Deploying grid ancillary services through distributed energy resources (DERs) challenges islanding detection techniques (IDTs). Power regulations, for instance, may mitigate power mismatches in islanded microgrids, increasing the risk of undetected islands. Additionally, when the grid is connected, false islanding detection during low-voltage events can disrupt low-voltage ride-through (LVRT) operations. Existing IDTs that comply with these services and requirements often suffer from power quality degradation and limited scalability in multi-inverter systems. To address these gaps, this study proposes an active IDT using the DER's input admittance shaping within a narrow negative-sequence frequency band. The shaped admittance results in a negligible negative-sequence disturbance (NSD) injection during grid-connected operation while ensuring rapid and synchronized NSD jump after island formation in multi-inverter systems. Thus, islanding is detected when the rate of change of negative-sequence voltage at the DER terminal exceeds a preset threshold within a specified timeframe. Importantly, the proposed IDT does not affect the positive sequence component, avoiding conflict with ancillary services in grid-connected operations. Numerous simulations are conducted in PSCAD-EMTDC in accordance with the IEEE Std. 1547.1-2020 test procedure. The results demonstrate precise and rapid islanding detection in single- and multi-inverter scenarios, including zero/small power mismatches with DER's power regulations. In addition, the proposed IDT does not exhibit false tripping during low-voltage events, complying with LVRT requirements.

Effective islanding detection is mandatory for distributed generations (DGs) to avoid equipment damage and ensure the safety of network personnel. This paper proposes a fast, accurate, power quality-friendly, and practical two-stage active power curtailment (APC)-based islanding detection technique (IDT) for photovoltaic (PV)-rich microgrids. In the first stage, a periodic small disturbance is injected into the maximum power point tracking (MPPT) algorithm to slightly curtail the DG's active power, causing a small mismatch even on a balanced island. During islanding, the introduced active power mismatch shifts output voltage, triggering the second stage disturbance to the MPPT algorithm. Hence, the output voltage drops further, resulting in islanding detection. A real-time digital simulation (RTDS) using the modified IEEE 13-node system corroborates the successful detection of all stringent cases in less than 1.2 s with no false tripping for non-islanding disturbances. This zero non-detection zone (NDZ) is achieved by curtailing less than 1 % of the DG's available output. This technique is a practical solution for microgrids with high penetration of photovoltaic generators (PVGs) due to its simple structure and straightforward threshold determination, irrespective of the microgrid structure. The fast detection time allows the DG to seamlessly transition to the standalone microgrid.

In recent years, grid-connected photovoltaic system (GCPVS) has been installed at a steady pace around the world due to its clean energy generation, simple operation, and low maintenance. This technology is also a convenient solution for peak shaving in residential and commercial buildings of arid areas with great air conditioning demand in the summer noon. Several supportive policies have been accordingly legalized by countries/regions to attract private and government-based stakeholders. This paper proposes a techno-economic assessment of GCPVS in arid areas from the peak shaving perspective. As a practical case, the effect of a commissioned 102 kW GCPVS on peak shaving of the Mashhad waste management organization building is assessed, exploiting high-resolution one-year recorded data. The results endorse that installed GCPVS shaves the peak demand of this commercial building in summer noon by 40–50% on average. An economic evaluation is also conducted; the outputs highlighted that this project is economically viable with a 43,671 € net present value (NPV) and 34.5% internal rate of return (IRR). It is finally recommended that such practical and reliable studies with a large range of applications provide valuable insights and recommendations to the policymakers to adopt a well-modified policy according to the local economic and solar potential.

This paper introduces a novel detailed formulation for analytically determining the maximum power point (MPP) of a photovoltaic (PV) module. The approach involves an analytical approximation of a 4-parameter PV model, taking into account the series resistance, which serves as the initial value for the fixed-point method to enhance accuracy. Additionally, the paper includes a statistical analysis of convergence to highlight the method’s limitations. The performance of the proposed method is evaluated against actual measurements of over one hundred thousand current-voltage (I-V) characteristic curves from eight different PV modules, as reported by the National Renewable Energy Laboratory (NREL), and is also compared with two existing literature approximations. Furthermore, a sensitivity analysis of the solution error under varying irradiance and temperature conditions is conducted. The method demonstrates high accuracy for engineering applications.

Wavelet transform has proven to be a capable tool for protection purposes in high voltage direct current (HVDC) transmission lines due to its desired speed and accuracy. However, the need to enhance the WT-based protection methods in terms of sensitivity and selectivity is of interest. This paper proposes a new non-unit WT-based protection method with adaptive threshold setting. According to the improved time-domain analytical approach, line-mode fault-generated voltage traveling wave is adopted to identify the internal faults. The simulation results for a multi-terminal modular multilevel converter-based HVDC grid in PSCAD/EMTDC corroborate accurate and fast internal faults detection of the proposed method, up to 850 Ω, i.e., almost three times larger than conventional schemes. In addition, the reliable performance of the presented method in a noisy environment, using relatively low sampling frequencies, and different sizes of current limiting inductors is demonstrated in the presented analysis. The generality of the presented analytical approach ensures that the proposed protection method can be extended to more complex HVDC grids.

Overvoltage instability is a growing concern in a standalone low-voltage (LV) microgrid (MG) with non-dispatchable intermittent renewable energies such as residential and commercial photovoltaic generators (PVGs). Several overvoltage controllers used in PV arrays have adopted the concept of standard deviation from the maximum power point (MPP) to curtail the generated power. However, these solutions lack presenting analytical expression for the MPP deviation size, settings tuning independent of the MG's/PV's characteristics, scalability, and accurate power-sharing in the same control structure. To overcome these limitations, this paper proposes a new analytical MPP tracking (MPPT)-based overvoltage and power-sharing control method using the series equivalent resistance of the PV module model. By applying this analytical expression, the size of the PV array voltage shift to the right-hand side of the MPP is obtained in terms of overvoltage level, while all PVGs proportionally curtail the active power output. The effectiveness of the proposed methodology is shown in various low-demand and high-PV generation cases through a real time digital simulator (RTDS) platform. In addition to the fast and accurate performance, the presented method benefits from the straightforward and communication-free structure as it solely exploits the point of common coupling (PCC) voltage. Also, the method's threshold does not require re- tuning after MG restructure, ensuring scalability. Without relying on other microgrid facilities, the proposed methodology is accordingly an effective solution for practical PV-based LV MGs.

This paper proposes a fast and reliable hybrid islanding detection method (IDM) for mini-hydro-based distributed generations (DGs) with zero non-detection zone (NDZ). The proposed IDM aims to tackle the islanding events caused by a self-excited induction generator (SEIG) when it is driven by a mini-hydro turbine system utilising the transient dynamic response of the governor for the first time. To achieve such a goal, it takes advantage of a two-stage process in which both passive and active techniques are combined. Thus, if the rate of change of frequency (ROCOF)-based threshold of the first stage is exceeded, the power reference of the mini-hydro unit is modified, implying a change in the turbine governor gate position. The mechanical torque applied to the prime mover is accordingly shifted to a new state so that both frequency and its derivative will exceed the established thresholds in the second stage in the islanding mode. Conversely, the effect of imposed disturbance is eminently negligible in the grid-connected mode since the frequency is strictly dictated by the main grid. The proposed IDM has been evaluated through numerous islanding and non-islanding case studies considering both single and multi-DG scenarios in MATLAB/Simulink. The outcomes highlight the outstanding performance of the proposed algorithm with zero NDZ and 473 ms average detection time, indicating the capability of the governor system as a reliable tool to identify islanding operations. The proposed technique does not degrade the power quality (PQ) of the grid, requires a low level of computational complexity and provides a high degree of reliability. Therefore, it is a robust and cost-effective solution for future microgrids with great penetration of mini-hydro units.

The connection of renewable energy sources (RESs) to the distribution network has been rising at a steady pace over the past decades. The great penetration of RESs such as grid-connected photovoltaic system brings new technical challenges to the distribution networks such as unintentional islanding. Conceptually, this situation occurs when a portion of the network that has been isolated from the main grid remains energised by the embedded RESs. This unexpected scenario should be thereby identified effectively to avoid frequency and voltage deviations and their hazardous effects. The aim of this paper is to provide a comprehensive review on the recently developed islanding detection methods for grid-following/grid-connected photovoltaic system, analyse their existing limitations, and suggest possible future research implementations. In this context, an in-depth comparison is provided considering the main features used in islanding detection methods such as non-detection zone, detection time, implementation cost and complexity, and power quality degradation. Finally, the main technical requirements established by the current grid codes are recalled identifying potential multi-functional approaches to expand the current islanding detection capabilities.

Due to a 15% electricity shortage in Iran, the scheduled shutdown occurs frequently in summer noon in 2021. These power cuts lead to serious social and economic effects on both private and government sectors. As a solution, Mashhad Electric Energy Distribution Company extended the current FiT11Feed-in-tariff (FiT) framework in a way that any individual can upgrade its existing GCPVS22Grid-connected photovoltaic system (GCPVS) to the hybrid one through exploiting BESS33Battery energy storage system (BESS) and substituting the grid-tie inverter with a hybrid one. When the grid is present, the investor sells the whole generated energy at a guaranteed price. Further, he/she benefits continuous supply of energy for domestic loads during the grid power cut. This paper presents the economic evaluation of the residential hybrid PV-BESS under FiT policy in Mashhad as a case study. The BESS is initially designed for a traditional residential demand taking the frequency and duration of the power cuts into account. Afterwards, the hybrid system is assessed under the current FiT policy from the economic perspective. The presented analyzes endorse that although the initial cost of the hybrid system raises with respect to the grid-connected type, this project with 463,425,280 Iranian Rials NPV44Net present value (NPV), 12.68 PBT55Payback period time (PBT), and 28.3% IRR 66Internal rate of return (IRR) is economically viable under the current FiT policy.

Currently, the economy of Middle Eastern countries relies heavily on fossil fuel sources. The direct and indirect adverse consequences of fossil fuel utilization for power generation enforce the region’s countries to raise the share of renewable energy. In this context, various incentive policies have been developed to encourage the residential and industrial sectors to support a portion of energy needs through renewable energy resources. In this case, a solar water heating system (SWHS) as an application of solar thermal technology provides some of the heat energy requirements for domestic hot water (DHW) and space heating, supported conventionally by electricity or natural gas, or even other fossil fuels. This paper reviews the feasibility of the SWHS in the Middle East region from technical and economical standpoints and investigates some of the progress, challenges, and barriers toward this market. The pay-back times and CO₂ emission reduction under different incentive frameworks and configurations of each system have been assessed in this context. Furthermore, the advantages and weaknesses of the SWHS in several countries have been reported. Finally, various guidelines have been proposed to enhance the development of this technology.

This study proposes a fast and precise voltage feedback-based islanding detection method (IDM) for grid-connected photovoltaic systems (GCPVSs) based microgrid. In this algorithm, a disturbance containing the absolute deviation of the output voltage is injected into the inverter's d-axis reference current which tunes the active power output. In islanded mode, the applied disturbance reduces the active power output and consequently point of common coupling voltage beyond the standard setting while its effect at the presence of the grid is negligible. The assessment of the proposed IDM has been conducted in the MATLAB/Simulink platform under extensive scenarios defined by IEEE 1547-2008 and UL 1741 standards for a case study system with two large-scale GCPVSs. The provided outputs remark accurate islanding classification in all cases within 810ms, much lower than the maximum permissible time postulated in islanding standards. This time is short enough to restore GCPVS for autonomous operation of microgrid as well. The comparative analysis of the proposed strategy with a few existing IDMs confirmed its overall superiorities in the terms of non-detection zone, detection time, being applicable into the microgrid, simple threshold determination, and straightforward and cost-effective implementation.

This paper investigates the economic viability of a commercial grid-connected photovoltaic system (GCPVS) in the Middle East region. In this regard, an economic assessment of a 120 kW_p GCPVS connected in December 2017 under a feed-in tariff (FiT) scheme in Iran—the leading country in the region establishing a supportive policy—is carried out. In this plan, private enterprises can install GCPVS and sell whole generated energy at a high guaranteed price for twenty years. Several economic indices, including net present value (NPV), internal rate of return (IRR), benefit-cost ratio (BCR), payback period time (PBT), and levelized cost of energy (LCOE) are determined to unveil the effectiveness of the enacted program. This paper exploits one-year recorded energy data of this commercial system to boost the reliability of the results. Moreover, PV module degradation factor is taken into account to make the analysis as realistic as possible. The computed outputs imply that this commercial system, with 3.36 BCR, 31.88% IRR, 5.24 years PBT, and 0.0477 $/kWh LCOE, is highly appealing. The sensitivity analysis also highlight that the profitability of the GCPVS investment is secure under a wide range of unpredictable parameters. It is shown for instance that the PBT and IRR are deteriorated by 5.48% and 1.50 years, while the generated energy lowers by 20% compared with the predicted value for the upcoming years. Having said that, it is still far away from the infeasible condition. A comparative analysis between the current findings and similar researches endorse the Middle East region as the highest potential site for PV installation. It is finally deduced that a properly modified FiT scheme can be set in the region's countries concerning the local meteorological and economic conditions to stimulate the investment of this technology.

This article proposes a fast and reliable two-level islanding detection method (IDM) for grid-connected photovoltaic system (GCPVS)-based microgrid. In the first level of the proposed IDM, the magnitude of the rate of change of output voltage (ROCOV) is computed. If this variable exceeds a predefined threshold, a disturbance is injected into the duty cycle of DC/DC converter after a given time delay to deviate the system operating point away of its maximum power point (MPP) condition. This leads to a substantial active power output and voltage reduction in an islanded mode. Therefore, the ROCOV and the rate of change of active power output (ROCOP) indices, measured in the second stage, pose great negative sets at the same time in islanding states. However, the variation of at least one of these variables is near-zero in non-islanding switching events. The assessment of the presented algorithm has been conducted under extensive islanding and non-islanding scenarios for a case study system with two PV power plants using hardware-in-the-loop (HiL) simulation tests. The provided results remark precise islanding classification with an eminently small non-detection zone (NDZ) within 510 ms. The presented IDM has the advantages of self-standing thresholds determination, no improper effect on the output power quality, and simple and inexpensive structure. Moreover, the fast MPP restoration of the proposed scheme after islanding identification boosts the chance of seamless reconnection and DG autonomous operation in microgrid.

This paper proposes a novel islanding detection method (IDM) for grid-connected photovoltaic systems (GCPVSs) through a disturbance injection in the maximum power point tracking (MPPT) algorithm. When an absolute deviation of the output voltage exceeds a threshold, the applied disturbance shifts system operating point from its maximum power point (MPP) condition. This leads to a sharp active power output reduction and consequently, a significant voltage drop in islanded mode beyond the standard voltage limit. The proposed algorithm is defined in a way that the distributed generator (DG) can be restored to MPP after islanding classification. It is thereby effective in microgrid in where the power injection at maximum level to cater the critical loads and maintain the stability of the isolated area are pursued. An intentional time delay has also been considered to avoid nuisance tripping in short-circuit faults which do not require tripping. The assessment of the proposed technique has been conducted for a sample network containing two GCPVSs in a real-time platform including actual relays in hardware-in-the-loop (HiL). The provided results under extensive islanding scenarios defined in islanding standards endorse timely and accurately detection with negligible non-detection zone (NDZ) as well as no false tripping in non-islanding disturbances. The comparative analysis of the presented scheme with a few recent IDMs for GCPVS highlights its overall superiorities, including very small NDZ, fast detection, thresholds self-standing determination, no adverse effect on power quality, and simple and inexpensive integration.