| 1. |
- Ali, Muhammad Taha, et al.
(författare)
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Analysis and Mitigation of SSCI in DFIG Systems With Experimental Validation
- 2020
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Ingår i: IEEE transactions on energy conversion. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0885-8969 .- 1558-0059. ; 35:2, s. 714-723
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Tidskriftsartikel (refereegranskat)abstract
- Sub-synchronous oscillations (SSOs) in doubly-fed induction generator (DFIG)-based series compensated power systems are mainly caused by sub-synchronous control interaction (SSCI). SSCI is the most recently found type of sub-synchronous resonances. In this article, SSCI is elaborated and investigated by performing eigenvalue analysis on a mathematically modeled DFIG system. The occurrence of SSCI is observed and the results of eigenvalue analysis are validated through a down-scaled 7.5-kW experimental setup of a grid-connected DFIG. Based on the analysis, the proportional control parameters of the rotor-side converter (RSC) are found to be very sensitive towards the sub-synchronous modes of the system. The results obtained from both the simulation and the experimental analysis show that if the sensitive proportional parameters of the RSC are tuned properly, then the DFIG system can become immune to the SSCI for any level of series compensation.
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| 2. |
- Asef, Pedram, et al.
(författare)
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Multiobjective Design Optimization Using Dual-Level Response Surface Methodology and Booth's Algorithm for Permanent Magnet Synchronous Generators
- 2018
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Ingår i: IEEE transactions on energy conversion. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8969 .- 1558-0059. ; 33:2, s. 652-659
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies a dual-level response surface methodology (DRSM) coupled with Booth's algorithm using a simulated annealing (BA-SA) method as a multiobjective technique for parametric modeling and machine design optimization for the first time. The aim of the research is for power maximization and cost of manufacture minimization resulting in a highly optimized wind generator to improve small power generation performance. The DRSM is employed to determine the best set of design parameters for power maximization in a surface-mounted permanent magnet synchronous generator with an exterior-rotor topology. Additionally, the BA-SA method is investigated to minimize material cost while keeping the volume constant. DRSM by different design functions including mixed resolution robust design, full factorial design, central composite design, and box-behnken design are applied to optimize the power performance resulting in very small errors. An analysis of the variance via multilevel RSM plots is used to check the adequacy of fit in the design region and determines the parameter settings to manufacture a high-quality wind generator. The analytical and numerical calculations have been experimentally verified and have successfully validated the theoretical and multiobjective optimization design methods presented.
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| 3. |
- Astero, Poria, 1984-, et al.
(författare)
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Improving PV Dynamic Hosting Capacity Using Adaptive Controller for STATCOMs
- 2019
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Ingår i: IEEE transactions on energy conversion. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8969 .- 1558-0059. ; 34:1, s. 415-425
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Tidskriftsartikel (refereegranskat)abstract
- High penetrations of renewable energy sources (RES) in distribution grids lead to new challenges in voltage regulation. These challenges are not just limited to the steady-state voltage rise, but they are extended to rapid voltage changes due to wind speed variations and moving clouds, casting shadows on photovoltaic panels. According to EN50160 in low-voltage (LV) grids, the steady-state voltage should not exceed 1.1 pu (static characteristic), and rapid voltage changes should be kept less than 0.05 pu (dynamic characteristic). These two characteristics may limit the maximum amount of RES that can be installed in LV grids, called, respectively, the static hosting capacity (SHC) and dynamic hosting capacity (DHC). Although existing research just evaluated SHC in distribution grids, high-penetrated RES grids can be faced with such large voltage changes, which cause a smaller DHC than the SHC. This paper studies both SHC and DHC in distribution grids and proposes an adaptive controller for static synchronous compensators to regulate the steady-state and dynamic voltage while avoiding the unnecessary increase in the reactive power. The simulation results in some German distribution grids show considerable effects of the proposed adaptive controller on improving both SHC and DHC.
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| 4. |
- Bladh, Johan, et al.
(författare)
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Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements
- 2016
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Ingår i: IEEE transactions on energy conversion. - 0885-8969 .- 1558-0059. ; 31:1, s. 46-56
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Tidskriftsartikel (refereegranskat)abstract
- Standstill Frequency Response (SSFR) test data from a salient-pole synchronous machine with reconfigurable damper winding is presented. In addition to the regular measurements, the damper bar currents are measured and used to obtain the stator-to-damper transfer functions. The test is performed three times with physically different damper winding configurations. An extension to the standard SSFR test analysis scheme is suggested where the stator-to-damper transfer functions are included. The validity of the identified models is substantiated by comparison of the simulated and measured machine response to a drive torque step disturbance. It is found that the damper winding measurements can be incorporated in the analysis scheme to isolate the effect of the damper circuits. However, for a machine of the type studied, also the standard SSFR test produce yields models that are accurate enough for power system studies.
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| 5. |
- Bongiorno, Massimo, 1976, et al.
(författare)
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A Generic DFIG Model for Voltage Dip Ride-Through Analysis
- 2013
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Ingår i: IEEE Transactions on Energy Conversion. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-0059 .- 0885-8969. ; 28:1, s. 76-85
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Tidskriftsartikel (refereegranskat)abstract
- The modeling of a Doubly fed induction generator (DFIG) system for a wind turbine application is investigated in this paper. The electrical generating system is equipped with a dc crowbar system for fault ride through ability. After setting up the basic machine, converter, and grid-filter equations, the various controllers are derived and the selection of the regulator parameters is discussed. To validate the derived model, the investigated DFIG system is simulated using PSCAD/EMTDC and its dynamic response to voltage dips is compared to the dip behavior of an existing 2-MW wind turbine. It will be shown that the developed generic model exhibits the same dynamic performance as the actual wind turbine during and directly after a voltage dip recorded at the wind-turbine site, even in case of a severe event where the voltage at the connection point drops to 0% during the voltage dip.
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| 6. |
- Dahlborg, Elin, 1990-, et al.
(författare)
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Kaplan turbine model validation for large grid frequency disturbances
- 2021
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Ingår i: IEEE transactions on energy conversion. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8969 .- 1558-0059. ; 36:2, s. 611-618
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Tidskriftsartikel (refereegranskat)abstract
- The grid frequency stability is decreasing in many AC grids due to less inertia in these systems, and their stability is commonly evaluated through simulation. Hydropower often delivers frequency control, yet research on hydropower model validation for large grid frequency disturbances is scarce. We performed frequency control tests on a Kaplan unit and evaluated three models (called the standard grey-box, Kaplan grey-box, and white-box models) against validation data. The grey-box model parameters were identified with grey-box system identification, whereas the white-box model used index test data to relate guide vane opening and runner blade angle to net head, flow, and efficiency. All models accounted for steering mechanism backlash. The results showed that the white-box model was overall more reliable than the two grey-box models. However, all models had difficulties in simulating the output power the first few seconds after a large change in frequency. Moreover, backlash sizes had considerable performance impacts on all models. The uncertainties in hydropower model response during the first few seconds after a disturbance emphasize the importance of sufficient stability margins in grid frequency stability simulations.
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| 7. |
- Dong, Guangzhong, 1991, et al.
(författare)
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A Hierarchical Approach for Finite-time H- State Observer and Probabilistic Lifetime Prediction of Lithium-Ion Batteries
- 2021
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Ingår i: IEEE Transactions on Energy Conversion. - 1558-0059 .- 0885-8969. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Accurate state-of-charge (SOC) estimation and lifetime prognosis of lithium-ion batteries are of great significance for reliable operations of energy storage systems. This paper proposes a novel two-layer hierarchical approach for online SOC estimation and remaining-useful-life (RUL) prediction based on a robust observer and Gaussian-process-regression (GPR). At the bottom layer, an equivalent-circuit model is first developed to describe battery dynamics. Second, a combination method of a recursive least square method and a finite time H-1 observer is designed to estimate battery open-circuit-voltage (OCV) and SOC through stability and robustness analysis. Next, the estimated OCV and SOC are fed into the top layer to generate the incremental-capacity-analysis-based aging feature, through which a robust signature associated with battery aging is identified. The feature is further employed for RUL prediction based on GPR. The salient advantages of the proposed approach are that it can provide robust parameter estimation in a given finite-time interval, and the GPR-based RUL prediction can tackle longterm uncertainties in a principled Bayesian manner. Theoretical analysis and experimental results demonstrate the effectiveness of the proposed SOC observer and lifetime prediction methods.
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| 8. |
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| 9. |
- Eklund, Petter, 1989-, et al.
(författare)
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Experimental Evaluation of a Rare Earth-Free Permanent Magnet Generator
- 2021
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Ingår i: IEEE Transactions on Energy Conversion. - Piscataway : Institute of Electrical and Electronics Engineers (IEEE). - 1558-0059 .- 0885-8969. ; 36:1, s. 3-10
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Tidskriftsartikel (refereegranskat)abstract
- Low speed, high torque machines are used in wind turbines where the turbine rotor is directly connected to the generator. A permanent magnet synchronous generator using high-energy rare-earth permanent magnets (PMs) is one common choice for this application, but rare-earth PMs have supply insecurities and cost risks. A rare-earth free 32-pole PM generator, using ferrite PMs in a spoke-type rotor, for use in a 12 kW experimental wind turbine is built and tested. Voltages and currents at load and no load are measured, as well as the magnetic field in the end regions of the machine. The generator can deliver the required power at nominal speed and has low harmonic content in the output. The electrical measurements are compared to two-dimensional finite element design calculations and the experimental results are lower than expected from simulations. The measured voltage is lower than expected, requiring a higher current than calculated for the rated power. Three-dimensional magnetic field simulations show that there are leakage flux paths in the end-regions that the two-dimensional design calculations overlook, explaining the discrepancy between simulations and measurements.
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| 10. |
- Evestedt, Fredrik, et al.
(författare)
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Mitigation of Unbalanced Magnetic Pull in Synchronous Machines With Rotating Exciters
- 2021
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Ingår i: IEEE transactions on energy conversion. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8969 .- 1558-0059. ; 36:2, s. 812-819
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Tidskriftsartikel (refereegranskat)abstract
- A magnetization system with active compensation of unbalanced magnetic pull for synchronous machines with rotating exciters is demonstrated. The system used switched power electronics and a digital control system to control the currents in four rotor pole groups, each consisting of 3 poles. It was mounted on the shaft of a synchronous machine, providing an interface between a permanent magnet outer-pole brushless exciter and the segmented field winding. Measurements of magnetic flux density on each pole face and current control made it possible to control the airgap magnetic flux density to balance the machine magnetically, thus removing flux density space harmonics in the airgap and also the unbalanced magnetic pull. The construction of the system is presented along with results from experiments and simulations. Tests were performed with the stator winding both in series and with two parallel circuits. Approximately 80% reduction of static forces and 60% reduction of dynamic forces between the stator and rotor were observed when the system was running.
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