, which are the major factors affecting the effectiveness of islanding detection method. At last, this paper proved the analysis results with MATLAB.

Analysis, Design, and Experimental Verification of a Synchronous Reference Frame Voltage Control for Single-Phase Inverters

Control of three-phase power converters in the synchronous reference frame (SRF) is now a mature and well-developed research topic. However, for single-phase converters, it is not as well established as three-phase applications. This paper deals with the design of an SRF multiloop control strategy for single-phase inverter-based islanded distributed generation systems. The proposed controller uses an SRF proportional-integral controller to regulate the instantaneous output voltage, a capacitor current shaping loop in the stationary reference frame to provide active damping and improve both transient and steady-state performances, a voltage decoupling feedforward to improve the system robustness, and a multiresonant harmonic compensator to prevent low-order load current harmonics to distort the inverter output voltage. Since the voltage loop works in the SRF, it is not straightforward to fine tune the control parameters and evaluate the stability of the whole closed-loop system. To overcome this problem, the stationary reference frame equivalent of the voltage loop is derived. Then, a step-by-step systematic design procedure based on a frequency response approach is presented. Finally, the theoretical achievements are supported by experimental results.

New algorithm based on CLPSO for controlled islanding of distribution systems

Controlled islanding operation of distribution systems having significant penetration of distributed generation (DG) is becoming an important option for economical and technical reasons. Implementation of intentional islanding of DG improves the continuity of supply and reliability of power system. In this paper, comprehensive learning particle swarm optimization (CLPSO) is used to optimally partition the distribution system in case of main upstream loss. The objective is to find the optimal islanding scheme of distribution system to achieve minimum active power generation cost, minimum reactive generation cost and minimum cost of the un-served power while satisfying system operational constraints. The solution proceeds by splitting the system into islands after the loss of main upstream feeder. In each island, the power balanced is achieved through load shedding. An optimal dispatch of the generating units of each island is then carried out to achieve minimum active power generation cost. A power flow calculations are carried out to calculate the reactive power generated by each unit and to check the operational constraints of the system. Finally, the effects of controlled islanding with and without utility owned DGs on the system reliability indices is studied. The proposed algorithm is applied to two radial and meshed test systems.

Time-frequency transform-based islanding detection in distributed generation

This study presents a new technique for islanding detection in distributed generation (DG) using time-frequency transform such as S-transform. S-transform is an invertible time-frequency spectral localisation technique that provides the time-frequency contours of the voltage and current signals retrieved at the target DG location. The energy index (ratio of the spectral energy content of the voltage to current signals) is computed to track the islanding situation from non-islanding conditions such as sudden load change, tripping of other DG, etc. Further, to aid the islanding detection scheme, a cumulative sum detector is also computed based on the spectral energy content of the negative sequence components of the current and voltage signals. The results, based on extensive study, indicate that the proposed technique can reliably detect islanding in DGs connected to power distribution network.