Distributed Generation Sources Research Articles

Dynamic dispatch optimization of microgrid based on a QS-PSO algorithm

A microgrid (MG) has been regarded as an efficient way for integrating distributed generation sources (DGSs) into distribution systems, and the corresponding effective energy management is crucial to realize the benefits associated with MG. In general, most of the researches ignored the inherent coupling among the dispatch intervals. This study aims to establish a dynamic dispatch optimization model for reasonably scheduling the DGSs in the MG and to identify the optimal solution based on a swarm intelligence algorithm. With the introduction of the dynamic system theory, a dynamic multi-objective optimization model is established for minimizing the operation and maintenance cost of the MG, decreasing the pollutant emissions, and reducing the deprivation cost of the DGSs. In order to deal with this complex optimization problem with high-dimension variables and multiple constraints, an enhanced quorum sensing based particle swarm optimization (QS-PSO) algorithm, whose competitiveness has been verified, is successively applied for determining the optimal dispatch solution of the whole period, instead of dividing the entire dispatch period into a number of small time intervals via a static optimization approach. The results based on a series of numerical simulations validate the effectiveness of the proposed dispatching model and QS-PSO application and demonstrate the superiority of dynamic operation optimization over the static optimization.

Effects of Distributed Generation on Overcurrent Relay Coordination and an Adaptive Protection Scheme

Integration of distributed generation (DG) such as renewable energy sources to electrical network becomes more prevalent in recent years. Grid connection of DG has effects on load flow directions, voltage profile, short circuit power and especially protection selectivity. Applying traditional overcurrent protection scheme is inconvenient when system reliability and sustainability are considered. If a fault happens in DG connected network, short circuit contribution of DG, creates additional branch element feeding the fault current; compels to consider directional overcurrent (OC) protection scheme. Protection coordination might get lost for changing working conditions when DG sources are connected. Directional overcurrent relay parameters are determined for downstream and upstream relays when different combinations of DG connected singular or plural, on radial test system. With the help of proposed flow chart, relay parameters are updated and coordination between relays kept sustained for different working conditions in DigSILENT PowerFactory program.

Synchronisation of two separate zones in a standalone microgrid

Standalone microgrids that comprise distributed generation sources (DGSs) or energy storage systems (ESSs) exist on off-shore islands or remote areas. When a fault occurs in a standalone microgrid, the microgrid is separated into several zones with pre-specified DGS or ESS supplying power to local loads. After the fault is cleared, the three-phase voltages and frequencies may differ among these zones. To restore the original microgrid topology, these zones must be reconnected to each other by synchronisation. A synchronisation controller of the DGS/ESS that accounts for slightly different three-phase voltages and frequencies in two separate zones is presented. The Clark transform and Mamdani fuzzy rules are used to implement the controller, providing fast and seamless synchronisation. Simulation results using a standalone microgrid show the practical applicability of the proposed method.

CALCULATION OF LOSSES OF ACTIVE POWER AND ENERGY IN TRANSMISSION LINES AND TRANSFORMERS, AS A PART OF THE ELECTRICAL DISTRIBUTION POWER NETWORK

The paper inhere discusses the impact of renewable distributed generation sources upon the power and energy losses in electrical distribution power networks where these sources are attached. In addition a set of mathematical expressions to calculate these active power and energy losses are presented with the respective examples and implementation.

Effective power transfer scheme for a grid connected hybrid wind/photovoltaic system

A new topology and effective power transfer scheme with minimum number of converters is proposed for a grid connected wind/photovoltaic (PV) system. Distributed generation sources considered are permanent magnet synchronous generator (PMSG)-based wind energy conversion system and PV array system. Two voltage source converters with a common DC-link serve as wind side converter (WSC) and grid side converter (GSC), respectively. The PV array is directly tied to the DC link without any power converter providing variable DC-link voltage. The Perturb and Observe technique extracts the maximum power from PV and the DC-link voltage is set to the maximum power point (MPP) voltage of the PV array. The output DC voltage of WSC is regulated to an MPP PV voltage using an outer proportional–integral voltage control loop. The maximum power from the PMSG and stator voltages is utilised to generate the reference currents for WSC to make stator currents to follow stator voltages. With unity power factor control, the overall VA of the WSC would contribute to the active power transfer and thereby reduce the kVA rating of the WSC in the proposed configuration. GSC tracks the maximum power from wind and PV array, and serves as a shunt active power filter to compensate for the current unbalance due to the connection of non-linear loads at the grid. All these functions are accomplished simultaneously. Various power transfer modes of operation are simulated through MATLAB/Simulink software and its results are validated through dSPACE Digital Signal Processor.

Optimal placement and sizing of wind / solar based DG sources in distribution system

Proper placement and sizing of Distributed Generation (DG) in distribution system can obtain maximum potential benefits. This paper proposes quantum particle swarm algorithm (QPSO) based wind turbine generation unit (WTGU) and photovoltaic (PV) array placement and sizing approach for real power loss reduction and voltage stability improvement of distribution system. Performance modeling of wind and solar generation system are described and classified into PQ\\PQ (V)\\PI type models in power flow. Considering the WTGU and PV based DGs in distribution system is geographical restrictive, the optimal area and DG capacity limits of each bus in the setting area need to be set before optimization, the area optimization method is proposed . The method has been tested on IEEE 33-bus radial distribution systems to demonstrate the performance and effectiveness of the proposed method.

TAKING INTO ACCOUNT OF THE INFORMATION UNCERTAINTY IN THE MULTICRITERIA EVALUATION OF ALTERNATIVES OF DISTRIBUTED GENERATION INTEGRATION

In solving problems of planning modes of operation in the existing distribution systems one will inevitably face the necessity of accounting information uncertainty. Moreover, the significance of this factor is enhanced in the case of appearance of distributed generation sources, particularly if they are focused on the use of renewable energy, in the structure of electrical networks. It is obvious that the effectiveness and the impact on the electric networks modes of operation indicators (such as energy losses, voltage profile, reliability) implemented sources of generation are largely dependent on their settings and locations. At the same time, taking into account the different physical nature and dimension of aforementioned characteristics, they can not be represented by a single integral indicator. Taking this circumstance into account a modification of one of the methods of multi-criteria comparison of alternatives is developed in this article to select the optimal variant of the use of distributed generation performed for conditions when a number of modes of operation characteristics are given as a fuzzy quantitative and qualitative variables in the form of fuzzy sets.

A Review of Distributed Control Techniques for Power Quality Improvement in Micro-grids

Micro-grid is typically visualized as a small scale local power supply network dependent on distributed energy resources (DERs) that can operate simultaneously with grid as well as in standalone manner. The distributed generator of a micro-grid system is usually a converter-inverter type topology acting as a non-linear load, and injecting harmonics into the distribution feeder. Hence, the negative effects on power quality by the usage of distributed generation sources and components are clearly witnessed. In this paper, a review of distributed control approaches for power quality improvement is presented which encompasses harmonic compensation, loss mitigation and optimum power sharing in multi-source-load distributed power network. The decentralized subsystems for harmonic compensation and active-reactive power sharing accuracy have been analysed in detail. Results have been validated to be consistent with IEEE standards.

Research on Stochastic Optimal Operation Strategy of Active Distribution Network Considering Intermittent Energy

Active distribution networks characterized by high flexibility and controllability are an important development mode of future smart grids to be interconnected with large scale distributed generation sources including intermittent energies. However, the uncertainty of intermittent energy and the diversity of controllable devices make the optimal operation of distribution network a challenging issue. In this paper, we propose a stochastic optimal operation strategy for distribution networks with the objective function considering the operation state of the distribution network. Both distributed generations and flexible loads are taken into consideration in our strategy. The uncertainty of the intermittent energy is considered in this paper to obtain an optimized operation and an efficient utilization of intermittent energy under the worst scenario. Then, Benders decomposition is used in this paper to solve the two-stage max-min problem for stochastic optimal operation. Finally, we test the effectiveness of our strategy under different scenarios of the demonstration project of active distribution network located in Guizhou, China.

Optimal Siting of Distributed Generators in a Distribution Network using Artificial Immune System

<p>Distributed generation (DG) sources are being installed in distribution networks worldwide due to their numerous advantages over the conventional sources which include operational and economical benefits. Random placement of DG sources in a distribution network will result in adverse effects such as increased power loss, loss of voltage stability and reliability, increase in operational costs, power quality issues etc. This paper presents a methodology to obtain the optimal location for the placement of multiple DG sources in a distribution network from a technical perspective. Optimal location is obtained by evaluating a global multi-objective technical index (MOTI) using a weighted sum method. Clonal selection based artificial immune system (AIS) is used along with optimal power flow (OPF) technique to obtain the solution. The proposed method is executed on a standard IEEE-33 bus radial distribution system. The results justify the choice of AIS and the use of MOTI in optimal siting of DG sources which improves the distribution system efficiency to a great extent in terms of reduced real and reactive power losses, improved voltage profile and voltage stability. Solutions obtained using AIS are compared with Genetic algorithm (GA) and Particle Swarm optimization (PSO) solutions for the same objective function.</p>

A new coordinated backup protection scheme for distribution network containing distributed generation

This paper proposes a new backup protection scheme, named coordinated backup protection (CBP) scheme, for distribution networks containing distributed generation. The proposed protection scheme takes into account the issues faced by traditional backup protection, such as difficulty in setting parameters and complex cooperation, and considers the features of distribution networks, such as changeable power flow because of high penetration of distributed generation sources and insufficient measuring quantities. The CBP scheme includes two aspects: coordinated substation protection and regional master substation protection, who also work as nearby backup protection and remote backup protection respectively. The two protections support each other by local information coordination and regional information sharing, in order to improve the reliability of fault identification. The configuration principles and performances of the proposed backup protection scheme are addressed in the paper. Different fault conditions in the IEEE 14-node system have been used to illustrate and verify the feasibility of the CBP scheme.

Use of superconducting fault current limiters for mitigation of distributed generation influences in radial distribution network fuse–recloser protection systems

In this study, extensive dynamic simulation studies are carried out to explore the impact of synchronous machine (SM)-based distributed generation (DG) integration on existing radial fuse–recloser protection infrastructure. Furthermore, dynamic simulation studies are also conducted to highlight the use of superconducting fault current limiters (SFCLs) to mitigate such an impact. These studies have included the effects of SM-based DG sources on fuse–recloser coordination and recloser sensitivity adequacy. In addition, a comparison between the performances of two different SFCL types has been also offered. The dynamic results of these investigations have shown that the presence of SFCLs has prevented any excessive fault current contribution from SM-based DG sources, as a result, it has restored the fuse–recloser coordination and recloser sensitivity adequacy. Within the frame of reference of the study is the dynamic simulations of a test benchmark that have been conducted using the PSCAD/EMTDC software.

Optimal energy management of the smart parking lot under demand response program in the presence of the electrolyser and fuel cell as hydrogen storage system

Nowadays, utilization of distributed generation sources and electric vehicles (EVs) are increased to reduce air pollution and greenhouse gas emissions. Also, intelligent parking lots (IPL) are increased in response to the increase in the number of EVs. Therefore, optimal operation of distributed generation sources and IPL in the power market without technical scheduling will follow some economic problems for the owner of IPL and some technical problems for the operator of distribution network. Therefore, in this paper, an optimal energy management has been proposed for an IPL which includes renewable energy sources (wind turbine and photovoltaic system) and local dispatchable generators (micro-turbines). Also, determination of optimal charge and discharge powers of hydrogen storage system (HSS) containing electrolyser, hydrogen storage tanks and fuel cell has been considered in the proposed model. Furthermore, the time-of-use rates of demand response program are proposed to flatten the load curve to reduce the operation cost of IPL. The objective function includes minimizing the operation costs of upstream grid and local dispatchable generators as well as charging and discharging cost of IPL subject to the technical and physical constraints under demand response program in the presence of HSS. The proposed model is formulated as a mixed-integer linear programming and solved using GAMS optimization software under CPLEX solver. Four case studies are investigated to validate the proposed model to show the positive effects of demand response program and HSS on reduction of IPL’s operation cost.

Hybrid Technique for Locating and Sizing of Renewable Energy Resources in Power System

In the paper, a hybrid technique is proposed for detecting the location and capacity of distributed generation (DG) sources like wind and photovoltaic (PV) in power system. The novelty of the proposed method is the combined performance of both the Biography Based Optimization (BBO) and Particle Swarm Optimization (PSO) techniques. The mentioned techniques are the optimization techniques, which are used for optimizing the optimum location and capacity of the DG sources for radial distribution network. Initially, the Artificial Neural Network (ANN) is applied to obtain the available capacity of DG sources like wind and PV for 24 hours. The BBO algorithm requires radial distribution network voltage, real and power loss for determining the optimum location and capacity of the DG. Here, the BBO input parameters are classified into sub parameters and allowed as the PSO algorithm optimization process. The PSO synthesis the problem and develops the sub solution with the help of sub parameters. The BBO migration and mutation process is applied for the sub solution of PSO for identifying the optimum location and capacity of DG. For the analysis of the proposed method, the test case is considered. The IEEE standard bench mark 33 bus system is utilized for analyzing the effectiveness of the proposed method. Then the proposed technique is implemented in the MATLAB/simulink platform and the effectiveness is analyzed by comparing it with the BBO and PSO techniques. The comparison results demonstrate the superiority of the proposed approach and confirm its potential to solve the problem

Analysis and modelling regarding frequency regulation of power systems and power supply–demand‐control based on penetration of renewable energy sources

As a large amount of distributed generations power supply is introduced, there is concern about the problem of threatening stable power supply such as voltage rise, fluctuation of the distribution line locally, frequency fluctuation and power regulation shortage in a wide area. In additional, regarding the measures against the supply-demand imbalance and frequency problems, it is necessary to consider not only introducing further distributed generation sources but also new approaches such as utilization of storage batteries or load side control seen in demand response. Against this backdrop, in Japan, an analytical model for supply-demand control/frequency regulation simulation has been developed, which, named AGC30, can work on MATLAB/Simulink. It is possible to simulate the supply and demand balance control considering both economic dispatching control and load frequency control. In this research, with the purpose of contribution to the development of supply-demand control technology that responds to the future large structural change of electric power system, as the introduction and diffusion of renewable energy power generation and smart grid technology, as a common foundation for the supply-demand / frequency control of electric power system, it is aimed to construct a standard model for computer simulation that can be implemented efficiently.

Optimization of virtual power plant with a distributed generation

The article is devoted to the task of optimizing the structure of virtual power plants (VPP) with distributed generation sources. The solution of the problem is based on the structural topological and probabilistic-statistical analysis of the VPP structure. An algorithm for estimating the structure of VPP has been developed. The optimization criteria for VPP are proposed and investigated. The criteria allow to evaluate VPP structural properties and to take into account the inconstancy of generation from renewable energy sources (RES) in VPP composition.

A Comprehensive Review of Protection Schemes for Distributed Generation

Due to the increasing demand of energy and the need for nonconventional energy sources, distributed generation (DG) has come into play. The trend of unidirectional power flow has been gradually shifting. With new technology comes new challenges, the introduction of DG into the conventional power system brings various challenges; one of the major challenges is system protection under DG sources. These sources pose a significant challenge due to bidirectional flows from DGs as well as lower fault current contribution from inverter interfaced DGs. This paper reviews existing protection schemes that have been suggested for active distribution networks. Most of these protection strategies apply only to smaller distribution systems implying that they may need to be extended to larger systems with a much higher penetration of distributed generation. In the end, a potential protection scheme has also been recommended as a future work.

A Dual-Buck–Boost AC/DC Converter for DC Nanogrid With Three Terminal Outputs

Due to the widely used dc characterized loads and more distributed power generation sources, the dc nanogrid becomes more and more popular, and it is seen as an alternative to the ac grid. For safety considerations, the dc nanogrid should provide reliable grounding for the residential loads such as the low-voltage ac power system. There are three typical grounding configurations for a dc nanogrid: the united grounding, the unidirectional grounding, and the virtual isolated grounding. Each grounding configuration has its own specifications to ac/dc converters. In this paper, a dual-buck–boost ac/dc converter for use in the united-grounding-configuration-based dc nanogrid with three terminal outputs is proposed. The working principle of this converter is presented in detail through analyzing the equivalent circuits. Experiments are carried out to verify the theoretical analysis.

Impact of Distributed Generation on the Reliability of Local Distribution System

With the growth of distributed generation (DG) and renewable energy resources the power sector is becoming more sophisticated, distributed generation technologies with its diverse impacts on power system is becoming attractive area for researchers. Reliability is one of the vital area in electric power system which defines continuous supply of power and customer satisfaction. Around the world many power generation and distribution companies conduct reliability tests to ensure continues supply of power to its customers. Uttermost reliability problems in power system are due to distribution network. In this research reliability analysis of distribution system is done. The interruption frequency and interruption duration increases as the distance of load points increase from feeder. Injection of single DG unit into distribution system increase reliability of distribution system, injecting multiple DG at different locations and near to load points in distribution network further increases reliability of distribution system, while introducing multiple DG at single location improves reliability of distribution system. The reliability of distribution system remains unchanged while varying the size of DG unit. Different reliability tests were done to find the optimum location to plant DG in distribution system. For these analyses distribution feeder bus 2 of RBTS is selected as case study. The distribution feeder is modeled in ETAP, ETAP is software tool used for electrical power system modeling, analysis, design, optimization, operation, control, and automation. These results can be helpful for power utilities and power producer companies to conduct reliability tests and to properly utilize the distributed generation sources for future expansion of power systems.

Optimal air-conditioning load control in distribution network with intermittent renewables

The coordinated operation of controllable loads, such as air-conditioning load, and distributed generation sources in a smart grid environment has drawn significant attention in recent years. To improve the wind power utilization level in the distribution network and minimize the total system operation costs, this paper proposes a MILP (mixed integer linear programming) based approach to schedule the interruptible air-conditioning loads. In order to mitigate the uncertainties of the stochastic variables including wind power generation, ambient temperature change, and electricity retail price, the rolling horizon optimization (RHO) strategy is employed to continuously update the real-time information and proceed the control window. Moreover, to ensure the thermal comfort of customers, a novel two-parameter thermal model is introduced to calculate the indoor temperature variation more precisely. Simulations on a five node radial distribution network validate the efficiency of the proposed method.