Islanded Distribution Network Research Articles

Optimal adaptive decentralized under-frequency load shedding for islanded smart distribution network considering wind power uncertainty

The increasing share of renewable distributed generations has raised a challenge about the frequency stability. Under-frequency load shedding (UFLS) can deal with this challenge, but it usually considers a prorated load-shedding strategy and neglects the impact of uncertainty from renewable generation. This may result in unnecessary additional economic losses from the system blackout. In this paper, a risk-decision-based optimal adaptive decentralized UFLS method is proposed to coordinate the distribution of shedding load in the smart distribution network to avoid unnecessary additional economic losses, while considering the wind power uncertainty. Firstly, the uncertainty from wind power generation is modeled by confidence intervals and evaluated by the calculation of the conditional value at risk (CVaR). Then, to economically distribute the power deficit among load agents, a decentralized consensus on the incremental cost among decentralized agents is reached, where the interruption cost of the local agent varies with its load as a nonlinear relationship. Finally, a two-layer adaptive risk-decision decentralized UFLS control framework is proposed to enable the frequency stability and economic operation of the smart distribution network. With the proposed strategy, local information sharing and important global information discovery are achieved in a distributed way. Simulations on an improved IEEE 33-bus system show that the proposed strategy can effectively avoid rigid shedding and implement the optimal allocation of the system power deficit.

Optimal configuration of distributed energy storage considering intending island recovery in faulty distribution networks

With the rapid development of distributed generation, represented by photovoltaic power, the access of a large number of distributed generation poses threats to the security and reliable operation of islanded distribution networks. However, relying on the distributed energy storage system can stabilize the island power supply, which can effectively improve the reliability of the island distribution network. To this end, under the premise of knowing photovoltaic output and load forecast curve, this paper proposes a distributed energy storage optimization configuration method in the active islanding operation mode of multi-source distribution network, which satisfies the “N-1″ safety criterion. First, this paper establishes an optimization configuration model for distributed energy storage with multiple objectives, including minimizing the load shedding in the non-fault loss of power zone, the initial investment cost of distributed energy storage, the node voltage deviation and the system frequency offset. Then, aiming at the islanded power flow calculation process mentioned above, an improved trust region algorithm is proposed, and integrating this method with the harmony search algorithm and ”N-1″ safety criterion solves the model. Finally, the IEEE 33-node distribution system is used to test the performance of the proposed algorithm. The results show that the proposed improved trust region algorithm has the advantages of fast convergence speed and short time-consumption compared with the traditional trust region algorithm. And the proposed optimization configuration scheme for distributed energy storage can satisfy the “N-1″ safety criterion of the distribution network under different fault scenarios.

Analytic hierarchy process-based optimal load scheduling framework in an islanded distribution network

This paper proposes an analytic hierarchy process (AHP) based optimal load scheduling (AOLS) framework in an islanded distribution network to schedule power among prioritized loads under limited generation conditions. The scheduling problem is solved in two stages: in the first stage, AHP is used to determine the priority ranking of loads by assigning weights that are calculated based on the relative importance of loads and their attributes; in the second stage, optimal load scheduling is implemented by minimizing the total cost of load curtailment, subjected to network constraints and security limits. The scheduling problem is solved in four different cases by varying the total power generation using General Algebraic Modeling System (GAMS) to supply power to the loads in the order of priority. Taking the modified IEEE 34 node distribution network as an example, a simulation study is performed to show that the total cost of load curtailment according to AOLS is 18.51%, 24.86%, 28.65%, and 31.54% less than that of optimal load scheduling framework with equal weightage to all loads (OLSEW) in cases 1, 2, 3 & 4, which verifies the effectiveness of the proposed AOLS framework.

Effective Utilization of Distributed Power Sources under Power Mismatch Conditions in Islanded Distribution Networks

The integration of distributed generation (DG) into a power distribution network allows the establishment of a microgrid (MG) system when the main grid experiences a malfunction or is undergoing maintenance. In this case, the power-generating capacity of distributed generators may be less than the load demand. This study presents a strategy for the effective utilization of deployed active and reactive power sources under power mismatch conditions in the islanded distribution networks. Initially, the DGs’ and capacitors’ optimal placement and capacity were identified using the Jaya algorithm (JA) with the aim to reduce power losses in the grid-connected mode. Later, the DG and capacitor combination’s optimal power factor was determined to withstand the islanded distribution network’s highest possible power demand in the event of a power mismatch. To assess the optimal value of the DG–capacitor pair’s operating power factor (pfsource) for the islanded operation, an analytical approach has been proposed that determines the best trade-off between power losses and the under-utilization of accessible generation. The test results on 33-bus and 69-bus IEEE distribution networks demonstrate that holding the islanded network’s load power factor (pfload) equal to pfsource during the power imbalance conditions allows the installed distributed sources to effectively operate at full capacity. As expected, the proposed strategy will assist the utility companies in designing efficient energy management or load shedding schemes to effectively cope with the power mismatch conditions.

Multi-period optimal scheduling framework in an islanded smart distribution network considering load priorities

Multi-period optimal scheduling framework in an islanded smart distribution network considering load priorities

A successive MISOCP algorithm for islanded distribution networks with soft open points

A successive MISOCP algorithm for islanded distribution networks with soft open points

Coyote optimization algorithm for optimal allocation of interline –Photovoltaic battery storage system in islanded electrical distribution network considering EV load penetration

In current times, there is a need to do power system planning to endure situations of any kind. An islanding operation is one such unavoidable situation that may be required in many cases for both technical and economic reasons. First and foremost, this paper focuses on the determination of the best allotment of Interline-Photovoltaic (I-PV) system as per Electric Vehicle (EV) load penetration in the network. With different operational constraints, a multi-objective optimization using real power loss and voltage deviation index is formulated and solved using the Coyote Optimization Algorithm (COA).The paper highlights the computational efficiency of COA with Particle Swarm Optimization (PSO) and Grey Wolf Optimizer (GWO), in addition to various literary works, and the results suggest the superiority of COA by its global optima. The required battery energy storage system (BESS) capacity for supplying an islanded network's entire load demand for a day is determined in the second stage. The simulations were carried out on the IEEE 33-bus electrical distribution network (EDN) contemplating different levels of EV load penetration. The proposed methodology results have proved that the required energy is provided by optimal I-PV-BESS backup for a daylong islanding operation and its adaptability for practical situations.

Adaptive Under-Frequency Load Shedding Scheme for Islanded Distribution Network based on Swing Equation

Adaptive Under-Frequency Load Shedding Scheme for Islanded Distribution Network based on Swing Equation

Impact of photovoltaic systems on voltage stability in islanded distribution networks

This work analyses the impact of photovoltaic generation on voltage stability margin in an islanded microgrid. An indicator of voltage collapse proximity, based on the maximum deliverable power, is used to study the contribution of photovoltaic generation to the voltage stability margin. In this context, the well-known power–voltage curves, also known as ‘nose’ curves, are developed, taking into account different levels of photovoltaic penetration. Furthermore, the effect of the power factor at the photovoltaic generators as well as the influence of the adopted model for such generators are also investigated. The results have shown that the photovoltaic generation can significantly affect the voltage stability margin.

Three‐phase voltage control method by single‐phase distributed generators connected to islanded distribution network

AbstractWe have proposed a concept model of emergency islanded operation by using distributed generators (DGs) such as photovoltaics, electric vehicles, or batteries, which can provide power to customers via undamaged distribution network in order to develop the resilient power system against large disasters, and it is named Islanded Distribution Network (IDN). Since there is no guarantee that the three‐phase generation system is interconnected to the IDN, the single‐phase DGs that are installed in the distribution network may be treated as main generators in the IDN operation. If the IDN has only single‐phase DGs, it is difficult to regulate the three‐phase voltage within the allowable range and to compensate the unbalance voltage. The aim of this study is to develop the method to supply three‐phase balanced voltage by single‐phase generators in the IDN. First, the operating condition of the generators is proposed for the supply of three‐phase balanced voltage in the IDN model by algebra calculation. The control method for three single‐phase generators has been developed by using the conditions obtained from the derivation of the generators conditions.

Three-phase Voltage Control Method by Single-phase Distributed Generators Connected to Islanded Distribution Network

Three-phase Voltage Control Method by Single-phase Distributed Generators Connected to Islanded Distribution Network

Application of Hybrid Meta-Heuristic Techniques for Optimal Load Shedding Planning and Operation in an Islanded Distribution Network Integrated with Distributed Generation

In a radial distribution network integrated with distributed generation (DG), frequency and voltage instability could occur due to grid disconnection, which would result in an islanded network. This paper proposes an optimal load shedding scheme to balance the electricity demand and the generated power of DGs. The integration of the Firefly Algorithm and Particle Swarm Optimization (FAPSO) is proposed for the application of the planned load shedding and under frequency load shedding (UFLS) scheme. In planning mode, the hybrid optimization maximizes the amount of load remaining and improves the voltage profile of load buses within allowable limits. Moreover, the hybrid optimization can be used in UFLS scheme to identify the optimal combination of loads that need to be shed from a network in operation mode. In order to assess the capabilities of the hybrid optimization, the IEEE 33-bus radial distribution system and part of the Malaysian distribution network with different types of DGs were used. The response of the proposed optimization method in planning and operation were compared with other optimization techniques. The simulation results confirmed the effectiveness of the proposed hybrid optimization in planning mode and demonstrated that the proposed UFLS scheme is quick enough to restore the system frequency without overshooting in less execution time.

Application of Meta-Heuristic Techniques for Optimal Load Shedding in Islanded Distribution Network with High Penetration of Solar PV Generation

Recently, several environmental problems are beginning to affect all aspects of life. For this reason, many governments and international agencies have expressed great interest in using more renewable energy sources (RESs). However, integrating more RESs with distribution networks resulted in several critical problems vis-à-vis the frequency stability, which might lead to a complete blackout if not properly treated. Therefore, this paper proposed a new Under Frequency Load Shedding (UFLS) scheme for islanding distribution network. This scheme uses three meta-heuristics techniques, binary evolutionary programming (BEP), Binary genetic algorithm (BGA), and Binary particle swarm optimization (BPSO), to determine the optimal combination of loads that needs to be shed from the islanded distribution network. Compared with existing UFLS schemes using fixed priority loads, the proposed scheme has the ability to restore the network frequency without any overshooting. Furthermore, in terms of execution time, the simulation results show that the BEP technique is fast enough to shed the optimal combination of loads compared with BGA and BPSO techniques.

Improving the energy efficiency of an islanded distribution network using classical and innovative computation methods

The paper presents the analysis of some potentially suitable actions for reducing the energy losses of an islanded Medium Voltage distribution network, with the aim of improving electricity distribution efficiency. For this purpose, four actions are considered: 1) increasing the network's rated voltage; 2) reactive power compensation through static capacitor banks; 3) reactive power compensation through switchable capacitor banks; 4) installation of distributed photovoltaic (PV) generation. The first two measures are typically taken into account by the distribution system operators and can be examined by means of classical design methods, whereas the latter two more innovative actions are tested here using specialized software based on the NSGA-II multi-objective optimization algorithm. The fourth action, expanding distributed PV generation, can be motivated through public or private incentives. It is investigated here using an innovative approach to the optimization problem formulation considering the perspectives of both the utility and the consumer. A case study on a small Mediterranean island real existing network is also presented.

Adaptive Decentralized Under-Frequency Load Shedding for Islanded Smart Distribution Networks

Frequency stability of islanded smart distribution networks with peer-to-peer (P2P) controlled distributed generators (DGs) has attracted special attention recently. Using power line communication (PLC) technology, a multi-agent system (MAS)-based, decentralized, under-frequency load shedding (UFLS) scheme is investigated in this study for smart distribution networks with the communication constraint that each agent can only communicate with its neighboring agents. The proposed scheme uses the two-layer nearest neighbor consensus algorithm (NNCA) to overcome the drawback of the leader–follower consensus algorithm and guarantee the implementation of a decentralized UFLS. Based on the global information (i.e., the magnitude of the total active power imbalance) discovered in the first layer of the NNCA, the multi-stage UFLS can be executed by the second layer of the NNCA. Simulation results demonstrate that the proposed scheme can effectively implement the decentralized UFLS while maintaining the frequency stability of an islanded smart distribution network.

Modified centralized ROCOF based load shedding scheme in an islanded distribution network

This paper presents two centralized adaptive under frequency load shedding (UFLS) methods based on loads willing to pay (WTP) and new objective function. The objective function is considered to minimize load shedding penalties that are paid by distribution network operator (DNO), using optimal algorithm. Maintaining DG units in an islanded distribution system is proposed to prevent system blackout. One of the most important protection schemes to prevent a system blackout is UFLS method. In our proposed UFLS method, amount of load shedding is dependent on loads priority table and intensity of event. Loads priority table is formed, using rate of change of frequency of loads (ROCOFL) indices. Proposed techniques apply the amount of loads active power every few minutes to update loads priority table. These proposed UFLS methods are implemented on the 14-bus Danish distribution system in 3 different load scenarios and are compared with a conventional approach.

Under-Frequency Load Shedding scheme for islanded distribution network connected with mini hydro

Under-Frequency Load Shedding (UFLS) is a common technique to maintain power system stability by removing the overload in some part of the system. The existing UFLS schemes operate successfully in the interconnected grid system. A particular approach of UFLS scheme is required for an islanded system which is known to be not as strong as the grid. This paper presents a new approach of UFLS scheme for the implementation in an islanded distribution system. The scheme is based on a combination of adaptive and intelligent techniques. The disturbance magnitude for response based and event based is treated differently: (1) event based is based on the power imbalance and (2) response based is based on the swing equation which relies on the frequency and rate of change of frequency measurement. Dynamic simulation on an intentional islanding operation is performed on an existing Malaysian network interconnected with a mini hydro generation. The objective is to investigate the effectiveness of the proposed scheme. The simulation results demonstrate that the proposed scheme is capable of improving the frequency response of the islanded system. A significant finding is that the scheme can successfully reduce the effect of power deficiency following the grid connected to islanding operation transition.