Distributed Generation Scheme Research Articles

Performance evaluation of solar-PV integrated hybrid fuzzy-logic controlled multi-functional UPQC for enhancing PQ features

To improve distribution system voltage and current quality, a newly built solar-PV system connected multi-functional universal power quality compensator (MFUPQC) has been extensively used. The proposed MFUPQC mitigates both load and source-side concerns in a three-phase distribution system. Furthermore, as part of the distributed generation scheme, active power from solar PV is injected into the grid or source when solar PV is available. In this context, the proposed MFUPQC was tested in both PQ enhancement and DG integration modes using a feasible control scheme. The proportional-integral controller is used for shunt- voltage-source inverter (VSI) DC-link control, which is not suitable for regulating DC-link voltage at the desired level due to incorrect gain value selection. In this work, an intelligent hybrid-fuzzy-logic DC-link control of MFUPQC evidences the intelligent knowledge base for better regulation of power-quality issues. The suggested hybrid fuzzy-logic controlled MFUPQC device's performance for both power quality (PQ) improvement and DG integration is validated using the MATLAB/Simulink software tool, and simulation results are provided with an appealing comparison analysis.

Reduction of electricity cost in public administration through a distributed generation strategy

The use of distributed generation as an alternative to reduce energy costs in the city hall of Vitória, capital of state of Espirito Santo in Brazil, is proposed in this paper. Photovoltaic solar energy was considered and the system sizing was carried out based on the total cost of eletricity in 2016 (available at the City’s Transparency Website), resulting in a system with a total power of 78 MW. The financing scenarios were analyzed for acquisition of the system scaled with a horizon of 25 years. The results of the economic-financial analysis indicate that the investment is advantageous for the municipality and can bring great returns to the society

Novel Bidirectional Four-Port DC–DC Converter Suitable for Bipolar DC Solar Household Integration

The growing focus on increasing renewable energy generation has expanded distributed generation schemes and localized DC grids worldwide. Therefore, DC households are becoming a more prevalent and efficient alternative to their AC counterpart. Even though the bipolar DC grid is more reliable and efficient than the unipolar counterpart, very few works are reported, and there exists scope for improvement. A novel Four-port Converter (FPC) suitable for integrating Renewable Energy Sources (e.g., solar PV), Energy Storage elements (e.g., lead-acid battery), and a bipolar port capable of bi-directional power flow (DC household), is proposed in this paper. This scheme is named Bipolar Boost Four-port Converter (BBFPC) and has inductively interfaced ports capable of handling bi-directional power flow. BBFPC is capable of performing the following functions: (a) Maximum Power Point Tracking (MPPT) for solar PV, (b) over-charge and over-discharge protections for the lead-acid battery, and (c) either voltage regulation of the bipolar port in stand-alone mode or power distribution control of the bipolar port in grid-connected mode. The performance of the BBFPC PV-based bipolar DC system in various operating conditions is analyzed and validated using a 400W prototype.

Harmonic Compensation via Grid-Tied Three-Phase Inverter with Variable Structure I&I Observer-Based Control Scheme

The power inverter topologies are indispensable devices to incorporate distributed generation schemes, like photovoltaic energy sources into the AC main. The nonlinear behavior of the power inverter draws a challenge when it comes to their control policy, rendering linear control methods often inadequate for the application. The control complexity can be further increased by the LCL filters, which are the preferred way to mitigate the current ripple caused by the inverter switching. This paper presents a robust variable structure control for a three-phase grid-tied inverter with an LCL filter. As well to the benefits of the sliding mode control (SMC), which is one of the control methods applied by power converters founded in literature, the proposed control scheme features a novel partial state observer based on the immersion and invariance technique, which thanks to its inherent robustness and speed of convergence is adequate for this application. This observer eliminates the need for physical current sensors, decreasing the overall cost and size, as well as probable sources of noise. The proposed controller is meant for a three-phase grid-tied inverter to inject active power to the grid while harmonics generated by nonlinear loads are compensated. The simulation results prove the effectiveness of the proposed method by compensating for current harmonics produced by the nonlinear loads and maintaining a low total harmonic distortion as recommended by the STD-IEEE519-2014, regardless of whether the system provides active power or not.

Controller Hardware-in-the-Loop Validation of Coordinated Voltage Control Scheme for Distribution Systems Containing Inverter-Based Distributed Generation

This article presents the controller hardware-in-the-loop (CHIL) validation of a novel coordinated voltage control solution for distribution systems with high penetration of distributed generation (DG). The control algorithm coordinates traditional voltage regulation devices and inverter-based DGs capable of supplying reactive power to mitigate voltage violations. Voltage sensitivity analysis and electric distances are used to identify the contributing nodes and the amount of VAR to be injected so that voltage violations can be mitigated. The proposed algorithm is validated using offline simulation and a real-time CHIL setup that considers a real-world communication scenario. In both the offline and real-time validation, a feeder model based on an actual distribution feeder with real field data is used. The results show that the proposed algorithm is successful in coordinating the available system resources to keep the system voltages within the desired limit.

Generation of a fault-tolerant clock through redundant crystal oscillators

Having a precise and stable clock that is still fault tolerant is a fundamental prerequisite in safety critical real-time systems. However, combining redundant independent clock sources to form a unified fault-tolerant clock supply is non-trivial, especially when redundant clock outputs are required – e.g., for supplying the replicated nodes within a TMR architecture through a clock network that does not suffer from a single point of failure. Having these outputs fail independent but still keeping them tightly synchronized is highly desirable, as it substantially eases the design of the overall architecture.In this paper we address exactly this challenge. Our approach extends an existing, ring-oscillator like distributed clock generation scheme by augmenting each of its constituent nodes with a stable clock reference. We introduce the appropriately modified algorithm and illustrate its operation by simulation experiments. These experiments further demonstrate that the four clock outputs of our circuit do not share a single point of failure, have small and bounded skew, remain stabilized to one crystal source during normal operation, do not propagate glitches from one failed clock to a correct one, and only exhibit slightly extended clock cycles during a short stabilization period after a component failure. In addition we give a rigorous formal proof for the correctness of the algorithm on an abstraction level that is close to the implementation.

A Novel Multilevel Inverter with Reduced Number of Switches Using Simplified PWM Technique

Multilevel inverter (MLI) topologies greatly sustained the emergence of modish power-electronic device as an expressive substitute of traditional two-level inverters in the area of medium-voltage high-power energy conversion schemes. It recommends the most outstanding solutions for high-power applications particularly in distributed generation schemes and plays a key role for establishment of novel MLI structures with fewer switching components. This paper proposes the novel 7-level asymmetric MLI topology and administered by both fundamental frequency-based pulse-width modulation (PWM) scheme and advanced multi-carrier PWM scheme. The proposed asymmetric 7-level smart MLI topology offers low switching elements, low gate drive circuits, low cost, minimum space requirement, low-voltage dv/dt switch stress, low switching loss and high efficiency over the traditional topologies. The critical evaluation of proposed 7-level asymmetric MLI performance is verified by MATLAB/Simulink platform and validated through experimental prototype; results are illustrated with proper comparisons.

Interconnection of Hybrid Power System to Grid & Enhance Power Quality Features in DG System using Multilevel STATCOM

The distributed generation scheme with integration of renewable energy sources furnishes the feasible solution to acquire the stable power demand in grid-connected system under sudden load interruptions. Over the various compensation devices, the highly recognized multi-purpose Static Compensator is integrated to grid for attaining enhanced power quality features. A co-generation based grid-integrated renewable sources are used but, the output of these sources are maintained un-constant due to presence of variable source. In this paper, a novel current controller was developed to maintain output of co-generation system as constant and achieve the load demand continuously. But, this scheme has two major disadvantages, primary one is current controller prerequisites the traditional PI controller, which is controlled by intelligent based Fuzzy-Logic controller that is adopted. The second is, the regular 3-level voltage-source inverter is used in STATCOM which has square-wave output voltage requires high range of filter units, more common-mode voltage, high dv/dt stress, more switching losses, low efficiency, so on. These issues are counteracted by utilizing multilevel inverter with attractive modulation scheme. The performance evaluation of proposed Multilevel Inverter based STATCOM is verified by traditional PI and proposed Fuzzy-Logic current controller by using MATLAB/SIMULINK tool and results are conferred with comparisons.

Modelling and analysis of distributed power generation schemes supplying unbalanced and non-linear load

This study presents a combined control strategy for stand-alone distributed power generation scheme, utilizing the squirrel cage induction generator (SCIG), and the permanent magnet synchronous generator (PMSG) in its structure. The combined control consists of both the machine side and load side converter control. The proposed load voltage controller, cascaded with the inner filter current controller, is designed for a load-side converter (LSC) to remove the harmonic component during non-linear loading and negative sequence component in case of unbalanced loading respectively. The control algorithm ensures to produce constant load voltage amplitude and frequency, with the change in both input power and non-linear and unbalanced loading scenarios. It also guarantees the sinusoidal load voltage under the mentioned loading conditions. Simultaneously, the dc-link voltage controller cascaded with the inner q-axis stator current controller is used for machine side converter (MSC) to keep the dc-link voltage at the prescribed level for both SCIG and PMSG during all the operating conditions. In this paper, an analysis of both the distributed generators based wind energy conversion systems under vector control for MSC provides the enhanced machine variable performance. The proposed control scheme is successfully implemented in MATLAB/Simulink environment. One scaled experimental prototype is developed, and real-time results are shown in the paper to validate the theoretical claims of the controllers.

A general coordinated voltage regulation method in distribution networks with soft open points

Due to the high flexibility and fast response capability, power electronic devices are versatile, and increasingly being considered to mitigate voltage violations and improve system efficiency in distribution networks with high penetration of distributed generation (DG). This paper proposes a novel voltage regulation framework in distribution systems through the general types of Soft Open Points (SOPs) and reactive powers of DG inverters. By using the linearized DistFlow equations, we establish a biconvex problem that minimizes voltage deviation via a well-coordinated scheme for SOPs and DGs. The coordination of different types of power electronic devices can be simultaneously modelled into this problem which can be efficiently solved by alternative convex search algorithm. The proposed approach is validated by numerical simulations on modified IEEE 15-bus system, IEEE 33-bus system, and IEEE 69-bus system with different types of power electronic compensators.

Operation in distributed power generation scheme with transition of control between stand-alone and grid connected modes

Operation in distributed power generation scheme with transition of control between stand-alone and grid connected modes

Expanding the Distributed Generation Concept: Toward Decentralized Energy and Water Supply.

Rainwater harvesting decentralizes the water supply in full analogy to what building‐integrated photovoltaics and solar thermal do for electricity and heat. In this new decentralized generation scenario, the built environment is used to collect both sunlight photons and water molecules with significant economic and environmental benefits. Referring to recent progress and to real‐life findings from around the world, this work provides an answer to several relevant questions of direct interest to policy makers and early adopters of broadened distributed generation. The conclusions offer guidelines for developing a successful distributed generation strategy at the regional level by unifying solar energy and water management policies.

Real-Time Fuzzy Voltage Regulation for Distribution Networks Incorporating High Penetration of Renewable Sources

This paper proposes a coordinated voltage regulation scheme for on-load tap changer (OLTC) and renewable distributed generation (DG) units to provide a proper voltage regulation for active distribution systems. The main motivation of applying fuzzy logic is that it can deal with environments of imperfect information, and thus, it can reduce communication requirements. The proposed regulation scheme consists of three fuzzy-based control algorithms. The first control algorithm is proposed for the OLTC such that it can mitigate the effect of DG units on the voltage profile. The second control algorithm is proposed to provide a DG reactive power sharing, in order to relax the OLTC tap operation. The third control algorithm aims to partially curtail DG active powers to restore a feasible solution from the OLTC prospective. The proposed fuzzy algorithms have the advantage of providing proper voltage regulation with relaxed tap operation, utilizing only the estimated system minimum and maximum voltages. Moreover, it avoids numerical instability and convergence problems associated with centralized approaches, as it does not require to run an optimization algorithm. Real-time simulations are developed to show the effectiveness of the proposed fuzzy algorithms on a typical distribution network, using OPAL-RT real-time simulator.

A Critical Evaluation of Power Quality Features using Dual APF under Grid Interfaced DG Scheme

This paper presents the concept of power quality enhancement reducing the harmonic distortion with power distribution system consisting of balanced and unbalanced non-linear type of loads. This paper presents power quality enhancement using dual active power filters (APF’s) under grid connected distributed generation scheme. Acive power filters effectively generate compensating signals for harmonic abolition and this paper presents APF for compensating currents to be induced in to distribution grid for harmonic elimination under balanced and unbalanced non-linear load conditions. Distributed generation (DG) feeds the grid and the scheme of grid interfaced DG was explained. APF is controlled using instantaneous P-Q theory and DG inverter is controlled using simple control strategy. Proposed system was developed and the results are obtained using MATLAB/SIMULINK software.

Current tidal power technologies and their suitability for applications in coastal and marine areas

A considerable body of research is currently being performed to quantify available tidal energy resources and to develop efficient devices with which to harness them. This work is naturally focussed on maximising power generation from the most promising sites, and a review of the literature suggests that the potential for smaller scale, local tidal power generation from shallow near-shore sites has not yet been investigated. If such generation is feasible, it could have the potential to provide sustainable electricity for coastal homes and communities as part of a distributed generation strategy, and would benefit from easier installation and maintenance, lower cabling and infrastructure requirements and reduced capital costs when compared with larger scale projects. This article reviews tidal barrages and lagoons, tidal turbines, oscillating hydrofoils and tidal kites to assess their suitability for smaller scale electricity generation in the shallower waters of coastal areas at the design stage. This is achieved by discussing the power density, scalability, durability, maintainability, economic potential and environmental impacts of each concept. The discussion suggests that tidal kites and range devices are not well suited toward small-scale shallow water applications due to depth and size requirements, respectively. Cross-flow turbines appear to be the most suitable technology, as they have high power densities and a maximum size that is not constrained by water depth. Oscillating hydrofoils would also be appropriate, provided comparable levels of efficiency can be achieved.

Aplicación de los sistemas fotovoltaicos conectados a la red: estado del arte

En este trabajo se describen todos los conceptos necesarios para lograr implementar un sistema fotovoltaico como alternativa para ser utilizado como generador distribuido. Para ello, se realiza un pequeño estado del arte en el cual se manejan conceptos básicos, desde el funcionamiento de una celda solar hasta conceptos de redes inteligentes aplicados en la gestión de la demanda. Asimismo, se abarca un repaso sobre los marcos regulatorios existentes en Colombia, donde se habla de generación distribuida debido a la falta del mismo. Es necesario comparar tales regulaciones con los diferentes marcos regulatorios existentes en otros países, como Alemania, España y EE.UU., para obtener un modelo de trabajo idóneo. Finalmente, se decide utilizar un generador fotovoltaico conectado a la red de baja tensión como alternativa en los sistemas de generación distribuida, ya que con estos se pueden realizar balances energéticos, esto en caso de que en el país en donde se emplee esta alternativa no se tenga establecido un marco regulatorio adecuado, de manera que el usuario no tenga problemas con las entidades regulatorias actuales.

Wind Energy System and Efficient Deployment in Owerri via Distributed Generation Scheme

Wind energy is one of the fastest growing technologies in the energy generation industry nowadays. The erratic and epileptic state of power supply in Nigeria resulting from insufficient generation to meet the load demands, and issues about global warming is of great concern to all. This has led to load shedding; blackout in some parts of the country lasting for hours, closure of some industries due to high operational cost. However the nation is currently diversifying its power generation capabilities through distributed generation using renewable resources. In order to ameliorate the situation, and to curb the global warming challenge, deployment of distributed generation (DG) using wind for electricity generation has become a novel idea. This is so because wind is abundantly available for all hours of the day and the resource is environmentally friendly. This paper therefore evaluated the wind energy potential of Owerri using the available data; considered how best it could be utilized to generate electricity through stand alone scheme and integration with the utility grid for most efficient operation.

A review of voltage dip mitigation techniques with distributed generation in electricity networks

The advent of power quality sensitive equipment has made the provision of good power quality a real challenge across the globe. With the increasing usage of sophisticated sensitive electronic equipment in industrial, residential and commercial sectors, it is important to protect them from any power quality disturbance in order to avoid equipment damage and malfunction leading to financial loss for the customer. Voltage quality disturbances such as voltage dips pose a serious concern as a power quality problem, since due to their stochastic nature they cannot readily be eliminated from regular utility systems. However, they can be mitigated. High degree of penetration of distributed generation in power networks is useful in delivering different benefits to the utility in the form of ancillary services one of which is voltage dip mitigation in case of system contingencies. This paper presents a comprehensive review and comparison of various distributed generation schemes used by utilities for mitigation of voltage dips in power networks.

A user-mode distributed energy management architecture for smart grid applications

Future smart grids will require a flexible, observable, and controllable network architecture for reliable and efficient energy delivery under uncertain conditions. They will also necessitate variability in distributed energy generators and demand-side loads. This study presents a tree-like user-mode network architecture responding to these requirements. The approaches presented for the next-generation grid architecture facilitate the management of distributed generation strategies based on renewable sources, distributed storage, and demand-side load management.The authors draw a framework for the future digital power grid concept and assess its viability in relation to volatile, diverse generation and consumption possibilities. In this sense, probabilistic energy balance analyses of tree-like user-mode networks with a stochastic end-user population are conducted to investigate the energy reliability of the proposed grid. A case study based on published generation and consumption profile data is also presented, and several generation scenarios formed by variants of this data are discussed.

Lab-Scale TCR-Based SVC System for Educational and DG Applications

Motivated by the development of power semiconductor technologies, flexible ac transmission systems (FACTS) devices and their penetration in the field of electrical power systems, an educational challenge in complementing theoretical knowledge with practical experience is recognized. In this paper, the design and implementation of a lab-scale hardware and software setup is presented. Three small-scale devices, including a static VAr compensator (SVC) unit, a transmission line model, and a substation, are developed. The SVC unit is validated by obtaining its operating characteristic. The lab setup is presented as a platform to carry out different experiments related to the SVC operation. Safety considerations in the design are discussed. Steady-state and dynamic analysis are presented showing the consistency between theory and practice. The potential use of small SVC units on low-voltage distributed generation schemes is discussed.