Distributed Generation Sources Research Articles

A Benchmark Distribution System for Investigation of Residential Microgrids With Multiple Local Generation and Storage Devices

A benchmark distribution system is developed for investigating control and energy management of distributed generation (DG) at a residential level in the form of three single-phase microgrids. The benchmark is derived from a typical distribution network architecture with common parameters found in North-America systems including wiring specifications, line impedances and connection details for rooftop PV systems. This benchmark system can accommodate microgrids operating in both grid-connected and islanded modes. Within this benchmark, multiple single-phase DG sources located in different phases can be coordinated to form a dynamically balanced three phase system under different load and generation profiles in different phases. The coordination of DG sources in a particular phase is achieved through an intra-phase power management device, while mitigating loads and generation imbalance among all phases are done by an inter-phase power management scheme. It is expected that this benchmark system will facilitate investigation of impacts posed by proliferation of single-phase distributed generation devices and local storage systems in private residences. Three case studies have been carried out to demonstrate the versatility and effectiveness of this benchmark system.

A methodological Decision-Making support for the planning, design and operation of smart grid projects

Planning and operation of Smart energetic have become more complex to analyse due to structural changes in the energy sector. The inclusion of distributed generation sources, generation with renewable sources, storage systems, and the dislocation of information between the different organization levels and actors lead to the inherent difficulty of defining appropriate models that help decision making. Nowadays, decisions in planning and operation are made level by level rather than integrated manner. To address this problem, this work proposes a multi-level methodological framework based on Key Performance Indicators and System of Systems concepts. Involving methods, both quantitative and qualitative, this work serves as guidance to managers, planners, or political decision-makers from any electrical enterprise to help them find suitable solutions for planning and operation of smart grid projects.

An Intelligent Adaptive Overcurrent Protection System for an Automated Microgrid in Islanded and Grid-Connected Operation Modes

As the penetration of distributed generation sources increases at the distribution level, the necessity of designing microgrids is highlighted. Microgrids can operate in either islanded (separated from the utility grid) or grid-connected mode. Apart from the technical and economic benefits of microgrids, they may cause some protection issues in distribution systems. The most important of these issues is the difference between the short circuit levels in islanded and grid-connected operation modes. In this paper, an intelligent overcurrent relay that can adapt to the microgrid operation mode is proposed; that is, the relay detects the microgrid operation mode by means of an adaptive algorithm. The proposed adaptive method optimizes the accuracy and speed of the algorithm for detecting the microgrid operation mode. Then, the optimal settings that have been already stored in the relay are activated according to the microgrid operation mode. All internal processes of the relay use the voltage and current sampled at the relay location. As a result, the relay can be used in all networks without communication infrastructures. Finally, the proposed method is implemented in a sample microgrid. The superiority of the intelligent relay performance over conventional overcurrent relays is shown by numerical results.

Step-Up Resonant Converter For Induction Motor Drive Applications

A new approach for resonant step-up converter which is connected to hybrid micro grid is discussed in this paper. A micro grid has a local source of supply and loads to function as an electrical network either independently or when connected to a grid.A micro grid can integrate effectively distributed generation sources and renewable generation systems like PV, wind and fuel cell generation systems to the existing distribution system. A hybrid micro grid can be connected to DC and AC grids with the help of power electronic interfaces and manage effective power flow throughout the sub grid. The proposed DC–DC converter can be coupled to a AC-DC micro grid with solar energy and when the system operates in isolated mode battery connected to the DC bus maintain the energy requirement. The key principle of power flow control of these devices helps in increase of system stability. The system is simulated in Matlab/Simulink.

An Anti-Islanding Protection for VSM Inverters in Distributed Generation

Virtual synchronous machine (VSM) technology is an attractive control method for an inverter-based distributed generation (DG) due to having the voltage, and frequency support functionality. Embedding an anti-islanding protection (AIP) scheme with a high accuracy is a requirement for DG inverters due to the safety concern of the personnel, and hazardous operation. This paper presents a novel hybrid AIP scheme for VSM inverters for integration of DG sources into the grid. The main advantage of this AIP scheme is that the proposed scheme can be embedded into the control of the DG inverters without a need of additional part in the hardware of the inverter, and any change in the controller. A detailed modeling of its implementation with the inverter control is presented, and the performance of the AIP scheme is verified by simulations, and experiments. It is shown that the AIP scheme detects the islanding condition successfully, and isolates the inverter from the grid after it experiences an islanding condition.

A Comparative Study of Different Control Algorithm Used in Unified Power Quality Conditioner (UPQC) for Power Quality (PQ) Improvement

Demand for power is on constant increase and it has necessitated the use of alternative energy sources that are discrete in nature and need conversion for utilisation. For this conversion, use of the semiconductor devices is indispensable, which has its own technical challenges and one among them is power quality (PQ). PQ has gained a widespread attention with the increase in penetration level of distributed generation (DG). Integration of DG sources in the grid introduces PQ issues like harmonics, flickers, voltage swells and sags in the system. Unified power quality conditioner (UPQC) is identified to be a reliable and efficient flexible AC transmission systems (FACTS) controller to mitigate the power quality problems. UPQC is based on a hybrid technology that consists of series and shunt inverters connected via a DC link that provide voltage compensation and current compensation. Characteristics of the UPQC are dependent on embedded control algorithm, which ensures proper voltage regulation at DC link and capacitor-voltage equalisation. This paper compares the control algorithms utilised in UPQC for generating reference signals for providing voltage and current compensation, with a special emphasis to total harmonic distortion (THD).

Investigation of Multilevel Inverter for the Next Distributed Generation Using Low-Cost Microcontroller

Nowadays, more research projects have described a converter that is widely used at the distributed generation (DG) level in order to increase the amount of electrical power generation. The converter is known as an inverter when only one DG source is used or as a multi-inverter when several DGs are used. Here, the application of a multilevel inverter with a C2000 microcontroller (Texas Instruments (TI) TMS320F28335 microcontroller), which can be implemented with a current feedback loop, is investigated. This microcontroller acts as a communication interface between MATLAB SIMULINK and the multilevel inverter. Meanwhile, the current control model is modeled in MATLAB for designing the control strategy. It is where the multilevel inverter switches are triggered by using pulse-width modulation (PWM) signals generated by the microcontroller output. At the same time, the proportional integral derivative (PID) current control is used in order to allow the load current to follow the reference current. Based on the results, it can be summarized that the multilevel inverter is a very useful device for the next DG sources when it is combined with current control for load current distribution. From this investigation, it can be seen that in the future DGs could be connected to a multilevel inverter structure, where it will reduce the dependency on filter design and have a more sinusoidal output to the load for different DG power ratings.

Phase Balancing and Reactive Power Support Services for Microgrids

Alternating current (AC) microgrids are expected to operate as active components within smart distribution grids in the near future. The high penetration of intermittent renewable energy sources and the rapid electrification of the thermal and transportation sectors pose serious challenges that must be addressed by modern distribution system operators. Hence, new solutions should be developed to overcome these issues. Microgrids can be considered as a great candidate for the provision of ancillary services since they are more flexible to coordinate their distributed generation sources and their loads. This paper proposes a method for compensating microgrid power factor and loads asymmetries by utilizing advanced functionalities enabled by grid tied inverters of photovoltaics and energy storage systems. Further, a central controller has been developed for adaptively regulating the provision of both reactive power and phase balancing services according to the measured loading conditions at the microgrid’s point of common coupling. An experimental validation with a laboratory scale inverter and a real time hardware in the loop investigation demonstrates that the provision of such ancillary services by the microgrid can significantly improve the operation of distribution grids in terms of power quality, energy losses and utilization of available capacity.

Optimal Capacitor Bank Allocation in Electricity Distribution Networks Using Metaheuristic Algorithms

Energy losses and bus voltage levels are key parameters in the operation of electricity distribution networks (EDN), in traditional operating conditions or in modern microgrids with renewable and distributed generation sources. Smart grids are set to bring hardware and software tools to improve the operation of electrical networks, using state-of the art demand management at home or system level and advanced network reconfiguration tools. However, for economic reasons, many network operators will still have to resort to low-cost management solutions, such as bus reactive power compensation using optimally placed capacitor banks. This paper approaches the problem of power and energy loss minimization by optimal allocation of capacitor banks (CB) in medium voltage (MV) EDN buses. A comparison is made between five metaheuristic algorithms used for this purpose: the well-established Genetic Algorithm (GA); Particle Swarm Optimization (PSO); and three newer metaheuristics, the Bat Optimization Algorithm (BOA), the Whale Optimization Algorithm (WOA) and the Sperm-Whale Algorithm (SWA). The algorithms are tested on the IEEE 33-bus system and on a real 215-bus EDN from Romania. The newest SWA algorithm gives the best results, for both test systems.

REACTIVE POWER CONTROL IN MICRO-GRID NETWORKS USING ADAPTIVE CONTROL

Purpose. Despite their economic and environmental benefits, distributed products in power systems have caused problems in power systems. One of the most important issues in this regard is voltage fluctuations and frequencies in Micro-grids, which depends on several factors, such as variable consumption load and errors in power systems. One of the main challenges associated with the use of Micro-grids is power management among distributed generation sources. Power management plays a pivotal role in numerous Micro-grids and may ensure the stable and improved performance of Micro-grids in the permanent status of the system. The present study aimed to examine the power control in Micro-grids by proposing an adaptive control method along with the PID controller for power management and coordination in Micro-grids. This coordination system operates between production sources and controlling the voltage and frequency levels against the possible disturbances occurring anywhere in the system loop. The results of the simulation of the proposed algorithm in MATLAB software environment exhibited a high success rate (i.e., proper response to the fluctuations in the Micro-grid) and extremely low error rate (i.e., proper reactive power in the grid).

Reliability based optimal DG planning for a meshed distribution network

Distributed generation (DG) sources are becoming more popular nowadays because of their technoeconomic and environmental benefits. These benefits are maximized only when the DG sources are properly planned and installed in the distribution networks. Several studies have been carried out in this field considering various objectives and constraints, for single as well as multiple DG placement and sizing. In this paper, an optimization methodology based on particle swarm optimization is used for the optimal planning of multiple DG sources in a meshed distribution network. The solution consists of the possible DG locations, DG capacities, and its operating power factor. The objectives considered are the improvement of reliability indices namely the system average interruption frequency index and system average interruption duration index, reduction of real power loss, and voltage profile improvement. Unlike other works, reliability evaluation is done considering many realistic constraints and it is used as one of the criteria for DG planning. Reliability indices are evaluated using the encoded Markov cut set algorithm. The real power loss and the voltage index are obtained by means of a simple load flow technique. The stochastic nature of the renewable DG output and the load are taken into account during the reliability evaluation along with islanding probability. The optimal planning of DG sources is done for bus 4 of the Roy billinton test system consisting of seven feeders, 102 nodes, and 106 components. Optimal planning for solar based DG sources is done considering three different load models namely residential, commercial, and mixed load.

Distribution System Restoration With Renewable Resources for Reliability Improvement Under System Uncertainties

Integration of renewable distributed generation (DG) units into distribution networks is gaining widespread popularity. However, uncertainties in generation availability associated with renewable DG units pose a major challenge. These uncertainties should be properly addressed to ensure acceptable system performance and improve customer-side reliability. In this article, the reliability assessment of distribution systems embedded with renewable DG sources has been carried out giving emphasis to system uncertainties and optimal restoration strategies. The uncertainties associated with the power output from renewable resources, time-varying load demand, stochastic prediction errors, and random fault events have been accounted for in the restoration optimization formulation for reliability evaluation. In this article, a parameter-free particle swarm optimization (PSO) technique is applied to address the complexity involved in the formulation. Moreover, a problem-specific encoding scheme is also proposed in conjunction with PSO to ensure optimality.

Fuzzy Controller Based Reserve Management in Hybrid Microgrid for Frequency Regulation

Power quality is a growing concern with sensible and critical loads asking for stringent frequency regulations. The distributed generation sources like Solar Photovoltaic, Diesel Generator, Fuel Cells, and Battery driven Electric Vehicles (BEV) are considered as power sources in the system. For the power-sharing among these generators, a central controller with a novel simple adaptive-additive control strategy is used. Each source has a local controller to regulate the power outputs. This paper presents a Neuro-Fuzzy controller for operating Solar Photovoltaic power at a Limited Power Point while a novel Neuro-Tuned-Fuzzy Controller decides which BEVs to be connected to the microgrid by giving a priority value to each BEV. The simulation results show the coordinated operation of the central and local controllers to regulate the power outputs of the sources was effective to manage reserves and achieve frequency regulation.

Islanding Detection o f Distributed Generat ion In The Presence Of Fault Events With C ritical Load And Non Critical Load

Incredible growth in demand for electricity with reliable, eco-friendly and efficient power has motivated the use of Distributed Generation (DG) all over the world. The problems associated with distributed generation system is unintentional islanding which causes power quality issues in the grid. During islanding operation, renewable energy sources such as solar, wind are used as distributed generation sources, supplies power to the local area. Islanding detection can be divided into remote and local methods; the later method is again classified into passive and active methods. In this paper, Passive technique is used for detecting the islanding condition which is carried out by controlling parameters like voltage and frequency. This is modeled and simulated in MATLAB/Simulink software.

Simultaneous Energy and Reserve Market Clearing with Consideration of Interruptible Loads as One of Demand Response Resources and Different Reliability Requirements of Consumers

Abstract Determining the optimal reserve in power systems is closely related to uncertainties in power generation and risks of outage of supply to consumers. Distributed generation sources such as wind farms are usual reasons for uncertainties in MW production. This uncertainty can be alleviated by providing enough reserve in which demand response (DR) programs can play role of resources for reserve. In an electricity market structure, the mentioned points are usually handled by Independent System Operator (ISO) in energy and reserve markets. This paper deals with the problem of reliability-based reserve management. In the mentioned problem, the DR program in the form of interruptible loads is also considered. A new method is proposed in which ISO settle energy and reserve markets simultaneously while employing the DR in the first stage. In addition, consumers’ requirements of reliability are included by assuming that they have possibility to offer their desired levels of reliability to the ISO. The amount of reserve obtained from market settlement is adjusted based on the different reliability requirements of the consumers and different scenarios of the wind farm operation, in the second stage of the proposed method. Also the cost of the reserve adjustment is fairly allocated to producers and consumers. The proposed method applies stochastic programming formulation and its validity is assessed by the GAMS software. Simulation results show that how amount and cost of reserve could be adjusted to cover power balance, cost of power production and load interruption and required reliability of consumers.

Study of the transients with the loss of field of the synchronous generator in the industrial electric power station

One of the main trends of industrial power engineering today is the need to improve the reliability of power supply of responsible consumers along with the increase of competitiveness of products by reducing cost. These requirements are ensured by the widespread introduction of distributed generation sources. These include mini combined heat and power unit, gas turbine, gas engine and combined-cycle gas turbine power plants. At the same time, such changes significantly complicate both the power supply system and possible modes of operation. One of the possible emergency modes in such networks is the loss of field of the synchronous generator. The admissibility of such a regime is specified by regulatory documents. In such a case this generator goes into asynchronous mode and consumes reactive power from the network. The aim of this work is to study the operation of a synchronous generator for a certain time in the asynchronous mode as a result of a loss of field and to develop measures to ensure the admissibility of such a mode in a complex looped network. An algorithm has been developed for calculating the electromechanical transients of a synchronous generator, taking into account the loss of machine field. Studies are carried out for various operational modes of an industrial power plant, taking into account the initial load of the generator using the KATRAN software package. The calculation results allow determining the generator load with active power, at which the synchronous generator can operate in the asynchronous mode without excitation.

Detecting the Fault Section in the Distribution Network with Distributed Generators Based on Optimal Placement of Smart Meters

Abstract One of the most important issues in employing distribution networks is detecting the fault location in medium-voltage distribution feeders. Due to the vastness of distribution networks and growing distributed generation (DG) sources in this network, detection is difficult with the common methods. The aim of this paper is to present a method based on voltage distributed meters in a medium-voltage distribution network (by smart meters installed along the feeder) in order to detect the fault location in the presence of DG sources. Due to vastness of distribution network and cost of installing smart meters, it is not economically possible to install meters in all the Buses of the network. That’s why in this article, combination of genetic and locating algorithms and fault-based on voltage drop has been used to suggest a method to optimize the meter locations. In order to evaluate the efficiency of the method suggested, first we determine the optimal number and location of the meters and then we apply the fault that has been simulated in different Buses of the sample network, using PSCAD/EMTDC software. After results analysis, the fault location is estimated by MATLAB. Simulation results show that the fault locating method by optimal number of meters has good efficiency and accuracy in detecting faults in different spots and in different resistance ranges.

A Robust Formulation Model for Multi-Period Failure Restoration Problems in Integrated Energy Systems

The risks faced by modern energy systems are increasing, primarily caused by natural disasters. As a new form of multi-level energy complimentary utilization, integrated energy systems are attracting more and more attention for their high-efficiency and low-cost. However, due to the deep coupling relationship between systems, they are more susceptible to natural disasters, resulting in a cascading failure. To enhance the resilience of the integrated electricity-gas system, this paper proposes a failure restoration strategy after a natural disaster occurs. First, the temporal constraints of the dispatching model are considered, and the failure restoration problem is molded into a multi-period mixed-integer linear programme, aiming to recover the interrupted loads as much as possible. Second, since the uncertain output of distributed generation sources (DGs) such as wind turbines and photovoltaic systems will threat the reliability of restoration results, the robust formulation model is incorporated to cope with this problem. Third, we propose a new modeling method for radial topology constraints towards failure restoration. Moreover, the Column and Constraints Generation (C&CG) decomposition method is utilized to solve the robust model. Then, the piecewise linearization technique and the linear DistFlow equations are utilized to eliminate the nonlinear terms, providing a model that could be easily solved by an off-shelf commercial solver. The obtained results include the sequence of line/pipeline switchgear actions, the time-series dispatching results of electricity storage system, gas storage system, and the coupling devices including the gas-fired turbine, power to gas equipment. Finally, the effectiveness of the proposed restoration strategy is verified by numerical simulation on a 13-6 node integrated energy system.

An efficient Mppt approach of PV systems: incremental conduction pathway

<p class="Abstract">Distributed Generation source have wide application due to their phenomenal advantages. These sources include Photovoltaic (PV) cells producing DC voltage at their output that connects the network through a power electronic interface. PV characteristics, on the other hand, illustrate the fact that maximum power can be extracted at the optimal operating point depending upon the solar radiation and ambient temperature. In order to keep the PV module at its optimal operating point, a DC-DC converter is often used between a PV module and inverter. Consequently, Maximum power point trackers (MPPT) grab the foremost position in the efficiency analysis of the global PV system. Among the several MPPT algorithms, Incremental Conduction technique isemphasised upon as it is extremely simple in implementation within electronic programmable circuits. This paper incorporates the MPPT model using a PV module that always works in its optimal operating point. Design and experimental results of a small prototype of MPPT is presented here based on the Simulink model to verify the advantages of proposed integrated system.</p>

Short-Circuit Analysis Models for Unbalanced Inverter-Based Distributed Generation Sources and Loads

Inverter-based distributed generation (IBDG) sources are continually being connected to the grid. Such IBDG sources act as current sources that are unbalanced in either one or two phases. When connected to the grid, unbalanced IBDG sources inject the unbalanced current during an electric fault. Moreover, unbalanced load currents can also change the short-circuit current. Therefore, short-circuit analyses of power systems with either clustered or distributed IBDG sources should not ignore the contribution from unbalanced IBDG sources and load currents. Thus, the objective of this study is to present a method that calculates the short-circuit current flowing from unbalanced IBDG sources. For this purpose, zero- and negative-sequence networks are referred to the positive-sequence network, and new bus impedance matrices are defined for each sequence network. This study also proposes a hybrid method that combines Thevenin's equivalent circuit and the three-phase bus impedance matrix for distribution systems with untransposed lines. The method examines the effect of unbalanced loads on the short-circuit current. The proposed methods are verified by using well known IEEE test feeders.