| 1. |
- Avila-Rojas, A. E., et al.
(author)
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Distribution network electric vehicle hosting capacity enhancement using an optimal power flow formulation
- 2022
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In: Electrical engineering (Berlin. Print). - : Springer. - 0948-7921 .- 1432-0487. ; 104:3, s. 1337-1348
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Journal article (peer-reviewed)abstract
- This paper presents a method based on an optimal power flow (OPF) procedure to determine the maximum Hosting Capacity (HC) of Electric Vehicles (EV) that can be supported by a distribution network. With a focus on the injection control of reactive power, it is possible to maximize the penetration of EV. The presented method is based on linearized power flow equations, allowing a significant reduction in the computational processing times. Two comparisons are presented. The first one is between a nonlinear and a linear OPF method. Second one, it is comparative analysis between legacy iterative (non-optimized) method of HC and the proposed method. The method is applied on the IEEE 13 node test feeder circuit showing its effectiveness and acceptable performance. Results demonstrate that the implemented method enhances the HC measured against a legacy HC method and decrease the computational time measures against nonlinear optimization methods.
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| 2. |
- Barg, Sobhi, 1984-, et al.
(author)
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Multi‑objective Pareto and GAs nonlinear optimization approach for fyback transformer
- 2019
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In: Electrical engineering (Berlin. Print). - Germany : Springer Berlin/Heidelberg. - 0948-7921 .- 1432-0487. ; 101:3, s. 995-1006
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Journal article (peer-reviewed)abstract
- Design and optimization of high-frequency inductive components is a complex task because of the huge number of variables to manipulate, the strong interdependence and the interaction between variables, the nonlinear variation of some design variables as well as the problem nonlinearity. This paper proposes a multi-objective design methodology of a 200-W flyback transformer in continuous conduction mode using genetic algorithms and Pareto optimality concept. The objective is to minimize loss, volume and cost of the transformer. Design variables such as the duty cycle, the winding configuration and the core shape, which have great effects on the former objectives but were neglected in previous works, are considered in this paper. The optimization is performed in discrete research space at different switching frequencies. In total, 24 magnetic materials, 6 core shapes and 2 winding configurations are considered in the database. Accurate volume and cost models are also developed to deal with the optimization in the discrete research space. The bi-objective (loss–volume) and tri-objective (loss–volume–cost) optimization results are presented, and the variations of the design variables are analyzed for the case of 60 kHz. An example of a design (30 kHz) is experimentally verified. The registered efficiency is 88% at full load.
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| 3. |
- Bouloumpasis, Ioannis, 1987, et al.
(author)
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Local flexibility market framework for grid support services to distribution networks
- 2022
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In: Electrical Engineering. - : Springer Science and Business Media LLC. - 1432-0487 .- 0948-7921. ; 104:2, s. 401-419
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Journal article (peer-reviewed)abstract
- The increasing volume of distributed resources and user-dependent loads in local networks has increased the concern for congestion and voltage management in distribution networks. To mitigate these issues, the implementation of local flexibility markets has been proposed to assist distribution system operators (DSOs) to manage their networks efficiently. This paper presents the framework of a local flexibility market, including the market participants and their roles. This framework aims to empower DSOs with a market-based instrument for the alleviation of congestion incidents by exploiting the flexibility of local resources. The proposed market aims to provide a tool for the holistic management of distribution networks by trading both reservation and activation of flexibility services, indifferent of the type and the timeline of the needed service. Three market modes are proposed, i.e., long-term, short-term and real-time market, and the interactions among those modes are shown. The operation of the market is explained in detail, including the identification of the needed services, the activation of the market as well as the proposed bidding, clearing and settlement mechanisms. The modelling of the long-term and real-time markets is also presented, along with some indicative simulation results for long-term and real-time services. Finally, the future developments as well as the major conclusions are discussed.
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| 4. |
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| 5. |
- Eriksson, Robert, et al.
(author)
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WAMS based identification for obtaining linear models to coordinate controllable devices
- 2012
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In: Electrical engineering (Berlin. Print). - : Springer Science and Business Media LLC. - 0948-7921 .- 1432-0487. ; 94:1, s. 27-36
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Journal article (peer-reviewed)abstract
- This paper is concerned with the use of subspace system identification techniques to derive a low-order black-box state-space model of a power system with many controllable devices. This is a multi-input multi-output open system model describing the power oscillatory behavior of the power system. The input signals are the controllable set points of the controllable devices, the output signals are the speed of some generators measured by a wide-area measurement system. This paper describes how to achieve and pre-process the data to use the subspace method to estimate and validate to finally assign an accurate model. This new approach can be used directly for the design of a centrally coordinated controller coordinating all the relevant controllable devices, with the aim to increase the damping of the modes in the system. Previously presented models, using input signals from controllable devices, use local measurements or output signals dependent on the actual operational point. The benefit of the presented method is that the used output signals are independent of the system state. This makes it possible to use a state-feedback controller, i.e., coordinated control. The presented method is applied in the Cigré Nordic 32-bus system including two high-voltage direct current (HVDC) links. The case study demonstrates that accurate low-order state-space models can be estimated and validated using the described method to accurately model the system's power oscillatory behavior.
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| 6. |
- Evestedt, Fredrik, et al.
(author)
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Controlling airgap magnetic flux density harmonics in synchronous machines using field current injection
- 2021
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In: Electrical engineering (Berlin. Print). - : Springer. - 0948-7921 .- 1432-0487. ; 103, s. 195-203
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Journal article (peer-reviewed)abstract
- In this paper, a method to control the harmonic content of the magnetic flux density in the airgap of a synchronous machine is presented. Voltage harmonics in one phase as well as the exciting magnetic forces can be affected. Switched power electronics were used to provide the field current to a synchronous machine, the control added specific current harmonics to the DC field current in order to minimize either voltage harmonics or magnetic forces. The method is verified and compared with simulations and experiments on an existing electrical machine.
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| 7. |
- Felicetti, Roberto, 1972-, et al.
(author)
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The influence of eddy currents on the excitation winding impedance of solid and laminated salient pole synchronous machines
- 2020
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In: Electrical engineering (Berlin. Print). - : Springer Science and Business Media LLC. - 0948-7921 .- 1432-0487. ; 102:4, s. 2553-2566
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Journal article (peer-reviewed)abstract
- This work investigates the establishment of steady-state eddy currents in solid and laminated salient poles and rotor rim of synchronous machines due to a periodic excitation voltage. It shows that the presence of eddy currents in the rotor magnetic circuit has the double effect of increasing the excitation winding AC-resistance and decreasing its magnetizing AC-inductance. According to that a simple analytical model is presented in here which allows a rapid rough estimation of the excitation winding AC-resistance when little information is available about the machine geometry and its electric/magnetic materials properties. The model is then verified by reproducing in frequency the excitation winding AC-resistance and the related power loss measured in two synchronous generators. Finally, the limits of reliability and applicability of the model are discussed. The model has implications for periodic field winding current control and voltage regulation in synchronous machines.
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| 8. |
- Mai, Tam T., et al.
(author)
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An overview of grid-edge control with the digital transformation
- 2021
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In: Electrical Engineering. - : Springer Science and Business Media LLC. - 1432-0487 .- 0948-7921. ; 103:4, s. 1989-2007
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Journal article (peer-reviewed)abstract
- Distribution networks are evolving to become more responsive with increasing integration of distributed energy resources (DERs) and digital transformation at the grid edges. This evolution imposes many challenges to the operation of the network, which then calls for new control and operation paradigms. Among others, a so-called grid-edge control is emerging to harmonise the coexistence of the grid control system and DER’s autonomous control. This paper provides a comprehensive overview of the grid-edge control with various control architectures, layers, and strategies. The challenges and opportunities for such an approach at the grid edge with the integration of DERs and digital transformation are summarised. The potential solutions to support the network operation by using the inherent controllability of DER and the availability of the digital transformation at the grid edges are discussed.
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| 9. |
- Norgren, Martin, et al.
(author)
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Depolarization dyadic for a cubic cavity : Illustrations and interpretation
- 2005
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In: Electrical engineering (Berlin. Print). - : Springer Science and Business Media LLC. - 0948-7921 .- 1432-0487. ; 87:5, s. 227-230
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Journal article (peer-reviewed)abstract
- The depolarization dyadic of the cubic cavity is examined for off-center positions inside the cavity. It is shown that at an edge two of the diagonal components have ill-defined limiting values and at a corner all three diagonal components are ill defined. Figures illustrating those peculiarities are presented. The explanation is found to be the non-unique limit of the solid angle subtended by an open surface when approaching a point on its rim.
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| 10. |
- Reinelt, Wolfgang
(author)
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Loop Shaping of Multivariable Systems with Hard Constraints on the Control Signal
- 2001
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In: Electrical engineering (Berlin. Print). - 0948-7921 .- 1432-0487. ; 83:4, s. 169-177
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Journal article (peer-reviewed)abstract
- A general framework for the design of multivariable control systems subject to hard constraints on each control channel is developed. The design procedure is based on the ℋ∞ loop shaping and relies on the calculation of the maximum possible control amplitude for a class of reference signals, bounded in amplitude and rate. Special attention is given to adjustment of the design weights in order to meet prescribed bounds on each control signal. A simulation example, the control of the vertical dynamics of an aircraft, illustrates the suggested procedure.
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