Different Distributed Generation Research Articles

Power sharing enhancement through a decentralized droop-based control strategy in an islanded microgrid

A decentralized intelligent droop-based control strategy is proposed in this paper for the enhancement of equal active and reactive power sharing in an islanded inverter-based microgrid. Droop control is mostly preferred because it does not need communication facilities for its implementation. However, the presence of different feeder impedances for the different distributed generators (DGs) in a microgrid make reactive power sharing inaccurate. Furthermore, as a result of considerable load changes and different droop characteristics for the DGs, the inverter's output voltage and frequency are altered and these in turn alter the reactive and active power sharing respectively. With these conditions, the generalized droop control (GDC) strategy fails to effectively share load reactive and active power among the DGs. In order to extenuate these challenges, this paper presents a nonlinear autoregressive exogenous neural network droop-based control (NARX-NN DBC) strategy which does not depend on the varying line impedances, droop gains for the different DGs and is less affected by fluctuating loads in the grid. A microgrid, made up of two DGs and a load is modelled in MATLAB/Simulink environment and validation of the proposed control strategy is done through many simulations. Within the simulation runtime, NARX-NN DBC yielded a maximum frequency percentage deviation of 0.46% from the nominal value of 50 Hz whereas GDC yielded 0.62%. Regarding the voltage, NARX-NN DBC gave maximum deviation of 0.026% meanwhile GDC gave 0.079% from the nominal value for 380 V. In addition, during 0.57–0.64 s with load active power demand of 4.6 kW, NARX-NN DBC registered 0.43% power sharing error whereas GDC registered 6.5%. On the other hand, during 0.57–0.64 s, with 5kVAr load power demand, NARX-NN DBC registered 0.2% whereas, GDC registered 2%. These obtained results clearly show that NARX-NN DBC strategy has a better performance compared to GDC strategy with respect to power sharing in an autonomous microgrid.

Precise Fault Location in Active Distribution Systems Using Unsynchronized Source Measurements

This article presents a phase-domain based fault location algorithm for unbalanced power distribution systems with distributed generation. Unsynchronized voltage and current measurements, taken from the sources prior and during the fault, are utilized to calculate the equivalent source impedances and the incremental current quantities required. The latter are substituted into the fault location equations, which are solved to determine the fault resistance(s), the synchronization angles, and the possible fault positions. Multiple possible fault position estimations are eliminated by applying an index-based methodology to find the exact fault position. Extensive simulations are performed for a benchmark distribution system with conventional and inverter-interfaced generation units, considering all types of common short-circuit faults, several fault resistance magnitudes, varying load levels, different distributed generation (DG) mixture, and the impact of line segment length. The results show that fault distance is accurately estimated by the proposed algorithm.

Decentralized TSO-DSO coordination for voltage regulation purposes based on renewable energy sources management – Sensitivity and robustness analyses

• A decentralized coordination between a Transmission System Operator (TSO) and a Distribution System Operator (DSO) implemented via a standardized Business Use Case (BUC) for scheduling and deploying optimal reactive power exchanges in the DSO's boundary for improved voltage control in the TSO's networks is proposed. • The interoperability between the TSO, the DSO, and other stakeholders is solved by designing and developing the BUC within the framework of the International Electrotechnical Commission (IEC) Common Information Model (CIM) family of standards IEC61970, IEC61968, and IEC62325. • The standardized BUC is demonstrated on real-world Slovenian TSO's and DSO's networks. On one hand, a sensitivity analysis is conducted to evaluate to which extent different Renewable Energy Sources (RES), such as capacitor banks and different Distributed Generators (DGs), viz. hydropower, photovoltaic (PV), and thermal (co-generation) units, impact on the high voltage (HV) for different network topologies, DGs’ operating scenarios, and capacitor banks’ sizes and locations. On the other hand, a robustness analysis is conducted to evaluate the capability of the proposed approach to regulate the HV voltage by managing the reactive power injected by these different RES in the different simulated scenarios. • The proposed data exchange mechanism based on the standardized BUC can successfully exchange data between the TSO, the DSO, and other stakeholders, such as the Significant Grid Users (SGUs) and Meter Operators, as a CIM Common Grid Model Exchange Standard (CGMES) format. • The proposed approach can manage DGs at the DSO's boundary toward contributing additional (positive or negative) reactive power to reduce the voltage deviations in the grid, improve the power quality at the DSO's boundary by reducing the flow of reactive power from the TSO's to the DSO's networks and vice versa, and keep the HV within safe values. The increasing penetration of Renewable Energy Sources (RES) in distribution networks has led traditional voltage regulation to their boundaries. In order to develop advanced techniques for voltage control in this new context, an adequate and real-time coordination and communication between Transmission System Operators (TSOs) and Distribution System Operators (DSOs) is needed. In this paper, a decentralized TSO-DSO coordination approach for scheduling and deploying optimal reactive power exchanges in the DSO's boundary for improved voltage control in the TSO's networks is proposed. The proposed approach is implemented via a standardized Business Use Case (BUC). The interoperability between the TSO, the DSO, and other stakeholders is solved by designing and developing the BUC within the framework of the International Electrotechnical Commission (IEC) Common Information Model (CIM) family of standards IEC61970, IEC61968, and IEC62325. In view of the lack of pilot tests in the field, the proposed standardized BUC is demonstrated on real-world Slovenian TSO's and DSO's networks. The simulation experiments presented in this paper are twofold. On one hand, the proposed data exchange mechanism based on the standardized BUC demonstrates the feasibility of successfully exchanging data between the TSO, the DSO, and other stakeholders, such as the Significant Grid Users (SGUs) and Meter Operators, as a CIM Common Grid Model Exchange Standard (CGMES) format. On the other hand, the capability of the proposed decentralized TSO-DSO coordination approach to regulate the High Voltage (HV) by managing the reactive power injected by different RES, such as capacitor banks and different Distributed Generators (DGs), viz. hydropower, Photovoltaic (PV), and thermal (co-generation) units, is validated via sensitivity and robustness analyses for different network topologies, DGs’ operating scenarios, and capacitor banks’ sizes and locations. The simulation results show that the proposed approach can manage DGs toward contributing additional (positive or negative) reactive power to reduce the voltage deviations in the grid, improve the power quality at the DSO's boundary by reducing the flow of reactive power from the TSO's to the DSO's networks and vice versa, and keep the HV voltage within safe values. Unfortunately, this is not the case for the capacitor banks, where the capability of the proposed approach to manage their injected reactive power to regulate the HV voltage is highly dependent on their sizes and location, being necessary to be studied on a case-by-case basis.

An Adaptive Control of Remote Hybrid Microgrid based on the CMPN Algorithm

• The paper proposes a decentralized droop-based control technique power flow through the ILC, meanwhile, to keep the dc microgrid voltage and the ac microgrid frequency within their acceptable ranges. • To overcome the continuous operation of ILC, The modified droop control based CMPN algorithm is used to determine the necessity of operation of hybrid microgrid by estimating the status of the ac and dc microgrids by comparing local measurements with their critical values at both sides. • An adaptive filtering algorithm based on continuous mixed P-norm (CMPN) algorithm is utilized for the proposed autonomous control strategy to insure adaptive tuning of the controller parameters. The variable step size feature of the CMPN algorithm results in fast response compared to other techniques such as robust mixed-norm and the least absolute deviation techniques. The robustness against impulsive noise while having fast convergence, compared to other algorithms, render the CMPN algorithm to be an effective technique for online adaptation of the PI controller used for the ILC, especially in an islanded archetype to maintain the stability of the network. • A comparison between the proposed strategy based on both CMPN algorithm and adaptive PI control under different loading conditions are implemented to validate the proposed methodology. This paper proposes a new adaptive communication-less control strategy to enhance the dynamic performance of the interlinking converter (ILC) of a remote hybrid microgrid. The proposed autonomous strategy is based on the continuous mixed P-norm (CMPN) algorithm to simultaneously maintain the frequency of ac-side and the voltage of dc-side of the ILC within their acceptable ranges under various conditions. The variable step nature of the CMPN algorithm and robustness ensure stable operation of the proposed strategy for the ILC. In addition, the power sharing between both sides of the ILC is achieved by a modified ac-dc droop control to avoid using any communication systems between different distributed generators (DG). Moreover, a simple algorithm is used to determine the desired power flow direction based on local measurements of dc voltage and frequency. The proposed CMPN algorithm provides an online adaption of the controller's parameters to avoid the need for fine tuning or optimization techniques under various operating conditions. The dynamic performance of the proposed autonomous control strategy is evaluated using the PSCAD/EMTDC simulation package under different operating modes. The results demonstrate the superior dynamic performance of the proposed strategy based on the CMPN algorithm compared to the adaptive PI (API) controller in terms of fast response and tight regulation of power flow, voltage and frequency under different conditions. Compared to API, it has been found that the proposed controller results in more improvement of the dc-side voltage within the operating frequency range of the ac-side of the ILC.

Differential Protection Scheme for A Micro Grid with Inverter-Type Sources Based On Positive Sequence Fault Currents

The microgrid (MG) is a coordinated collection of different distributed generation (DG) typesthatsupply local demandthrough a distribution network. MG may operate in two different modes: grid-connected (GC), and islanded (IS)modes.The fault current valuevaries significantly between the GC and IS mode for a MG with inverter-based distributed generators(IBDGs). The fault currents are minimal in the IS mode owing to the power electronics equipment have a limited current carrying capacity. Therefore, the coordination of traditional overcurrent (OC) protection is difficult for these two operation modes. Therefore, a comprehensive MG protection scheme should be established to safeguard MG against all kinds of faults. The main protection strategy proposed in this paperis a positive sequence differential current protection scheme. The envisioned concept can overcome the protective device coordination problems, and all fault types can be detected during both operation modes of MG for radial andloop configurations. The validation of the proposed design is performed using PSCAD/EMTDC software. The results indicate that the maximum fault clearing time for the main protection in GC mode and IS modeisof 31.5 ms and 34 ms respectively. Compared with other schemes, the proposed scheme has a faster clearing time and is less expensive.

Day-Ahead Scheduling of On-Load Tap Changer Transformer and Switched Capacitors by Multi-Pareto Optimality

In this study, a multi-objective optimization method is proposed to solve day-ahead voltage control problems in distribution systems. The main purpose is to determine the optimal schedule for on-load tap changer (OLTC) settings at the sub-station and switched capacitors (SC) based on day-ahead load forecasting. The optimization criteria presented in this study include: (1) minimizing the voltage deviations at the main transformer bus, and (2) minimizing the total power loss. In the proposed method, the Pareto front and Manhattan distance are combined as indices to assess and select the best solution. Multi-Pareto optimality is used to improve the performance of the proposed scheduling strategy. In this study, the network components were modeled by the DIgSILENT Power Factory 15.2, while the multi-objective optimization algorithm was implemented on the MATLAB 2016a software package. Additionally, the effects of different distributed generation (DG) grid-connected points and operation scenarios on voltage control scheduling were examined. The efficiency and performance of the proposed method were verified using an IEEE 33 BUS test system. Compared with the local voltage level (LVL) and reactive power device control (RPDC) methods, the proposed method delivered percentage reductions in (1) voltage deviations at all buses, (2) voltage variations, (3) total system power loss, and (4) difference in values of up to 160.93%, 31.16%, 10.35%, and 434.34%, respectively.

Probabilistic Power Distribution Considering Uncertainty in Load and Distributed Generators Using Cumulant and Truncated Versatile Distribution

Enhanced power flow has a significant effect on the desirable performance of the power system. Implementing of the fair power flow prevents the power system from overload or damage of the elements and provides stable parameters. Considering different distributed generators (DGs) and various loads, balance in the power distribution is a key factor of the stability and reliability of the power system. On the other hand, the uncertainty of DGs and loads causes underestimation of power in the system, which results in a main challenge. In this paper to overcome this challenge, a probabilistic power distribution approach based on using Cumulant and truncated versatile distribution techniques is proposed. Using this approach, the probabilistic models of DGs and load are suggested where the power distribution is desirably performed using adaptive droop control process and employing Cumulant distribution and truncated versatile distribution. Thus, the degradation effect of the uncertainties is compensated where the frequency/voltage deviation from the reference values is minimized. Adaptive droop approach is employed to achieve the stable frequency/voltage, which leads to improved power flow in the total parts of the power system and avoidance in power redistribution cost Simulation results show the efficiency of the proposed method to improve the performance of the system and cost reduction.

Distributed Hierarchical Control for Islanded Microgrids Based on Adjustable Power Consensus

For the problem of power allocation in microgrid hierarchical control, a distributed hierarchical control strategy based on consensus algorithm is proposed. When the load suddenly increases, due to the different adjustable power of different distributed generators (DGs), overcharging and discharging of DGs will result if the increased load is not redistributed. The distributed hierarchical control strategy proposed in this paper defines the proportion between the local increased load and the local adjustable power as the response ratio. With the objective of ensuring that the frequency and voltage of the microgrid can be restored to their rated value, the response ratios of DGs are adjusted by applying the consensus algorithm. Further, the microgrid realizes the reasonable operation of the microgrid by dynamically distributing the increased load in real time. Finally, the feasibility and effectiveness of the proposed strategy is verified by analyzing the stability of the system and building a microgrid simulation model in the Matlab/Simulink simulation platform.

Soft computing fuzzy set through [formula omitted] to identify islanding state of integrated electrical grid at different operational events

Control of integrated utility grid plays important role, as renewable energy sources are rapidly increasing with installation of different Distributed Generation (DG) systems. Issues arising during the operation like interruption, disorder and uncertainty of network to be resolve. One of the situations is island state, and require to secure human beings and converter devices those are working in integrated energy sources environment. Fuzzy sets are to be identifying this state and these are updating with device control parameters of network like voltage, frequency. This paper presents a k-nearest neighbour Machine Learning (knn−ML) to obtain Upper Limit (UL) Lower Limit (LL) of parameters for continuous fuzzy based state estimation. Also proposed knn−ML helps to overcome existing challenges and motivate to better recognition of integrated network state. Outcomes of the paper, to update device control at every Abnormal Mode (AM) of operation and as when system parameter changes at different conditional operating modes. Non Detection Zone (NDZ) is also effectively reduced as per with knn parameter in both [LL, UL] mismatch cases. Mismatch cases of 50% to lower value of 10% is also successful tested with proposed method and a proper trip signal has been generated even at lower mismatch conditions. Effective outcome has been obtained with knn−ML soft computing algorithm.

Optimal Day-Ahead Scheduling for Campus Microgrid by using MILP Approach

In this paper, energy management system (EMS) is proposed for institution which helps in reducing the operational cost with the help of using different distributed generators (DGs) and electric vehicles. For this purpose, a scenario is created in which university is connected with national grid having self-powered PV plant, electric vehicles and a diesel generator. Impact of various distributed generators and optimally scheduled energy storage system (ESS) are analyzed for the university campus which helps in reducing operational cost of energy by using campus load data. The proposed model consist of different distributed generators and their effects are observed in various scenarios. Mix Integer linear programming (MILP) is used to get optimized result and then it is compared with Ant Colony Optimization and Linear programming (LP) techniques. Economic and environmental benefits are also discussed. Operational cost was measured and compared and found the role of ESS by using MILP in minimizing operational cost from $798.560 to $756.3850.

Analysis of Single-phase Grounding Fault with Distributed Generation in Distribution Network

Different distributed generation (DG) types and neutral grounding methods affect single-phase ground fault current characteristics of distribution network. To analyse the single-phase ground fault current characteristics, this paper establishes a single-phase ground fault model with rotating and inverter-type DG accessed using symmetrical component method. By considering different grounding methods of distribution bus side and DG side, distribution characteristics and change laws of fault current as well as sequence currents on both sides of fault point when single-phase short circuits occur in different positions of system are discussed. To verify correctness of analysis, simulation experiments of models is carried out by Simulink. The results of this paper can provide reference for system relay protection configuration and neutral grounding method selection.

Unified Modeling and Hierarchical Control Strategy for Different Distributed Generators in Active Distribution Networks

The growing penetration of renewable energy resources (RESs) increases uncertainties in active distribution networks (ADNs), leading the networks to suffer low inertia, bidirectional power flows, and rapid power changes. The frequency overshoots, overvoltage, and unbalance power sharing are prone to happen in ADNs. To address those issues, this paper proposes a novel unified modeling and a hierarchical control strategy for different distributed generators (DGs). First, to unify the control states of different DGs and separate control states of different control layers, a unified modeling method for grid-following and grid-forming DGs is proposed. Then, based on the unified model, a two-layer control strategy is designed. The robust controllers are locally configured to achieve rapid recovery control, avoiding the impact of communication delays. The collaborative power controller is centralized designed to prevent power circulation caused by the interaction of local controllers of DGs. Compared with other hierarchical control strategies, our strategy can make further use of the residual capacities of different DGs and can more rapidly suppress the unpredictable changes of RESs. The effectiveness of the proposed strategy is validated by several cases in MATLAB/Simulink.

Optimal integration of distributed generation resources in active distribution networks for techno-economic benefits

In recent years, modern electricity utilities face great challenges regarding the deregulated energy markets, transition toward sustainable smart grids and the increased load demand. These challenges are a part of the reasons that have paved the way toward the rapid progress of spreading the different Distributed Generation (DG) technologies into the modern Distribution Networks (DNs). DGs integration into DNs can be employed as a key solution for tackling the problems, facing the distribution systems, and verifying more technical and economic benefits while considering the systems’ uncertainties and the operational policies of the distribution utilities. This paper introduces the application of Modified Sine Cosine Algorithm (MSCA) for enhancing the DNs performance through the integration of multiple DG technologies in order to optimize the active power losses, the fast voltage stability index and the total costs, considering the DGs penetration level as well as the DG units’ operating power factor constraints. The proposed algorithm has been implemented using MATLAB software and applied on three-benchmark IEEE test systems (30-bus, 33-bus and 300-bus) as different models of electric power networks. The attained results show that the suggested optimization platform especially using MSCA, is more effective and successful in determining and finding better results than existing results.

Optimal sizing and positioning of grid integrated distributed generator: a review

The ever-growing population and globalization have resulted into an increase in demand for power. Additionally, ecological concerns like an unnatural weather change have constrained us to locate new and different substitutes to the current conventional sources of energy. To provide a solution to this crisis of energy in a way that is environment friendly, we have focused our attention towards making renewable energy resources as an alternative to currently employed sources of power. This paper contains extensive study on different Distributed Generation (DG) sources, comparing their merits and demerits also comprising of the impact when added to an already existing AC power grid. Accordingly, the planning methodologies have been discussed which will help us in determining which type of DG suits best to our requirement. This paper also contains the review of optimal placement techniques and sizing methodologies for DG system in grid networks, which are together known as Hybrid Energy Systems (HES).Â

A Communication-free Signal Generating Technique for Reactive Power Correction in Islanded Microgrid

The primary function of microgrid (MG) is to share the power accurately among different distributed generation (DG) units according to the load demands. The droop control methods are normally used for appropriate power sharing. However, these control techniques suffer badly due to the feeder impedances and uncontrollable power coupling issues. Many techniques have been proposed to share power accurately, most of them rely on communication link. In this work a localized/communication free signal generating mechanism is proposed. The mechanism injects the transient reactive power in frequency droop characteristics by observing the changes in microgrid. This injection disturbs the actual active power sharing which is helpful for the computation of reactive power sharing errors. These errors are minimized by utilizing the proportional integral (PI) controller. The PI controller modifies the y-intercept and the slop of Q-E (Reactive Power –Voltage) droop characteristic for the correction of reactive power sharing error. Moreover, the parameters of droop and PI controller of inner control loop are optimized by Particle Swarm Optimization (PSO) to obtain high precision and reliability. The proposed technique has the following salient features:1. Accurately shares the reactive power without the information of feeder line impedances2. This accurate reactive power sharing scheme has been started locally without the need of communication signal from the central controller. Thus, there is no delay in monitoring the notable changes in microgrid caused by DGs. 3. The careful selection of PI & droop controller parameters through PSO makes the system more stable as compared to the conventional methods in terms of transients and steady state responses.

High-Bandwidth Secondary Voltage and Frequency Control of VSC-Based AC Microgrid

This paper proposes a novel secondary control strategy for the power-electronic-based ac microgrid. This approach restores the voltage and frequency deviations by utilizing only local variables with very high bandwidth. This is realized with a finite control set model predictive control technique that is adopted in the inner level of the primary control of voltage source converters. In the outer level of the primary control, droop control and virtual impedance loops are exploited to adjust the power sharing among different distributed generation (DGs). As inner control level operates with a very high bandwidth, need for filtering of the calculated active and reactive powers in the outer level of the primary control is insignificant. Therefore, the secondary control can be operated with a far superior bandwidth compared to the case when the conventional cascaded linear control is used. Merits of the proposed approach are investigated analytically with the help of the describing function methodology that allows the quasi-linear approximation of the inner control level. Finally, simulation and experimental results are presented.

Control of Distributed Generators and Direct Harmonic Voltage Controlled Active Power Filters for Accurate Current Sharing and Power Quality Improvement in Islanded Microgrids

Harmonics are regarded as one of the main challenges in a microgrid. This issue may even get worse when different distributed generators (DGs) work together to solve the load sharing problems due to mismatched feeder impedances and diversified DG ratings. Even though load sharing can be achieved, the microgrid suffers from voltage unbalance and total harmonic distortion (THD) issues at the output of DG terminals as well as at the point of common coupling (PCC). Thus, in this paper, the power quality improving method is discussed, with a target of load sharing under the hierarchical control of different DG units and an active power filter (APF) in microgrids. To achieve this objective, we propose integrating a direct harmonic voltage controlled APF with DGs to improve their harmonic compensation performance. This proposed control scheme has many advantages over conventional control using a shunt resistive active power filter (R-APF) with voltage controlled DGs. First, based on the existing THD level of the PCC voltage, the proposed scheme provides improved voltage compensation and reduction in THD in the islanded microgrid. Secondly, equal load sharing can be achieved simultaneously. Thus, the proposed scheme provides better performance and a seamless interface as the proposed study mainly contains both the voltage controlled DGs and the local based voltage detection APF.

Improving Voltage Profile of Islanded Microgrid using PI Controller

<p class="MsoNormal" style="margin-top: 6.0pt; text-align: justify;">In islanding operating mode of microgrid, the voltage and frequency of system must be maintained by the microgrid, or else the system will crumble due to the characteristics of different distributed generators (DG) utilized in microgrid. The voltage and frequency lost provision when main grid is disconnected. This paper presents PI controller based voltage controller to regulate voltage to its normal condition. The controller is proposed to be utilized individually with each distributed generator (DG) in microgrid. The controller compares inverter output voltage with voltage at point of common coupling (PCC) and its output is feed to PWM pulse generator to generate appropriate pulses for inverter to regulate voltage to its nominal value. The simulation results of proposed system are shown using MATLAB/Simulink platform.</p>

A DC Microgrid Coordinated Control Strategy Based on Integrator Current-Sharing

The DC microgrid has become a new trend for microgrid study with the advantages of high reliability, simple control and low losses. With regard to the drawbacks of the traditional droop control strategies, an improved DC droop control strategy based on integrator current-sharing is introduced. In the strategy, the principle of eliminating deviation through an integrator is used, constructing the current-sharing term in order to make the power-sharing between different distributed generation (DG) units uniform and reasonable, which can reduce the circulating current between DG units. Furthermore, at the system coordinated control level, a hierarchical/droop control strategy based on the DC bus voltage is proposed. In the strategy, the operation modes of the AC main network and micro-sources are determined through detecting the DC voltage variation, which can ensure the power balance of the DC microgrid under different operating conditions. Meanwhile, communication is not needed between different DG units, while each DG unit needs to sample the DC bus voltage, which retains the plug-and-play feature of the DC microgrid. The proposed control strategy is validated by simulation on a DC microgrid with permanent magnet synchronous generator-based wind turbines, solar arrays and energy storage batteries, which can be applied to small commercial or residential buildings.

An Overview on Operation and Control of Microgrid

A microgrid is a complex network with different distributed generators (DG) and loads operating to provide electrical energy for local loads. It can operate in grid-connected or islanded mode, which has the ability to enhance the reliability and stability of electrical energy supply. Most of micro sources in a microgrid are interfaced through power electronic converters. It is an important task for different types of micro sources to be connected and form a microgrid. A lot of control strategies are used in microgrid to achieve stable and reliable operation and smooth switching between two operation modes.