Grid-connected Distributed Generation Research Articles

Islanding Event Detection in Grid-Connected Distributed Generation Systems Using Unscented Kalman Filter

A pressing concern in modern smart grid systems revolves around islanding, leading to unpredictable system parameters and a decline in power quality. In response to this concern, we introduce a novel passive method for identifying islanding in grid-connected distributed generation units. This method utilizes the unscented Kalman filter (UKF) to assess the voltage signal captured at the DG position. The triphase voltage signal observed at the point of common coupling (PCC) is used as the test signal. The UKF extracts and filters the harmonic content of the voltage signal to produce a residual signal, which detects changes in the power system. The estimation of total harmonic distortion (THD) follows, and its fluctuations help discern between islanding and typical events. This suggested approach undergoes assessment through a test system simulated in MATLAB/Simulink across different situations. Outcome findings underscore the efficacy of the suggested approach in distinguishing between islanding and regular occurrences, ensuring enhanced reliability and resilience against incorrect operations by removing the zone of nondetection. In our detailed experiments, we found that the proposed unscented Kalman filter (UKF) technique improved islanding detection accuracy by approximately 90% over traditional methods, under varied conditions. Specifically, the nondetection zone (NDZ) was reduced by 95% when compared to the most commonly used passive methods. Furthermore, in scenarios with high harmonic content and noise, the UKF showcased a 90% improvement in reliability over conventional techniques.

Research on Optimal Configuration of Distributed Generation based on Multi-scenario Analysis

In order to make the grid-connected planning of distributed generation more reasonable, the uncertainties of intermittent distributed generation output and load forecasting are included in the solution process. Firstly, multi-scenario analysis is introduced to transform the source load uncertainty problem into deterministic problem, and the Latin super-force sampling method is used to generate the initial planning scene. The density peak clustering idea and elbow method are used to improve the K-means clustering algorithm and reduce the scene. Secondly, the optimal allocation model of grid-connected distributed generation is constructed with the minimum annual comprehensive cost as the objective function. Finally, in view of the slow convergence speed and easy to fall into local optimum of particle swarm optimization (PSO), an adaptive inertia weight factor is adopted to improve PSO, and the effectiveness of the proposed model and method is verified by IEEE 33-node standard simulation example.

A New Current Limiting Strategy Based on Id − ω and Iq − V Droop Characteristics for Grid-Connected Distributed Generations

Background: Increase in the output current of inverter-based Distributed Generations (DGs), which are connected to Upstream Grid (UG) and equipped with droop controller, due to UG frequency and/or voltage magnitude drop is a conventional event. The first solution to limit the output currents is using current limiter circuits at the output side of the grid-connected droop-controlled DG. Suppose the increasing output currents of this DG in continuous UG frequency drop exceeds their maximum. In that case, the current limiter circuits limit them to their maximum values. This limitation is based on the P-ω droop characteristic due to instability because the DG frequency will be greater than the UG frequency. This difference leads to sending and receiving power between DG and UG. To overcome this problem, different methods have been presented in the literature. Methods: This paper proposes a method based on a floating droop controller. In this method in order to limit output currents strictly, I_od-ω and I_oq-v droop characteristics are used instead of P-ω and Q-v characteristics, respectively. In the proposed method, instead of increasing the droop coefficients to limit currents, the droop curves are moved downward. Also, two transient supplementary signals are proposed to ensure that instantaneous currents do not have overshoot in the transient state. Results: Small-signal stability analysis shows that the system remains stable under the proposed controller. Moreover, the proposed strategy performance is indicated by time-domain simulation results using MATLAB/Simulink software under different case studies. Conclusion: The proposed new method limits the output currents of grid-connected droop-controlled DG without using current limiter circuits and performs a stable operation under the abnormal conditions of the grid.

Performance Analysis of a PEMFC-Based Grid-Connected Distributed Generation System

Less energy consumption and more efficient use of renewables are among the sustainable energy targets of modern societies. The essential activities to be achieved under these objectives are to increase distributed generation (DG) structures’ applicability. DG systems are small-scale versions of the traditional power grid; they are supported by micro turbines, photovoltaics (PV) modules, hydrogen fuel cells, wind turbines, combined heat and power systems, and energy storage units. The aim of this research is to detail the performance analysis of a proton-exchange membrane fuel cell (PEMFC)-based grid-connected distributed generation system with the help of empirical calculations. To this end, we aimed to establish the system and analyze the performance of the reliable operation of the system with experimental verifications. The findings demonstrate how much power can be generated annually, through real meteorological data, to dispatch to constantly variable loads. While 53.56% of the total energy demand is met by the utility grid, 46.44% of the demand is met by the produced energy i.e., from the DG. The PEMFC-based DG system analyzed in detail in this study was located at Marmara University. According to the results of the performance analysis, significant points of this study will be highlighted to assist the researchers working in this field. Our results are encouraging and can be certified by a larger sample size with neat weather conditions in terms of the percentage of procurement of energy.

Research on grid-connected distributed generation considering relay protection

The access of distributed generation can cause some impacts on the distribution network, especially the change of the magnitude and direction of the short-circuit current may cause the relay protection device in the system to refuse or malfunction. Aiming at this problem, a mathematical model id founded in this paper, whose target is the maximum capacity of distributed generation. Besides normal constraints such as the node voltage and the total capacity, the current protection constraint is also taken into account. The genetic algorithm is used to optimize the capacity and location of the distributed generation in the IEEE33 bus distribution system model, and the obtained results verify the importance of taking into account the relay protection constraint.

Performance of a new hybrid approach for detection of islanding for inverter-based DGs

This paper proposes a new hybrid method for islanding detection and minimizes the Non-Detection Zone (NDZ), for an inverter-based grid-connected distributed generation (DG) system. The proposed hybrid method is an integration of the modified active Sandia Frequency Shift (SFS) method and the passive reactive power variation technique. The modified active SFS method is obtained by adaptive tuning of the gain parameter Ksfs, using the Adaptive Particle Swarm Optimization (APSO) technique. The proposed hybrid method produces a significant reduction of NDZ and is suitable for more accurate detection of islanding condition. The effect of NDZ for the proposed hybrid method has been derived analytically and the system performance has been assessed, under various power mismatch conditions for a DG-grid interface. The overall system performance has been found to be superior under the presence of constant power control strategy. The effect of frequency and voltage variations at the common coupling point during islanding have also been considered. Finally, the performance of the proposed method under the IEEE standard 1547 islanding test condition has been investigated for different load factors and load variations.

The role of residential distributed energy resources in Pakistan's energy transition

In light of climate change concerns and falling costs, many low-income countries, such as Pakistan, have adopted a number of policies to incentivise distributed energy resources and generation. These policies have meant that the installed base of grid-connected distributed solar generation in Pakistan has grown rapidly, from only 1 MW in 2015–2016 to 232 MW in 2020–2021. However, it still constitutes a paltry 0.5% of the overall electricity mix. In this paper, using high-resolution demand and generation profiles from Lahore (the second most populous city in Pakistan and the one with the most distributed generation), we show that distributed generation offers low payback periods for urban households, even without net metering. This calculus is aided by likely future tariff hikes. Additionally, distributed generation helps support the grid, even without storage or demand response, due to a close alignment between supply and demand. Based on this analysis, we recommend the regulator to provide longer term visibility on the continuation of incentives such as net metering, and how this will eventually be shifted towards solar mandates. Likewise, it is prudent for distribution companies to provide targeted incentives for uptake of distributed generation to alleviate issues such as non-technical losses and transformer overloading.

Voltage Rise Problem in Distribution Networks with Distributed Generation: A Review of Technologies, Impact and Mitigation Approaches

Energy demand has constantly been on the rise due to aggressive industrialization and civilization. This rise in energy demand results in the massive penetration of distributed generation (DG) in the distribution network (DN) which has been a holistic approach to enhance the capacity of distribution networks. However, this has led to a number of issues in the low voltage network, one of which is the voltage rise problem. This happens when generation exceeds demand thereby causing reverse power flow and consequently leading to overvoltage. A number of methods have been discussed in the literature to overcome this challenge ranging from network augmentation to active management of the distribution networks. This paper discusses the issue of voltage rise problem and its impact on distribution networks with high amounts of distributed energy resources (DERs). It presents different DG technologies such as those based on conventional and unconventional resources and other DERs such as battery storage systems and fuel cells. The study provides a comprehensive overview of approaches employed to curtail the issue of voltage increase at the point of common coupling (PCC), which includes strategies based on the network reinforcement methodology and the active distribution network management. A techno-economic comparison is then introduced in the paper to ascertain the similarities and dissimilarities of different mitigation approaches based on the technology involved, ease of deployment, cost implication, and their pros and cons. The paper provides insights into directions for future research in mitigating the impact of voltage rise presented by grid-connected DGs without limiting their increased penetration in the existing power grid.

Grid – connected operation and performance of hybrid DG having PV and PEMFC

Purpose“the purpose of this study/paper” or “this study/paper aims to” in the Purpose section of the . The integration of distributed generation (DG) to the utility grid is yet another approach to provide reliable and secured power.Design/methodology/approachThe significant concern in this contemporary world are the day-to-day increasing power demand, lack of energy and increasing environmental pollution, which are threatening the existence of living things.FindingsThe research focus here is to adequacy and security in the grid-integrated hybrid distributed generation (DG) having photovoltaic (PV) and proton exchange membrane fuel cell.Originality/valuePV system is a clean source of generation and suitable for many applications. Photovoltaic cell captures the energy from solar irradiation. To track the maximum power from PV, perturb and observe method is used. As it is intermittent in nature, integrating PV with fuel cell makes the hybrid source more reliable. Power electronic interfacing devices are used to integrate this hybrid DG source to microgrid. The simulation of this grid-connected hybrid DG is performed using Matlab/Simulink environment.

Intelligent Transition Control between Grid-Connected and Standalone Modes of Three-Phase Grid-Integrated Distributed Generation Systems

This paper proposes an intelligent seamless transition controller for smooth transition between grid-connected (GC) and standalone modes of distributed generation (DG) units in the grid. The development of this seamless controller contributes to two main processes in the transition modes: the synchronization process and an islanding process. For the synchronization process, the stationary reference frame phase-locked loop (SRF-PLL) associated with the voltage source inverter (VSI) is modified using the frequency, voltage deviation, and phase angle information. Furthermore, the islanding process is classified as intentional and unintentional islanding scenarios for achieving efficient transition control. Here, the intentional islanding process is achieved with the information that is available in the system due to the planned disconnection. For the unintentional islanding process, a fuzzy inference system (FIS) is used to modify the conventional droop control using the information of change in active power, voltage, and frequency. To identify the action of the proposed approach during the transition process, numerical simulations are conducted with the hardware-in-loop (HIL) simulator by developing a 10kWp three-phase grid-connected DG system. The results identified the efficient control of the VSI for both islanding and grid connection processes. In the islanding conditions, the proposed controller provides advantage with less detection and disconnection time, and during synchronization, it instantly minimizes the phase-angle deviation to achieve efficient control.

The Influence of Grid-connected Distributed Generation on the Power Supply Reliability of Distribution Network

This paper analyzes the typical distribution network structure and the operating characteristics of distributed generation (DG). By analyzing the impact of grid-connected DG on equipment such as reclosing and spare power automatic switching, we calculate the power supply reliability indexs after the DG is connected to the grid under various operation modes such as reclosing, spare power automatic switching, de-sequencing distributed energy and islanding. Finally, the results of the reliability indexs can provide the theory and data for planning and improving the operating mode of grid-connected DG.

Impact of distributed generation on the Nigerian power network

Distributed generations (DG) are being installed at increasing rates, both in developed and developing countries. The increasing number of DG connected to the distribution system could have a significant impact on the power system operation. This paper presents a case study investigating the impact of grid-connected DG on the Nigerian power network in terms of bus voltages and network losses. The results showed that without DG, some of the bus voltage magnitudes of the test system were outside the permissible voltage limit of 0.95pu≤Vi≤1.05p.u. However, with DG connected, the voltage magnitudes were improved to allowable values. The network active power loss was reduced by 12.03% from 85.60MW to 75.30MW. In this way, the power system becomes more efficient and secured.

Reactive Power Optimization of Distribution Network with Distributed Generators by Improved Evolutionary Programming Algorithm

In the distribution network containing distributed generators (DG), both DG and capacitors can be adjusted for reactive power, and there is a strong complementarity between the two. If the reactive power compensation ability of each grid-connected DG can be fully utilized, it will effectively reduce the voltage fluctuation and the number of equipment actions, which will help to improve the operation level of the distribution network. In this paper reactive power optimization of distribution networks containing distributed power sources has studies. An improved evolutionary programming (EP) method is proposed to solve the optimization goal, using a variable step-size evolution method and optimization strategy with small population and high convergence accuracy. The algorithm improves the random dynamic step method. In different stages of optimization, different step sizes are used to improve the optimization effect. At the same time, considering that some wind farms are equipped with AVC and some wind farms are equipped with capacitor banks, the evolutionary operator is improved. The operator evolves directly on the integer, so it is easier to find the global optimal solution. This paper has used IEEE33 bus system to verification. Results show that the DG can reduce active power loss in distribution network and ameliorate the voltage level. Meanwhile, the improved evolutionary programming method has good optimization effect, fast convergence speed and high search efficiency.

Virtual State Damping for Resonance Suppression and Robustness Improvement in LCL-Type Distributed Generation Inverters

This article proposes a Virtual State Damping (VSD) plugin to output current controllers of distributed generation (DG) inverters. The VSD is designed to suppress the resonance usually present in LCL-type grid-connected DG systems, providing robustness to the control system against grid impedance uncertainties or variations. Typical active damping techniques apply an equivalence impedance model to design their structures. The proposed VSD has the advantage of not needing to take such analysis into account for its design, i.e., it is not dependent on the LCL filter's physical model. The VSD structure applies the model reference theory, and it does not require additional sensors for its implementation. The paper also presents the VSD design methodology and stability analysis. Real-time domain emulation (RTDE) results and 5kW lab-prototype experimental results demonstrate the effectiveness of the proposed technique.

A fault analysis for Micro-grid based on Wavelet

Micro grid is an efficient and flexible way to solve the problem of grid-connected distributed generation. Since the distributed generation accessed and the number of branch increases, system fault condition is complicated. Micro grid fault protection becomes a hot issue now. In this paper, a method based on wavelet is proposed for micro grid fault current analysis. A typical 10kV micro grid model is established in PSCAD, which is consisted of wind power, PV, EV and so on. And, short circuit fault is simulated. Then, the fault current data is further dealt by Harr wavelet. The results would provide a good guide for the setting of fault protection scheme.

Study on a Correlation-Based Anti-Islanding Method under Wider Frequency Trip Settings for Distributed Generation

Islanding phenomenon of distributed generation (DG), such as photovoltaic (PV) generation, is undesirable because it causes safety issues for utility service personnel and power system equipment. Many anti-islanding methods have been studied since DG appeared in electric power systems (EPSs). Most anti-islanding methods focus on disconnecting DG from the grid using functionality to detect islanding under narrow frequency trip settings, because safety issues have a higher priority. However, as DG plays a key part of an EPS, a significant loss of DG due to a short disturbance could result in a reliability issue for the EPS. Corresponding to this matter, new international standards, such as IEEE standard 1547–2018, require more sophisticated and complex functionalities for grid-connected DGs by adopting ride-through technologies and wider voltage/frequency trip settings. Since most anti-islanding functions of inverter-based DG have been based on the frequency of the inverter voltage, it is more difficult to detect islanding under wider frequency trip settings. This paper presents a correlation-based anti-islanding method (AIM) without depending on the frequency trip of inverter-based DGs. Simulation results are provided to verify the performance of the correlation-based anti-islanding method. As a result, the proposed method detects islanding at 0.116 s under wider frequency trip setting by the IEEE Std. 1547–2018 test condition, while the popular active frequency drift method with positive feedback does not detect islanding using the same current disturbance.

Advanced Variable Switching Frequency Control for Improving Weighted Efficiency of Distributed Renewable Generation Systems

Energy conversion efficiency and output current harmonic distortion are two key performance measures of small-scale grid-connected distributed generation (DG) systems. As the interface between renewable energy generators and the utility grid, dc-ac converters (i.e. inverters) have been increasingly used in recent years. In this paper, a novel control algorithm termed “variable switching frequency control (VSFC)” is proposed to increase the weighted efficiency of the inverter for renewable energy generators through selection of optimal switching frequencies of pulse width modulation (PWM) in real time, based on estimation of output current harmonic distortion. Both simulation and experimental results indicate the proposed VSFC algorithm ensures that the inverter can operate with maximum efficiencies at different output levels while satisfying standard requirements for grid current harmonic distortion. Furthermore, implementation of this method to improve the inverter efficiency has no impact on inverter costs or control complexity.

Use of Matrix-Pencil Method for Efficient Islanding Detection in Static DG and a Parallel Comparison With DWT Method

Islanding or nonislanding events in grid-connected distributed generation bring along a typical distinguishable transient signature in its frequency profile. This demarcation leads to the development of a new islanding protection approach, which is based on the estimation of frequency waveform parameter (transient's frequency) by Matrix pencil (MP) method. To demonstrate the efficacy of the proposed MP method, four critical scenarios are considered in this paper for covering all possible disturbance events. These events are also compared along with a discrete wavelet transform (DWT) based islanding detection method in simulations as well as in RT-LAB-based real-time environment. It is noteworthy to mention that the proposed MP method has been found to have a positive edge over the DWT-based method in terms of robustness and chances of misidentification.

Application of resistive super conductor fault current limiter for protection of grid-connected DGs

Penetration of Distributed Generation (DG) into the power system causes technical problems and bad effects on the safety of the system due to increasing the short circuit levels in transmission and distribution networks. So, there will be miscoordination problems of directional over current relays (DOCR) when DGs are integrated with looped power delivery systems. This paper presents a new approach of implementing resistive superconducting fault current limiters (SFCL) with DG units to obtain optimal setting of protection system. The protection coordination setting is optimized using particle swarm optimization (PSO) technique. The proposed algorithm is tested on nine-bus looped power distribution system and the effects of SFCL on protection system of DG-grid connected are analyze. Three cases are studied: no DG, grid-connected DGs with SFCL and grid-connected DGs without SFCL. Several simulations are implemented for different locations of fault.

Dynamic Analysis and Improved LVRT Performance of Multiple DG Units Equipped With Grid-Support Functions Under Unbalanced Faults and Weak Grid Conditions

Due to the increased integration of multiple distributed generation (DG) units into the distribution network, riding through short-term faults and supporting the host grid have been requested by the new grid codes in many countries. However, the literature lacks the detailed dynamic analysis and control coordination of multiple grid-connected converter-based DG units, equipped with advanced controllers in the synchronous reference frame. To fill this gap, this paper initially presents a detailed small-signal modeling framework for typical medium-voltage multi-bus power distribution systems with multiple DG units equipped with grid-support functions to operate under the unbalanced conditions. This model encompasses the positive and negative sequences of the current and voltage and is developed for three stages of the fault (i.e., before, during, and after the fault) to cover a wide range of system operating points. In addition, to precisely study the interactions among DG units, four different control modes in DG units are considered to study the system dynamics under low-voltage and unbalanced conditions and at different grid strengths. Using the proposed detailed state-space models and based on the small-signal stability analyses, different control parameters are redesigned using the eigenvalue analysis on the complete multi-DG system. As a second contribution, sensitivity analyses are performed to study the effects of different system parameters, such as line characteristics, loading levels, and unbalanced fault characteristics, on the stability of the multi-DG system under unbalanced faults. Comparative simulation and experimental results are also reported to show the accuracy and effectiveness of the theoretical analyses.