Showing papers in "Iet Renewable Power Generation in 2016"
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TL;DR: In this paper, the authors comprehensively review various research works on the technical, environmental and economic benefits of renewable DG integration such as line-loss reduction, reliability improvement, economic benefits and environmental pollution optimisation.
Abstract: Recent advances in renewable energy technologies and changes in the electric utility infrastructures have increased the interest of the power utilities in utilisation of distributed generation (DG) resources to generate electricity. The recent trends in the development and utilisation of DG resources for power generation application are subject to the deregulation of the electric power sector and technical constraints to extend distribution and transmission networks to some areas. The electric power system planners, regulators and the policy makers have derived many benefits from integration of DG units into the distribution networks. These benefits depend on the characteristics of DG units such as photovoltaic (PV), wind system and reciprocating engines, characteristics of the loads, local renewable resources and network configuration. This study comprehensively reviews various research works on the technical, environmental and economic benefits of renewable DG integration such as line-loss reduction, reliability improvement, economic benefits and environmental pollution optimisation. These benefits can be optimised if all the renewable DG units are optimally sized, located and configured. This study also reviews the current status of renewable DG technologies based on different characteristics and the operational issues of integration of renewable DG into the electric power systems.
420 citations
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TL;DR: In this article, an enhancement is introduced to the Inc.Cond algorithm in order to entirely eliminate the division calculations involved in its structure, thus, algorithm implementation complexity is minimised enabling the utilisation of low-cost microcontrollers to cut down system cost.
Abstract: Variable-step incremental conductance (Inc.Cond.) technique, for photovoltaic (PV) maximum power point tracking, has merits of good tracking accuracy and fast convergence speed. Yet, it lacks simplicity in its implementation due to the mathematical division computations involved in its algorithm structure. Furthermore, the conventional variable step-size, based on the division of the PV module power change by the PV voltage change, encounters steady-state power oscillations and dynamic problems especially under sudden environmental changes. In this study, an enhancement is introduced to Inc.Cond. algorithm in order to entirely eliminate the division calculations involved in its structure. Hence, algorithm implementation complexity is minimised enabling the utilisation of low-cost microcontrollers to cut down system cost. Moreover, the required real processing time is reduced, thus sampling rate can be improved to fasten system response during sudden changes. Regarding the applied step-size, a modified variable-step size, which depends solely on PV power, is proposed. The latter achieves enhanced transient performance with minimal steady-state power oscillations around the MPP even under partial shading. For proposed technique's validation, simulation work is carried out and an experimental set up is implemented in which ARDUINO Uno board, based on low-cost Atmega328 microcontroller, is employed.
175 citations
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TL;DR: In this article, a flexible power controller is developed in the PV inverter and flexibly change from one to another mode during operation, based on the single-phase PQ theory, the control strategy offers the possibilities to generate appropriate references for the inner current control loop.
Abstract: This study explores the integration issues of next-generation high-penetration photovoltaic (PV) systems, where the grid is becoming more decentralised and vulnerable. In that case, the PV systems are expected to be more controllable with higher efficiency and reliability. Provision of ancillary and intelligent services, such as fault ride-through and reactive power compensation, is the key to attain higher utilisation of solar PV energy. Such functionalities for the future PV inverters can contribute to reduced cost of energy, and thus enable more cost-effective PV installations. To implement the advanced features, a flexible power controller is developed in this study, which can be configured in the PV inverter and flexibly change from one to another mode during operation. Based on the single-phase PQ theory, the control strategy offers the possibilities to generate appropriate references for the inner current control loop. The references depend on system conditions and also specific demands from both system operators and prosumers. Besides, this power control strategy can be implemented in commercial PV inverters as a standardised function, and also the operation modes can be achieved online in predesigned PV inverters. Case studies have verified the effectiveness and flexibilities of the proposal to realise the advanced features.
145 citations
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TL;DR: In this article, the main challenges facing grid-connected photovoltaic power systems without galvanic isolation are described, and a review of the state-of-the-art of single-phase systems is carried out.
Abstract: Photovoltaic (PV) power systems have been in the spotlight of scientific research for years. However, this technology is still undergoing developments, and several new architectures are proposed each year. This study describes the main challenges facing grid-connected PV systems without galvanic isolation, then carries out a review of the state-of-the-art of single-phase systems. The converter topology review is focused on the match between the different types of converters and the different PV panel technologies, determined by the common-mode voltage between the PV string terminals and the ground. The ground leakage current, due to time variations of this voltage, is a source of electric safety and electromagnetic interference (EMI)-related problems, and its amplitude is constrained by international standards. The basic principles of operation of the different solutions are described, along with their strengths and drawbacks. Conversion efficiency is evaluated qualitatively comparing the semiconductor power losses. Finally, the future trends regarding semiconductor devices, PV panels and international regulations for single-phase grid-connected equipment are discussed, and indications on how these might steer future research efforts in PV converters are inferred.
143 citations
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TL;DR: In this paper, the authors provide the rationale for forecasting in power systems, a succinct review of forecasting techniques as well as an assessment of their performance as applied in the literature, also techniques for improving the accuracy of forecasts have been presented together with key forecasting issues and developing trends.
Abstract: Power generation from renewable energy resources is on the increase in most countries, and this trend is expected to continue in the foreseeable future. In an effort to enhance the integration of renewable power generation from solar and wind into the traditional power network, there is need to address the vulnerabilities posed to the grid as a result of the intermittent nature of these resources. Variability and ramp events in power output are the key challenges to the system operators due to their impact on system balancing, reserves management, scheduling and commitment of generating units. This has drawn the interest of utilities and researchers towards developing state of the art forecasting techniques for forecasting wind speeds and solar irradiance over a wide range of temporal and spatial horizons. The main forecasting approaches employ physical, statistical, artificial intelligence and hybrid methodologies. This study provides the rationale for forecasting in power systems, a succinct review of forecasting techniques as well as an assessment of their performance as applied in the literature. Also, techniques for improving the accuracy of forecasts have been presented together with key forecasting issues and developing trends.
131 citations
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TL;DR: In this paper, the authors presented an optimal sizing methodology for a stand-alone and grid connected PV-biomass hybrid energy system that serves the electricity demand of a typical village.
Abstract: This study presents an optimal sizing methodology for a stand-alone and grid connected PV-biomass hybrid energy system that serves the electricity demand of a typical village. However, this method is scalable and can be used in any test system. A recently developed artificial bee colony (ABC) algorithm is used to detect out the optimum hybrid system configuration with the least levelised cost of energy while minimising annualised cost of the system. It has been observed from the results that a grid connected hybrid PV-biomass system is cost effective and reliable choice for rural electrification as compared with stand-alone hybrid PV-biomass energy system. It has been emerged from this study that the proposed system offers reliable and affordable electricity in a sustainable way by harnessing locally available natural resources. A brief comparison of results obtained from the ABC algorithm and hybrid optimisation model for electric renewable (HOMER) has been carried out. Moreover, it is also observed from the results that the ABC algorithm provides better results as compared with HOMER.
129 citations
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TL;DR: In this article, the authors proposed a control strategy to compensate the lack of short-term frequency response ability of wind farms (WFs) by the energy storage system (ESS), which is installed at the point of common coupling of the WF to make it have similar shortterm frequency respond ability to that of synchronous generators, and a fuzzy logic controller is designed for the ESS so that the required rated power of the Ess could reach its theoretical minimum value as closer as possible.
Abstract: The increasing high penetration of wind power is bringing a serious challenge to the frequency regulation of power system, for wind turbine generators are unable to naturally contribute to system frequency response. To address this problem, this study proposes a control strategy to compensate the lack of short-term frequency response ability of wind farms (WFs) by the energy storage system (ESS). First, the rated power and capacity of the ESS, which is installed at the point of common coupling of the WF to make it have similar short-term frequency response ability to that of synchronous generators, are determined. The theoretical minimum rated power of the ESS should be about 5% rated power of the WF, only if the active power output of the ESS is controlled as its rated power during the whole inertial response process. Then, a fuzzy logic controller is designed for the ESS so that the required rated power of the ESS could reach its theoretical minimum value as closer as possible. Simulation results of a simplified practical power system show that WFs with the proposed strategy could response to the frequency change rapidly and support short-term frequency control effectively under various disturbances.
129 citations
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TL;DR: In this article, a stochastic planning framework for the battery energy storage system (BESS) in distribution networks with high wind power penetrations was proposed, aiming to maximise wind power utilisation while minimise the investment and operation costs.
Abstract: In recent years, the battery energy storage system (BESS) has been considered as a promising solution for mitigating renewable power generation intermittencies. This study proposes a stochastic planning framework for the BESS in distribution networks with high wind power penetrations, aiming to maximise wind power utilisation while minimise the investment and operation costs. In the proposed framework, the uncertainties in wind power output and system load are modelled by the Monte-Carlo simulation, and a chance-constrained stochastic optimisation model is formulated to optimally determine the location and capacity of BESS while ensuring wind power utilisation level. Then, the Monte-Carlo simulation embedded differential evolution algorithm is used to solve the problem. Simulation studies performed on a 15-bus radial distribution system prove the efficiency of the proposed method.
124 citations
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TL;DR: In this article, the authors investigated the performance of the incremental conductance (INC) algorithm at high perturbation frequencies, when the system response to MPPT perturbations is never allowed to settle.
Abstract: One of the most commonly utilised maximum power point tracking (MPPT) algorithms for photovoltaic (PV) generators is the incremental conductance (INC) algorithm. Yet, the operating characteristics of this algorithm at high perturbation frequencies, when the system response to MPPT perturbations is never allowed to settle, have not been addressed in the literature. This study characterises system behaviour in this operating mode experimentally for a standalone PV system with a dc motor–pump load. Results show that the INC algorithm operating at a high perturbation rate offers higher energy utilisation efficiency and better system performance despite the resulting non-periodic waveforms of the system.
106 citations
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TL;DR: In this paper, the impact of the inertia reduction due to wind and photovoltaic (PV) power electronics interface on frequency stability indicators, such as the rate of change of frequency and the frequency nadir following a large generation loss, is assessed.
Abstract: This study addresses the development and operation of the European continental electricity system with a high penetration of wind and photovoltaic (PV) generation. The main focus of the work is the assessment of the impact of inertia reduction, due to wind and PV power electronics interface, on frequency stability indicators, as the rate of change of frequency and the frequency nadir following a large generation loss. The analysis is based on dynamic frequency stability studies, performed for every hour of the year and over a large number of weather scenarios. The outputs of these simulations are used to perform statistical analysis of these indicators and to estimate the critical instantaneous penetration rate of wind and PV, which the European continental synchronous area can accommodate from a system dynamics point of view. The results show that a single critical instantaneous penetration rate cannot be defined, since the frequency dynamic behaviour depends on parameters that change from one period to the following. Instead, this critical penetration rate should be calculated for every dispatch period. This study also highlights the growing importance of load self-regulating effect's contribution to frequency stability in the future system.
104 citations
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TL;DR: In this paper, the authors modelled and analyzed transient and small-signal stability for a representative transmission system with realistic loading scenarios and high PV penetration levels, and implemented a positive-sequence dynamic model of a utility-scale PV unit (USPVU) in the open programming environment MATLAB/Simulink.
Abstract: Photovoltaic (PV) systems are gradually replacing conventional synchronous generators. However, reduced system inertia and lack of dynamic grid support from PV are the main issues that could have a detrimental impact on the transient response in power systems when critical contingencies arise. In this study, the authors modelled and analysed transient and small-signal stability for a representative transmission system with realistic loading scenarios and high PV penetration levels. First, system eigenvalues were calculated to identify critical modes. Thereafter, the results of the small-signal analysis were further expanded by performing transient simulations after critical contingencies. Such contingencies detrimentally excited the critical modes of the system. To carry out this analysis, they implemented a positive-sequence dynamic model of a utility-scale PV unit (USPVU) in the open programming environment MATLAB/Simulink. This dynamic model is based on a Western Electricity Coordinating Council (WECC) generic model (full converter model), which is suitable for electromechanical transient studies. Also included was the model of the PV array, dc-dc converter, and associated control systems. The most critical factors pertaining to the detrimental or beneficial impact of USPVUs on stability were the unit commitment and dispatch strategy and the protection/control strategy during voltage swell and dip events for equivalent PV penetration and loading scenarios.
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TL;DR: This study proposes a two-stage operational planning framework for the short-term operation of the virtual power plant (VPP), and a model predictive control-based dispatch model is proposed to optimise the real-time control actions.
Abstract: This study proposes a two-stage operational planning framework for the short-term operation of the virtual power plant (VPP). In the first stage, a stochastic bidding model is proposed for the VPP to optimise the bids in the energy market, with the objective to maximise its expected economic profit. The imbalance costs of the VPP are considered in the bidding model. In the second stage, a model predictive control (MPC)-based dispatch model is proposed to optimise the real-time control actions. In the real-time dispatch model, the real-time information of the resources is continuously updated, and the deviations between the actual energy output and the contracted energy over the MPC control horizon are minimised. The simulation results prove the efficiencies of the proposed method.
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TL;DR: In this article, a comprehensive harmonic behavior analysis has been performed on the IEEE-13 bus distribution network with high PV systems penetration, where a certain level of harmonics is also injected into the IEEE network through nonlinear loads to resemble a realistic scenario.
Abstract: Solar photovoltaic (PV) system installations are rapidly increasing in distribution networks. These PV systems include power electronic devices which have an influence on the power quality of the grid in the form of harmonic distortion. The aim of this study is the harmonic impact of PV systems on distribution networks. A comprehensive harmonic behaviour analysis has been performed on the IEEE-13 bus distribution network with high PV systems penetration. A certain level of harmonics is also injected into the IEEE network through non-linear loads to resemble a realistic scenario. The investigation has been carried out through simulations of three case studies, namely PV system integrations at a single node in particular with and without the presence of background distortions in the supply and finally PV penetration at multiple nodes with supply distortions. Furthermore, an evaluation study has been conducted at the University of Queensland PV site to validate simulation results. This study has highlighted the PV systems harmonic contributions on real distribution networks and the impact of harmonics propagation on transformer K-factor. Results show that the total harmonic distortions of current and voltage are exceeding the limits when the number of PV systems increases, leading to transformer overloading and heating.
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TL;DR: In this article, a review of grid-tied architectures used in photovoltaic power systems, classified by the granularity level at which maximum power point tracking (MPPT) is applied, is presented.
Abstract: This study provides review of grid-tied architectures used in photovoltaic power systems, classified by the granularity level at which maximum power point tracking (MPPT) is applied. Grid-tied PV power systems can be divided into two main groups, namely centralized MPPT (CMPPT) and distributed MPPT (DMPPT). The DMPPT systems are further classified according to the levels at which MPPT can be applied, i.e. string, module, submodule, and cell level. Typical topologies for each category are also introduced, explained and analyzed. The classification is intended to help readers understand the latest developments of grid-tied PV power systems and inform research directions.
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TL;DR: In this paper, a generalised approach is proposed to model network upgrade deferral as a function of load growth rate, renewable generation penetration and peak shave fraction, which benefits from multi-period power flow analysis to co-optimise battery size, location, charge/discharge profile for a pre-specified number of units to be deployed in a given distribution network.
Abstract: Prompted by technical issues that have arisen due to the widespread deployment of distributed intermittent renewable generators, rapidly rising peak demand and reductions in battery price, the use of battery-based energy storage systems in power networks is on the rise. While battery-based energy storage has the potential to deliver technical benefits, the best possible sizing, location and usage govern the financial viability. The objective of this study is twofold. Firstly, a generalised approach is proposed to model network upgrade deferral as a function of load growth rate, renewable generation penetration and peak shave fraction. This model is then used for the formulation of an optimisation problem which benefits from multi-period power flow analysis to co-optimise battery size, location, charge/discharge profile for a pre-specified number of units to be deployed in a given distribution network. The proposed approach is implemented using the generic algebraic modelling system platform and validated on an Australian medium voltage distribution network under multiple practical and potential future scenarios.
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TL;DR: In this paper, the authors presented a wind-solar photovoltaic based standalone hybrid energy system (HES) for an unelectrified village for central region of India - Madhya Pradesh.
Abstract: This study presents a wind-solar photovoltaic based standalone hybrid energy system (HES) for an un-electrified village for central region of India - Madhya Pradesh. The inputs for the designing of HES are wind speed, solar radiation, temperature and the load demand which are variable with respect to time. In this study, hourly values of meteorological data and hourly load demand are considered over a year. For sizing and performance analysis of this standalone HES, ant colony optimisation technique has been used. The performance analysis of the system is done for the various parameters such as total cost of the system, power generated by various sources, state of charge of battery, contribution of various sources, continuity of supply to the load demand and unmet load. The obtained optimal configuration of the proposed HES is found to provide minimal energy cost with excellent performance and reduced unmet load.
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TL;DR: In this article, the authors assess two years of operational experience with inertial response provided by type 4 wind turbines installed in a 138 MW wind farm in the Canadian province of Quebec.
Abstract: The need for inertial response provided by wind turbines (WTs) has been discussed in the industry for more than five years now. Yet, as of today only very few grid codes include specific requirements. Hence, the number of wind farms in commercial operation using such frequency control features is low, and knowledge of the real capabilities and limitations of inertial response from WTs is limited. The objective of this article was to summarise and to assess two years of operational experience with inertial response provided by type 4 WTs installed in a 138 MW wind farm in the Canadian province of Quebec. In order to put the topic into context, existing and anticipated future grid code requirements in respect to inertial response as well as related performance criteria were summarised. Data from high-frequency measurement devices recorded at various operating conditions and grid situations was downloaded and processed. The actual performance was compared with the expected characteristics for each of the measurements, which allowed identifying areas for further development. Results of dynamic simulations demonstrated that the methodology and the models used for frequency control studies need to be improved.
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TL;DR: In this paper, a lowvoltage ride through (LVRT) scheme for the permanent magnet synchronous generator (PMSG) variable speed wind turbine at grid faults is proposed, where the machine side converter controller is used to control the dc-link voltage using interval type-2 fuzzy logic control.
Abstract: Increased penetration level of the wind power generation has brought new issues and challenges of power quality. One of these issues is low-voltage ride through (LVRT). This study proposes an LVRT scheme for the permanent magnet synchronous generator (PMSG) variable speed wind turbine at grid faults. The machine side converter controller is used to control the dc-link voltage using interval type-2 fuzzy logic control taking into account the non-linear relationship between the generator speed and the dc-link voltage. Under grid faults, there is a power mismatch between the generated active power and the active power delivered to the grid. This excess power is stored in the generator inertia to keep the dc-link voltage constant. To validate the proposed control strategy, simulation results for 1.5 MW PMSG-based wind energy conversion system are carried out by MATLAB-Simulink under symmetrical and asymmetrical faults.
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TL;DR: In this article, a thermophysics-based method for wind turbine drivetrain fault diagnosis is presented, where a synthesised thermal model is formed by incorporating thermal mechanisms of the drivetrain into a WT system model.
Abstract: Cost-effective wind turbine (WT) diagnosis using supervisory control and data acquisition (SCADA) data is a promising technology for future intelligent wind farm operation and management. This study presents a thermophysics-based method for WT drivetrain fault diagnosis. A synthesised thermal model is formed by incorporating thermal mechanisms of the drivetrain into a WT system model. Applications of the model are demonstrated in case studies of the gearbox and generator comparing simulation results and SCADA data analysis. The results show non-linearity of the gearbox oil temperature rise with wind speed/output power that can effectively indicate gearbox efficiency degradation, which may be attributed to gear transmission problems such as gear teeth wear. Electrical generator faults such as ventilation failure and winding voltage unbalance will cause changes to heat transfer and result in temperature changes that can be used for diagnosis purposes. This is shown by different patterns of stator winding temperature associated with power generation, while the simulation reveals the thermal mechanism. The method can be applied to diagnose some failure modes which are hard to identify from vibration analysis. The developed thermal model can play a central role for the purpose of fault diagnosis, by deriving relationships between various SCADA signals and revealing changes in the thermophysics of WT operation.
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TL;DR: In this paper, a set of methodologies to assess the reliability of power distribution network with the penetrations of battery energy storage system (BESS) and intermittent distribution sources is proposed. And the model of MBESS is developed based on the real operation data.
Abstract: The development of battery energy storage system (BESS) facilitates the integration of renewable energy sources in the distribution system. Both distribution generation and mobile BESS (MBESS) can enhance the reliability of the distribution system. MBESS can facilitate the island operation of microgrids. This study proposes a set of methodologies to assess the reliability of power distribution network with the penetrations of MBESS and intermittent distribution sources. First, an analytic approach based on Markov models is applied for assessing the reliability analysis of the MBESS in distribution system. Then the method is verified by Monte Carlo simulation method and extended to a more complex distribution system. The model of MBESS is developed based on the real operation data. Case study on the IEEE test system has successfully verified the effectiveness of the proposed approach.
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TL;DR: In this paper, the authors proposed an optimal rating and location of static synchronous compensator (STATCOM) for enhancing transient voltage stability of a real distribution network with wind power generation.
Abstract: This study proposes optimal rating and location of static synchronous compensator (STATCOM) for enhancing transient voltage stability of a real distribution network with wind power generation. The test network consists of fixed and variable speed wind turbines connected to a rural load centre. To ensure reliable and secure operation of the grid, the wind farm (WF) has to comply with the grid code for its low-voltage ride through operation. Loads play significant role in voltage stability analysis. Induction motors and general loads are modelled according to real-time data available with the system operator. In this study, dynamic reactive power requirement of WFs is considered for determination of rating of the STATCOM. Reactive power margin (Q margin) of load bus is used as an index to identify the location of the STATCOM. Extensive simulation has been carried out in DIgSILENT to show the validity of the proposed approach.
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TL;DR: In this paper, a second-order circulating current injection method based on closed-loop control is proposed to solve the low voltage ride-through (LVRT) problem in an MMC WECS.
Abstract: Traditional low voltage high power wind energy conversion system (WECS) requires heavy cables and large step-up grid interfacing transformers. In recent years, power rating of offshore wind turbines already exceeds 10 MW, and medium voltage (MV) converters have become strongly demanded. Modular multilevel converter (MMC) is suitable for MV high power applications. However, there are two technical difficulties for MMC when applied in MV permanent magnet synchronous generator (PMSG) WECS. The first one is the large sub module (SM) voltage fluctuation caused by low frequency and high amplitude PMSG phase current. The other one is the low voltage ride through (LVRT) problem. Overall control strategy based on carrier-phase-shifted -sinusoidal pulse width modulation technique of the MMC WECS is proposed. For the first difficulty mentioned, a second-order circulating current injection method based on closed-loop control is proposed. For the LVRT problem, a distributed braking chopper solution is provided. The effectiveness of the injection method and the distributed braking chopper solution are validated by simulation of a 5 MW/3.3 kV MMC WECS. Influences of the current injection amplitude on SM voltages and arm currents are discussed and a trade-off method is given to optimise system design, which is also verified by simulation.
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TL;DR: In this article, the application of dish-Stirling solar thermal system (DSTS) in automatic generation control (AGC) of an unequal two area thermal system is discussed.
Abstract: The present study emphasises the application of dish-Stirling solar thermal system (DSTS) in automatic generation control (AGC) of an unequal two area thermal system. The thermal systems are equipped with single reheat turbine, generation rate constraint, and governor dead band. The system dynamics with and without DSTS are tested for integral, proportional integral, proportional integral derivative, and three degree of freedom proportional integral derivative (3DOF-PID) as secondary controllers. The simultaneous optimisation of the controller parameters for each controller is done with biogeography based optimisation (BBO) technique. The 3DOF-PID controllers for the system having DSTS outperform the other controllers in terms of magnitude of oscillation, peak deviation, and settling time in system dynamic responses. The same is validated with random load perturbation. Sensitivity analysis proves that BBO optimised 3DOF-PID controller parameters obtained at nominal conditions are healthy enough. These optimised 3DOF-PID controller parameters are not necessarily needed to optimise for wide changes in system loading, and inertia constant H; step load perturbation (SLP) in all areas and higher SLP in area1. Integration of DSTS for AGC of thermal system is safely attributed.
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TL;DR: In this article, the authors analyzed the parameter design problem of several important elements in the main circuit of the modular multilevel converter (MMC), such as the link transformer, the arm reactor, the sub-module (SM) capacitor and the SM power electronic devices.
Abstract: The modular multilevel converter (MMC) will be used in power systems more and more widely. The main circuit parameter design of the MMC impacts the initial investment and the operating performance of the system. In this study the parameter design problem of several important elements in the main circuit of the MMC, such as the link transformer, the arm reactor, the sub-module (SM) capacitor and the SM power electronic devices are analysed. Based on the fundamental equivalent circuit of the MMC, the design method for the rated valve side no-load voltage of the link transformer is proposed; and the variation range of the rated valve side no-load voltage is determined as (1.00-1.05)/2 times of the DC side voltage. By introducing the concept of the equivalent capacity discharging time constant H
, the nearly constant relationship between the fluctuation ratio of the SM capacitor voltage and the H
-value for different projects is discovered, which means the H
-value is independent of particular projects. In this study, the corresponding parameters of several practical projects are analysed and the recommended H
-value is given as 40 ms. The voltage and current stress of the SM power electronic devices is investigated for the four extreme operating conditions by the analytical formulae of the MMC; and it is discovered that the current stress of the SM power electronic devices changes greatly with the operating condition. By introducing the concepts of the phase unit series resonance frequency and the circulating current resonance frequency, the principle for designing the parameter of the arm inductor is established. Through analysing the corresponding parameters of several real projects, the recommended value of the phase unit series resonance frequency is given as the rated frequency of the connected AC system.
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TL;DR: In this paper, a fuzzy logic controller for individual pitch control (IPC) of a wind turbine was designed in order to optimize a trade-off among several control objectives such as blade root moment and generator torque.
Abstract: With the increasing size of modern large wind turbine (WT), the effects of dynamic loading on the structures become an important influence factor. There are mitigation measures for WT control systems to reduce these imbalance structural loads and regulate power. It has motivated the development of blade individual pitch control (IPC) methodologies. This study focuses on the design of fuzzy logic controller (FLC) for IPC. The controllers are designed in order to optimise a trade-off among several control objectives such as blade root moment and generator torque. Three different FLC had been used in the controllers, the first one related to blade pitch angle and electromagnetic torque control variables to meet specified objectives for operation region, the second control model and the third model related to d-q axis blade moment in non-rotating frame of reference. Likewise, the optimisation criteria of FLC consider for each controller objective to mitigate fatigue loads and regulate output power. Finally, the effectiveness of proposed method is verified by simulation results for three-bladed NREL 2 MW WT. The results proved that the fatigue loads in the turbine are reduced obviously.
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TL;DR: In this paper, the authors used an iterative algorithm to solve the power flow problem in radial grids and considered three methods for the correction of unacceptable overvoltages, which are based on different principles.
Abstract: This study deals with the overvoltage problems caused by the increased photovoltaic (PV) penetration in typical rural radial distribution systems, where small PV systems and household consumers are connected. For this study, the authors used an iterative algorithm to solve the power flow problem in radial grids and considered three methods for the correction of unacceptable overvoltages, which are based on different principles. The system under consideration is an almost symmetrical three phase, low-voltage radial network, consisting of nine PV and consumer connection points. The system was simulated for a whole year with a sample time of 15 min, taking into account the variations of the solar radiation and loads. The results verified that the control of reactive power on the line can successfully manage overvoltage issues. The additional demand of reactive power and consequent line losses are used to evaluate various correction methods.
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TL;DR: In this paper, a linear weighted summation algorithm based on variable weights is proposed to solve the multi-objective optimisation problem to obtain current reference of supercapacitor and battery.
Abstract: Battery/supercapacitor (SC) hybrid energy storage system (HESS) is an effective way to suppress the power fluctuation of photovoltaic (PV) power generation system during radiation change. This study focuses on the power sharing between different energy storage components with two optimisation objectives: energy loss and state of charge of SC. First, the topology of HESS and its connection with PV system are analysed. Second, the control targets of the HESS have been organised as optimisation objectives. A linear weighted summation algorithm based on variable weights is proposed to solve the multi-objective optimisation problem to obtain current reference of SC and battery. Third, the energy management system of the HESS is designed based on proposed algorithms. Simulation and experiment results verified the proposed algorithms and control strategy.
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TL;DR: In this article, the authors proposed a load flow analysis based on Taguchi's orthogonal arrays (OAA) to estimate the means and standard deviations of bus voltages, phase angles, line flows, and other metrics.
Abstract: Load flow studies are crucial in investigations of operation and planning problems in the power systems. Traditional methods for determining load flow are based on deterministic approaches. However, the parameters of a power system (such as load and renewable power generation) may be uncertain. An exact probabilistic load flow (PLF) study requires a long CPU time due to many convolution computations involving probability density functions. This paper proposes a novel PLF method that is based on Taguchi's orthogonal arrays. The proposed method utilises a few deterministic load flow solutions that are obtained using Taguchi's method to estimate the means and standard deviations of bus voltages, phase angles, line flows, and other metrics. A load flow calculation corresponds to an experiment in Taguchi's method. An optimal experiment is also specified by considering the largest deviation from the nominal load flow solution. A 25-bus standalone power system and a modified Institute of Electrical and Electronics Engineers (IEEE) 118-bus system are tested. The simulation results show that the proposed method not only requires fewer deterministic load flow solutions to perform PLF analysis than the traditional point-estimate method but also yields accurate means and standard deviations of bus voltages and line flows.
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TL;DR: In this paper, it is shown that the simultaneous use of the battery to locally increase self-sufficiency reduces the need for external power sources to correct the storage level, and the operational concept, the technical solutions, and a sensitivity analysis are presented.
Abstract: An increasing number of energy storages will be installed in buildings with photovoltaic systems. However, batteries with only local operation tasks do not exhaust their technical potential. Using the available battery capacity in terms of power and energy to provide ancillary system services is therefore economically reasonable. Providing primary control reserve power in combination with increasing local self-sufficiency has been identified as a promising option for decentralised PV battery systems. Thereby, part of the battery capacity is used to provide grid services and the remaining part for the management and optimisation of local system operation. Provision of self-sufficiency increase is limited, when the battery's state of charge is within certain limits. In this study, it is shown that the simultaneous use of the battery to locally increase self-sufficiency reduces the need for external power sources to correct the storage level. The operational concept, the technical solutions, and a sensitivity analysis are presented. Furthermore, billing and measuring issues as well as the current regulatory framework conditions in Germany are discussed.
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TL;DR: In this paper, an integrated small-signal model for a two-stage photovoltaic generation system is derived to investigate the system stability and sensitivity, taking into account the dynamics of the DC-link capacitor that was generally regarded as an ideal constant voltage source.
Abstract: Photovoltaic (PV) generation systems with two-stage topology are recently emerged due to its flexibility of installation. However, most studies on dynamic stability of the PV generation system are based either on the first DC/DC stage or the second DC/AC stage in previous literature. A system-level modelling and stability has not been reported significantly, which is a crucial issue for the design of the PV system controllers. In this study, an integrated small-signal model for a two-stage PV generation system is derived to investigate the system stability and sensitivity. The proposed model takes into account the dynamics of the DC-link capacitor that was generally regarded as an ideal constant voltage source in previous researches. A v
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feedback based DC-link voltage control scheme is presented to address the non-linear relationship between capacitor energy and its voltage and thus a high performance DC-link voltage regulation is achieved. Hardware-in-loop tests using real time digital simulator are presented to validate the feasibility of the proposed method.