| 1. |
- Abolpour, Roozbeh, et al.
(författare)
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Optimal frequency regulation in an uncertain islanded microgrid : A modified direct search algorithm
- 2022
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1416 .- 1752-1424. ; 16:4, s. 726-739
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a methodology for frequency regulation in a microgrid involving renewable energy sources (RES) using a dynamic controller, which is an output feedback controller (OFC). The parameters of OFC are tuned by searching the design space of the controller. Since the RES model is not exactly known, the uncertain model is derived and the OFC is considered for it. The goal of controller tuning is to find appropriate parameters of the controller such that the norm of frequency deviations, even in presence of uncertainties in the RES parameters is minimized. An algorithm based on searching the controller design space is suggested to find the suitable controller gains. The algorithm assumes the controller parameters lie in a convex space and searches the space systematically such that an appropriate solution is found. The method is proved mathematically and two theorems are mentioned, accordingly. Finally, a simulated model of a RES is utilized for algorithm evaluation and the results demonstrate the algorithm capability in optimal frequency regulation.
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| 2. |
- Bakhtiari, Hamed, et al.
(författare)
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Multi-criteria optimal sizing of hybrid renewable energy systems including wind, photovoltaic, battery, and hydrogen storage with ɛ-constraint method
- 2018
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1416 .- 1752-1424. ; 12, s. 883-892
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid renewable energy systems (HRES) should be designed appropriately with an adequate combination of different renewable sources and various energy storage methods to overcome the problem of intermittency of renewable energy resources. A multi-criteria approach is proposed in this study to design an HRES including wind turbine, photovoltaic panels, fuel cell, electrolyser, hydrogen tank, and battery storage unit with an intermittent load. Three design criteria including loss of power supply probability, total energy loss (TEL), and the power difference between generation and storing capacity (as TELSUB) are taken into account in minimising the total cost of the system considering the interest rate and lifetime. The justifications and advantages of using these criteria are thoroughly discussed along with appropriate presentation of the results. The purpose of considering TEL and TELSUB is discussed thoroughly. The ɛ-constraint method is used to handle practical constraints of the proposed multi-criteria problem to construct a multi-objective fitness function. Shuffled frog leaping algorithm is implemented to achieve better optimal results. The proposed approach is implemented using real wind speed and solar irradiance data for a specific location with an intermittent load demand. The results verify performance of the proposed multi-criteria design procedure.
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| 3. |
- Baudoin, Antoine, et al.
(författare)
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Thermal modelling of a passively cooled inverter for wave power
- 2015
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1416 .- 1752-1424. ; 9:4, s. 389-395
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Tidskriftsartikel (refereegranskat)abstract
- Owing to very costly maintenance operations, the reliability of electrical systems for offshore renewable energy is a major issue to make electricity production economical. Therefore proper thermal management is essential in order to avoid the components from being damaged by excessive temperature increase. Both analytic and computational fluid dynamics (CFD) models were implemented to assess the temperature increase in the inverter installed in a submerged substation and during working conditions. It was shown that this inverter could transmit a total power of up to about 35 kW. This limit is dependent on a certain distance between the modules and a perfect thermal contact with the hull. The influence of several of such parameters as well as the efficiency of passive cooling were studied.
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| 4. |
- Boström, Cecilia, et al.
(författare)
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Operation analysis of a wave energy converter under different load conditions
- 2011
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1416 .- 1752-1424. ; 5:3, s. 245-250
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Tidskriftsartikel (refereegranskat)abstract
- This study analyses the electrical behaviour of a direct-driven linear generator under different load conditions. The studied generator is used in a wave energy converter (WEC) that converts the energy in ocean waves into electric energy. To enable a grid connection of a WEC, the voltage must be converted, and thereby, the generator will be subjected to a non-linear damping. Depending on how the conversion system is designed, the damping will be different. In the case studied, the voltage is first rectified, and on the dc-side of the rectifier the voltage is kept constant by controlling the power through a converter. In order to study the electrical behaviour of the generator in this operation mode, a simulation model was made in MATLAB Simulink. The model of the generator was verified with experimental data from an offshore operating WEC. The result of the study shows that the model of the generator agrees with the real generator and can be used for analysing the electrical behaviour of the WEC. Moreover, the results show that the operation with a non-linear load will be different compared to a linear load case.
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| 5. |
- Ekinci, Serdar, et al.
(författare)
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Comparative analysis of the hybrid gazelle-Nelder-Mead algorithm for parameter extraction and optimization of solar photovoltaic systems
- 2024
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Ingår i: IET Renewable Power Generation. - : INST ENGINEERING TECHNOLOGY-IET. - 1752-1416 .- 1752-1424.
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Tidskriftsartikel (refereegranskat)abstract
- The pressing need for sustainable energy solutions has driven significant research in optimizing solar photovoltaic (PV) systems which is crucial for maximizing energy conversion efficiency. Here, a novel hybrid gazelle-Nelder-Mead (GOANM) algorithm is proposed and evaluated. The GOANM algorithm synergistically integrates the gazelle optimization algorithm (GOA) with the Nelder-Mead (NM) algorithm, offering an efficient and powerful approach for parameter extraction in solar PV models. This investigation involves a thorough assessment of the algorithm's performance across diverse benchmark functions, including unimodal, multimodal, fixed-dimensional multimodal, and CEC2020 benchmark functions. Notably, the GOANM consistently outperforms other optimization approaches, demonstrating enhanced convergence speed, accuracy, and reliability. Furthermore, the application of the GOANM is extended to the parameter extraction of the single diode and double diode models of RTC France solar cell and PV model of Photowatt-PWP201 PV module. The experimental results consistently demonstrate that the GOANM outperforms other optimization approaches in terms of accurate parameter estimation, low root mean square values, fast convergence, and alignment with experimental data. These results emphasize its role in achieving superior performance and efficiency in renewable energy systems. This study compares a new hybrid Gazelle-Nelder-Mead (GOANM) algorithm for parameter extraction in solar cells, evaluating single diode (SDM) and double diode (DDM) models. GOANM's performance is first tested on CEC2020 and classical benchmark functions. Then, it optimizes SDM and DDM for the RTC France solar cell and Photowatt-PWP201 PV module. Results demonstrate the algorithm's superior performance. image
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| 6. |
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| 7. |
- Elkington, Katherine, et al.
(författare)
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Nonlinear Power Oscillation Damping Controllers for Doubly Fed Induction Generators in Wind Farms
- 2013
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology. - 1752-1416 .- 1752-1424. ; 7:2, s. 172-179
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Tidskriftsartikel (refereegranskat)abstract
- This study presents two methods for designing power oscillation damping (POD) controllers for wind farms comprising doubly fed induction generators (DFIGs). The first is the residue method, which uses linear feedback. The second method uses a non-linear signal as feedback. Here linear matrix inequalities (LMIs) and regional pole placement are used to determine the feedback gains for multiple wind farms simultaneously so that the power system satisfies a minimum damping ratio. The impact of the designed POD controllers in wind farms is demonstrated in a test power system. Modal analysis is used to design controllers using both the residue and LMI methods, and dynamic simulations are used to demonstrate the contribution of the wind farms to power system damping. Numerical simulations show that DFIGs, such as those found in wind farms, are capable of damping oscillations, and also illustrate the effectiveness of using non-linear feedback controllers.
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| 8. |
- Fischer, Katharina, 1979, et al.
(författare)
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Thermo-mechanical stress in tubular solid oxide fuel cells: Part I - transient operating behaviour and the relevance of material creep
- 2012
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1424 .- 1752-1416. ; 6:3, s. 177-193
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Tidskriftsartikel (refereegranskat)abstract
- A spatially discretised thermo-electrochemical model is developed to calculate the temperature distribution in a tubular solid oxide fuel cell (SOFC). Model validation is accomplished based on the operating data from a demonstration plant. Using a mechanical model of the ceramic membrane-electrode assembly, the distribution of thermo-mechanical stress is calculated from the temperature profile. The resulting risk of fracture failure, being one of the crucial life-limiting factors of SOFC, is determined by means of Weibull analysis. The methodology and results are presented in two parts: Part I covers the dynamic operating properties of the SOFC and the time scale of material creep in its ceramic components. Part II deals with the risk of fracture failure related to transient operating scenarios, discusses its dependency on the operating conditions and derives a low-risk operating strategy. The dynamic operating behaviour is found to be dominated by the large thermal inertia of the solid cell components. An analysis of the creep relaxation indicates a significant relief of mechanical stress in the electrodes within a few hours of operation. This justifies a novel assumption regarding the stress-free state in the mechanical analysis of the fuel cell, which significantly increases the plausibility of the resulting risk of fracture failure.
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| 9. |
- Fischer, Katharina, 1979, et al.
(författare)
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Thermo-mechanical stress in tubular solid oxide fuel cells: Part II - Operating strategy for reduced probability of fracture failure
- 2012
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Ingår i: IET Renewable Power Generation. - : Institution of Engineering and Technology (IET). - 1752-1424 .- 1752-1416. ; 6:3, s. 194-205
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Tidskriftsartikel (refereegranskat)abstract
- A spatially discretised thermo-electrochemical model is developed to calculate the temperature distribution in a tubular solid oxide fuel cell (SOFC). This is used in a mechanical model to compute the distribution of thermo-mechanical stress in the ceramic membrane-electrode assembly of the cell. The resulting risk of fracture failure is determined by means of Weibull analysis. Part I of this work covers the dynamic operating properties of the SOFC and the time scale of material creep in its ceramic components. This work, Part II, deals with the risk of fracture failure related to transient operating scenarios, discusses its dependency on the operating conditions and derives a low-risk operating strategy. Contrary to the common perception, thermal gradients are found to have little impact on thermo-mechanical stress in the studied SOFC. Failure-relevant stress levels arise merely due to thermal mismatch of the ceramic layers. Regarding the operating strategy, the dynamics of changes in operating conditions are of minor importance for the resulting risk of failure, while operating strategies aiming at a constant mean cell temperature prove to be advantageous. The consideration of material creep is shown to be essential for a sound analysis of thermo-mechanical stress and risk of fracture in the investigated SOFC.
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| 10. |
- Fu, Hao, et al.
(författare)
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Asynchronous multi-rate method of real-time simulation for active distribution networks
- 2023
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Ingår i: IET Renewable Power Generation. - : INST ENGINEERING TECHNOLOGY-IET. - 1752-1416 .- 1752-1424.
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Tidskriftsartikel (refereegranskat)abstract
- The real-time simulation of active distribution networks (ADNs) can provide an accurate insight into transient behaviours, but faces challenges in simulation efficiency and flexibility brought by larger system scales and wider time-scale ranges. This paper presents an asynchronous multi-rate (AMR) method and design for the real-time simulation of large-scale ADNs. In the proposed method, the entire ADN was decoupled into different subsystems according to accuracy requirements, and optimized time-steps were allocated to each subsystem to realize a fully distributed simulation. This not only alleviated the time-step coordination problem existing in multi-rate real-time simulations, but also enhanced the flexible expansion capabilities of the real-time simulator. To realize the AMR real-time simulation, a multi-rate interfacing method, synchronization mechanism, and data communication strategy are proposed in this paper, and their hardware design is also presented in detail. A modified IEEE 123-node system with photovoltaics and wind turbine generators was simulated on a 3 field-programmable gate arrays (FPGAs)-based AMR real-time simulator. The real-time results were captured by the oscilloscope and verified with PSCAD/EMTDC, which demonstrated the superiority in simulation flexibility and accuracy compared with the synchronous multi-rate (SMR) method.
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