| 1. |
- Harnefors, Lennart, 1968, et al.
(författare)
-
Input-admittance calculation and shaping for controlled voltage-source converters
- 2007
-
Ingår i: IEEE Transactions on Industrial Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0278-0046 .- 1557-9948. ; 54:6, s. 3323-3334
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Tidskriftsartikel (refereegranskat)abstract
- A controlled power electronic converter can cause local instabilities when interacting with other dynamic subsystems in a power system. Oscillations at a certain frequency cannot, however, build up if the converter differential input admittance has a positive conductance (real part) at that frequency, since power is then dissipated. In this paper, input-admittance expressions for a voltage-source converter are derived. It is seen how the admittance can be shaped in order to get a positive real part in the desired frequency regions by adjusting the controller parameters.
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| 2. |
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| 3. |
- Härsjö, Joachim, 1987, et al.
(författare)
-
PERMANENT MAGNET SYNCHRONOUS GENERATOR INTER TURN FAULT IDENTIFICATION USING STATOR CURRENT ANALYSIS
- 2013
-
Ingår i: 9th PhD Seminar on Wind Energy in Europe, EAWE.
-
Konferensbidrag (refereegranskat)abstract
- A three phase permanent magnet synchronous generator is modeled both as a FEM model and an analytically model with an additional fourth winding that represents the faulty part of the machine. The faulty part is described as a fraction of the healthy machine. The proposed method can be used for multi pole machines as a general method for calculating the inductances is shown. Simulations show that the largest contributing parameter is the fault resistance, i.e. the contact resistance of the inter turn fault. FEM and analytical simulations show similar results but with amplitude an amplitude difference.
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| 4. |
- Wallmark, Oskar, et al.
(författare)
-
Input Admittance Expressions for Field-Oriented Controlled Salient PMSM Drives
- 2012
-
Ingår i: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107. ; 27:3, s. 1514-1520
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents analytical expressions for the converter input admittance in field-oriented controlled permanentmagnet synchronous motor (PMSM) drives. The effect of rotorsaliency is taken into consideration and the derived admittance expressions are valid for maximum-torque-per-ampere as well ashigh-speed (field weakening) operation. Experimental results illustrate the validity of the derived admittance expressions. The presented work can be used to predict dc-link voltage instabilities inPMSM drives in, e.g., railway traction, aerospace and automotive applications.
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| 5. |
- Abasian, Alireza, et al.
(författare)
-
Vacuum-Packaged Piezoelectric Energy Harvester for Powering Smart Grid Monitoring Devices
- 2019
-
Ingår i: IEEE Transactions on Industrial Electronics. - 0278-0046 .- 1557-9948. ; 66:6, s. 4447-4456
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents an analytical method for the design and power optimization of vacuum-packaged piezoelectric energy harvesters. It is shown that the maximum power point of a vacuum-packaged energy harvester is different from the conventional one which occurs when the electrical damping ratio equals to its mechanical counter-part. Also, it is shown that the captured power by a vacuum-packaged energy harvester is highly sensitive to the vibration frequency due to very low-mechanical damping ratio, e.g., up to 50% power drops corresponding to 2% deviations in the frequency. The analysis and design are performed in the context of an ac-line magnetic field energy harvester in which the line frequency is also fixed and this energy harvester is useful for developing the self-powered wireless monitoring devices. Furthermore, the vacuum-packaged devices are inherently robust against dust storm and icing phenomenon, which occur for overhead power lines. The proposed analytical method is established based on simplified assumptions and then an accurate method is developed for the analysis of vacuum-packaged devices. Obtained theoretical results are verified in the laboratory through a prototype of the vacuum-packaged piezoelectric device, which captures up to 90 mu W from a 10-A line current.
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| 6. |
- Alsulami, A., et al.
(författare)
-
Balancing asymmetrical load using a static var compensator
- 2015
-
Ingår i: IEEE PES Innovative Smart Grid Technologies Conference Europe. ; 2015-January:January
-
Konferensbidrag (refereegranskat)abstract
- Power electronic controllers are employed in the transmission and distribution levels of the power systems. In transmission level applications, Flexible AC Transmission System (FACTS) controllers, consist of shunt and series static compensators, are applied for power flow control, stability enhancement, voltage regulation and power oscillation damping. A Static Var Compensator (SVC) is a shunt-connected FACTS controller that is able to exchange reactive power with the power system in a controlled way. The SVC can be used for load balancing applications to reduce negative sequence components in the network to an acceptable level. The aim of the paper is to evaluate the dynamic performance of the SVC negative sequence controller. The benefits of the SVC negative sequence controller and characteristics is presented. The simulation illustrates that the SVC allows utilities to balance asymmetrical loads to mitigate the network negative sequence components.
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| 7. |
- Asimakopoulos, Panagiotis, 1985, et al.
(författare)
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Current Sharing inside a High Power IGBT Module at the Negative Temperature Coefficient Operating Region
- 2016
-
Ingår i: 18th European Conference on Power Electronics and Applications, EPE 2016 ECCE Europe, Karlsruhe, Germany, 5-9 September 2016. - 2325-0313. - 9789075815245
-
Konferensbidrag (refereegranskat)abstract
- This work investigates the current sharing effect of a high power Soft Punch Through IGBT module in the Negative Temperature Coefficient region. The unbalanced current sharing between two of the substrates is demonstrated for different current and temperature levels and its impact on the thermal stressing of the device is evaluated. The results indicate that the current asymmetry does not lead to a significant thermal stressing unbalance between the substrates.
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| 8. |
- Asimakopoulos, Panagiotis, 1985, et al.
(författare)
-
Design of a Modular Multilevel Converter as an Active Front-End for a magnet supply application
- 2014
-
Ingår i: 2014 16th European Conference on Power Electronics and Applications (EPE'14-ECCE Europe), Lappeenranta, Finland, 26-28 August 2014. - 2325-0313. - 9781479930159
-
Konferensbidrag (refereegranskat)abstract
- The aim of this work is to describe the general design procedure of a Modular Multilevel Converter (MMC) applied as an Active Front-End (AFE) for a magnet supply for beam accelerators. The dimensioning criteria for the converter and the dc-link capacitance are presented and the grid transformer requirements are set. Considering the converter design, the arm inductance calculation is based on the specifications for the arm-current ripple and the DC-link fault tolerance, but, also, on the limitation of the second harmonic and the second-order LC resonance of the arm current. The module capacitance value is evaluated by focusing on the required switching dynamics and the capacitor-voltage ripple according to a newly proposed graphical method. The loading of each semiconductor in the half bridge is calculated via simulation, indicating the unsymmetrical current distribution. It is concluded that the current distribution for each semiconductor depends on the mode of operation of the converter. The different criteria for the choice of the number of modules per arm are discussed. Finally, the complete system, including a model for the load and the converter control strategy applied to the converter is simulated and obtained results are presented.
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| 9. |
- Asimakopoulos, Panagiotis, 1985, et al.
(författare)
-
Heat sink design considerations in medium power electronic applications with long power cycles
- 2015
-
Ingår i: 17th European Conference on Power Electronics and Applications, EPE-ECCE Europe 2015, Geneva, Switzerland, 8-10 September. - 9789075815221
-
Konferensbidrag (refereegranskat)abstract
- The aim of this work is to investigate the impact of the heat sink thickness and material, as well as, of the convection coefficient of the water cooling system on the power-electronics module thermal stressing. The heat extraction capability of different thicknesses is tested. It is concluded that the thickest heat sink results in marginally lower temperature variation at the junction level compared to the second thickest one. In the thickest heat sink case, the linear dependence of the thermal resistance on the thickness counteracts the benefit of the increased thermal capacitance. The increase in the cooling medium flow rate, which corresponds to an increase in the convection coefficient between the heat sink bottom surface and the water, can be avoided by increasing the thickness of the heat sink. In this way, the energy consumption of the cooling system is reduced. The increase in the flow rate drastically reduces the thermal stressing in the thinnest heat sink case. The increase of the heat sink thickness can be beneficial for long power cycles. Copper and aluminum are the two materials that are compared, with the copper heat sink exhibiting a slightly increased performance. The study is conducted for a medium power DC-DC converter of a magnet supply with focus on long power cycles.
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| 10. |
- Asimakopoulos, Panagiotis, 1985, et al.
(författare)
-
IGBT Power Stack Integrity Assessment Method for High-Power Magnet Supplies
- 2019
-
Ingår i: IEEE Transactions on Power Electronics. - 0885-8993 .- 1941-0107. ; 34:11, s. 11228-11240
-
Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a method for assessing the integrity of a series of insulated-gate bipolar transistor (IGBT) power stacks during factory-acceptance tests and service stops. The key challenge that is addressed in this paper is detecting common assembly issues that affect the power stack thermal path as well as distinguishing the acute aging effects of bond-wire lift-off and solder delamination. The method combines offline Vce measurements with current in the extended Zero Temperature Coefficient (ZTC) operating region as well as with sensing current without modifications to the power stack. It also employs on-the-stack Vce calibration for both the measurements. Additionally, only a fixed duty cycle pattern is needed to control the switches. The paper also presents a sensitivity analysis of the method to various parameters such as the current level in the extended ZTC operating region, the precision of the Vce measurement, as well as the ambient, the cooling-water, and the junction temperatures. The experimental results are obtained from a high-current IGBT power stack used in a magnet power supply for particle accelerators and are compared favorably to results from finite element method and lumped parameter network simulations confirming the applicability of the method.
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| 11. |
- Asimakopoulos, Panagiotis, 1985, et al.
(författare)
-
On V-ce Method: In Situ Temperature Estimation and Aging Detection of High-Current IGBT Modules Used in Magnet Power Supplies for Particle Accelerators
- 2019
-
Ingår i: IEEE Transactions on Industrial Electronics. - 0278-0046 .- 1557-9948. ; 66:1, s. 551-560
-
Tidskriftsartikel (refereegranskat)abstract
- Magnet power supplies used in particle accelerators are a specialized application of power electronics that require long lifetime operation with no unscheduled interruptions and high output current precision. In this paper, the V-ce method with sensing current is considered for the estimation of the junction temperature and the aging detection of high-current insulated gate bipolar transistor (IGBT) modules used in this specialized application. First, sensitivity analysis of the sensing current and the gate-emitter voltage are documented to quantify their impact on the precision of the V-ce method for high-current modules independently of the application of interest. Two measuring circuits offering ease of calibration and reduced number of components are proposed but their applicability is not limited to this application. Their performance is tested on a 1.6 kA IGBT module that exhibits the highest current ratings documented for the V-ce method with sensing current. The test is carried out at a switching frequency of 6.5 kHz using an experimental set-up that emulates a phase leg of the considered power supply. The V-ce method with sensing current is evaluated for the aging detection of high-current IGBT modules in general and its effectiveness for the specialized application is verified experimentally.
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| 12. |
- Asimakopoulos, Panagiotis, 1985, et al.
(författare)
-
Thermal stressing mitigation possibility intended for a DC-current magnet supply based on high power IGBT modules
- 2017
-
Ingår i: 2017 19th European Conference on Power Electronics and Applications. - 2325-0313. - 9789075815276 ; 2017-January
-
Konferensbidrag (refereegranskat)abstract
- This work investigates the possibility to reduce the thermal stressing of high power IGBT modules in a DC-current application. Using four load current profiles as examples, two mitigation strategies are presented and their benefit to the power stack in terms of lifetime prolongation is evaluated. In the final part of the work, the investigation focuses on the relation between the shape of the load current and the potential for thermal stressing limitation that the proposed mitigation strategies can provide.
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| 13. |
- Bagheri, Azam, 1982, et al.
(författare)
-
Estimation of frequency-dependent impedances in power grids by deep lstm autoencoder and random forest
- 2021
-
Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 14:13
-
Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a deep-learning-based method for frequency-dependent grid impedance estimation. Through measurement of voltages and currents at a specific system bus, the estimate of the grid impedance was obtained by first extracting the sequences of the time-dependent features for the measured data using a long short-term memory autoencoder (LSTM-AE) followed by a random forest (RF) regression method to find the nonlinear map function between extracted features and the corresponding grid impedance for a wide range of frequencies. The method was trained via simulation by using time-series measurements (i.e., voltage and current) for different system parameters and verified through several case studies. The obtained results show that: (1) extracting the time-dependent features of the voltage/current data improves the performance of the RF regression method; (2) the RF regression method is robust and allows grid impedance estimation within 1.5 grid cycles; (3) the proposed method can effectively estimate the grid impedance both in steady state and in case of large transients like electrical faults.
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| 14. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
A Novel Capacitor-Voltage Balancing Strategy for Double-Y STATCOM Under Unbalanced Operations
- 2021
-
Ingår i: IEEE Transactions on Industry Applications. - 0093-9994 .- 1939-9367. ; 57:3, s. 2692-2701
-
Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a novel capacitor-voltage balancing strategy for the double-Y MMC STATCOM operated under unbalanced current conditions of the system. The proposed method, based on zero-sequence voltage injection, manipulates the current distribution between the converter arms to minimize the converter ratings. The proposed balancing strategy is compared with the classical approach, based on controlling the circulating dc currents. For the same unbalanced conditions, the proposed strategy leads to lower energy rating for the converter as compared with the classical one, while the semiconductor ratings remain the same in both strategies. Theoretical findings are verified through experimental results.
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| 15. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
A Proposed Capacitor Voltage-Balancing Strategy for Double-Y STATCOM Operated Under Unbalanced Conditions
- 2019
-
Ingår i: 2019 IEEE Energy Conversion Congress and Exposition, ECCE 2019.
-
Konferensbidrag (refereegranskat)abstract
- This paper proposes a novel capacitor voltage-balancing strategy for the double-Y MMC STATCOM operated under unbalanced conditions. The proposed method, based on zero-sequence voltage injection, manipulates the current distribution between the converter arms to minimize the converter ratings. The proposed balancing strategy is compared with the classical approach based on controlling the circulating dc currents. For the same unbalanced conditions, the proposed strategy leads to lower energy rating for the converter as compared with the classical one, while the semiconductor ratings remain the same in both strategies. Theoretical findings are verified through simulation results.
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| 16. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
An overview of multilevel converter topologies for grid connected applications
- 2013
-
Ingår i: 15th European Conference on Power Electronics and Applications (EPE). 2-6 Sept. 2013, Lille, France.. - 9781479901166 ; , s. 1-10 (Article no. 6634634)
-
Konferensbidrag (refereegranskat)abstract
- This paper provides an overview of multilevel converter topologies for grid connected applications. Different converter topologies such as Diode Clamp Converter (DCC), Capacitor Clamp Converter (CCC) and Chain Link Converter (CLC) are considered and compared from different aspects such as component sizing, complexity, efficiency and reliability. Thanks to its modular structure, the CLC appears as the most attractive topology for high power and high voltage applications. Single-Star Bridge-Cell (SSBC), Single-Delta Bridge-cell (SDBC), Double-Star Bridge-Cell (DSBC) and DoubleStar Chopper-Cell (DSCC) are four basic subset topologies of CLC. A comprehensive comparison of these subset topologies for the CLC is provided for the particular application of grid connected converters. The problem of operation under unbalance grid conditions and the ability of this converter topology to inject negative sequence into the grid are discussed. It will be shown that due to the lack of a common DC link between phases, this converter topology presents limited negative sequence injection capability when the phase legs are connected in delta, while in case of star connection voltage balancing between the different cells of the converter becomes problematic due to the uneven current distribution among phases. This represents the main limitation of this converter topology, especially when used for load balancing and active filter applications.
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| 17. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
DC-link voltage modulation for individual capacitor voltage balancing in cascaded H-bridge STATCOM at zero current mode
- 2018
-
Ingår i: 2018 20th European Conference on Power Electronics and Applications, EPE 2018 ECCE Europe. - 9789075815283
-
Konferensbidrag (refereegranskat)abstract
- Individual capacitor voltage balancing of cascaded H-Bridge converters is one of the challenges in the field of multilevel converters, especially when the converter is operating at zero-current mode. This is due to the fact that the balancing algorithm requires information about the power direction for proper insertion of the different cells of the converter. In case of delta configuration of the phase-legs of the converter, a circulating current inside the delta can be used for balancing purposes. However, this approach can not be used for the star configuration. Focusing on the star, this paper first highlights the issue related to the capacitor voltage balancing at zero-current mode and second proposes a novel method to overcome this problem. The proposed method is based on modulation of the DC-link voltages. The method provides a small amount of current flow during the zero-current mode operation. This current enables the sorting algorithm to provide an appropriate individual balancing. The proposed method is applied to a 7-level star connected cascaded H-Bridge STATCOM modeled in PSCAD and simulation results show the effectiveness of the proposed method in balancing the capacitors voltages when no current is exchanged with the grid. Finally the proposed method is experimentally verified through a down-scaled laboratory set-up.
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| 18. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
Impact of capacitor balancing strategies on converter ratings for star-connected cascaded H-bridge STATCOM
- 2017
-
Ingår i: 19th European IEEE Conference on Power Electronics and Applications (EPE'17 ECCE Europe). - 2325-0313. - 9789075815276
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a comparison between two DC-voltage balancing strategies for cascaded star-connected multilevel STATCOM: zero-sequence voltage, and negative-sequence current control. Different levels of unbalance and grid strengths are considered. The impact of the control strategies on the convert ratings in terms of voltage and current requirements are compared and the operating range of the converter using each control strategy is theoretically derived. The results show that for a given system ratings, the operating range of the converter using negative-sequence current control is wider than the zero-sequence voltage control when the STATCOM is connected to weak grids. On the contrary, in case of connection to strong grids the zero-sequence voltage control can provide wider operating range. PSCAD simulation results are provided to prove the theoretical results.
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| 19. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
Impact of frequency modulation ratio on capacitor cells balancing in phase-shifted PWM based chain-link STATCOM
- 2014
-
Ingår i: 2014 IEEE Energy Conversion Congress and Exposition, ECCE 2014. - 9781479956982 ; , s. 1931-1938
-
Konferensbidrag (refereegranskat)abstract
- The purpose of this paper is to investigate the impact of switching harmonics on the instantaneous power that flows in the cells of a chain-link based STATCOM when using Phase-Shifted PWM. Two different cases are investigated for the converter cells: low, and high switching frequency. It is shown that any deviation from the ideal conditions lead to undesired harmonics, which will impact the charge of the dc capacitors. It is also shown that for low switching frequencies, cells voltage sideband harmonics interact with baseband harmonics of the current and causes extra source of unbalance. In order to provide more uniform power distribution among the cells, two different methods called, a) carrier swapping and b) non-integer frequency modulation ratio are studied. In particular, it is shown that the selection of a non-integer frequency modulation ratio helps in providing a more uniform power distribution among cells of the same phase leg, thus contributing to the capacitors balancing. Theoretical conclusions are validated through PSCAD simulation results.
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| 20. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
Impact of Switching Harmonics on Capacitor Cells Balancing in Phase-Shifted PWM Based Cascaded H-Bridge STATCOM
- 2016
-
Ingår i: IEEE Transactions on Power Electronics. - 0885-8993 .- 1941-0107. ; 32:1, s. 815-824
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this paper is to investigate the impact of switching harmonics on the instantaneous power distribution in the cells of a cascaded H-Bridge based STATCOM when using Phase-Shifted PWM. The case of high and low switching frequency for the converter cells are investigated and the interaction between voltage and current harmonics is analyzed. It is shown that in both cases, this interaction results in an uneven power distribution among the cells in the same phase leg, leading to drifting of the dc-capacitor voltages and thereby the need for proper stabilization control loops. It is also shown that the selected frequency modulation ratio affects the active power distribution among the cells. In particular, the selection of a non-integer frequency modulation ratio helps in providing a more uniform power distribution among cells of the same phase leg, thus contributing to the capacitors balancing. A methodology for optimal selection of the frequency modulation ratio is given. Theoretical conclusions are validated through simulation and experimental results.
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| 21. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
Individual capacitor voltage balancing in H-bridge cascaded multilevel STATCOM at zero current operating mode
- 2015
-
Ingår i: 17th European Conference on Power Electronics and Applications, EPE-ECCE Europe 2015, Geneva, Switzerland, 8-10 September. - 9789075815238
-
Konferensbidrag (refereegranskat)abstract
- Individual capacitor voltage balancing is one of the challenges in the field of multilevel converters, especially when the phase legs of the converter are connected in star configuration. This issue can be even more problematic when the converter is operating close to zero average current operating mode. This paper first shows the issue related to the capacitor voltage balancing at zero average-current mode and second proposes a novel algorithm to overcome this problem. The method proposes a modulation technique for individual balancing in H-bridge cascaded multilevel converters operated at zero average-current mode. The proposed algorithm modifies the conventional sorting algorithm based on current ripple. The individual DC-link voltage control method is applied to a 19-level star-connected cascaded converter in PSCAD and simulation results verify the ability of the proposed method in maintaining the balancing of the capacitors voltages at zero current injection mode. Several practical limitation such as forward voltage drop over semiconductor elements, noise in measured data, delay in the digital controller, switching deadtime, and grid voltage harmonics are also considered in the model.
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| 22. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
Investigation of negative sequence injection capability in H-bridge multilevel STATCOM
- 2014
-
Ingår i: 2014 16th European Conference on Power Electronics and Applications, EPE-ECCE Europe 2014. - 9781479930159 ; , s. Art. no. 6910883-
-
Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to investigate the ability of star- and delta-connected H-bridge multilevel STATCOMs to exchange negative-sequence current with the grid. Zero-sequence injection is utilized for capacitor voltage balancing. It is shown that a singularity for these configurations exists, leading to limitations in the utilization of the compensator for asymmetry compensation purposes.
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| 23. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
Investigation of Negative-Sequence Injection Capability of Cascaded H-Bridge Converters in Star and Delta Configuration
- 2016
-
Ingår i: IEEE Transactions on Power Electronics. - 0885-8993 .- 1941-0107. ; 32:2, s. 1675-1683
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to investigate the ability of cascaded H-bridge STATCOMs in star and delta configuration to exchange negative-sequence current with the connecting grid. Zero-sequence voltage for the star and zero-sequence current for the delta configuration are utilized to guarantee DC-capacitor voltage balancing. A general solution for the required zerosequence voltage/current for any kind of unbalanced condition is provided. The obtained solutions show that a singularity for both configurations exists under specific conditions, leading to infinite zero-sequence requirement. In case of star configuration, this singularity occurs when the amplitude of the positiveand negative-sequence components of the current output of the converter are equal. Analogously, the singularity for the delta configuration occurs when the amplitude of the positive- and negative-sequence components of the voltage at the converter terminals are equal. This singularity impacts the ratings of the system and imposes a limitation in the utilization of the compensator for unbalance compensation purposes, both in industrial and utility applications. Experimental results are presented to validate the theoretical analysis.
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| 24. |
- Behrouzian, Ehsan, 1985, et al.
(författare)
-
Operating range extension of cascaded H-bridge star using hybrid converter topology for STATCOM under unbalanced conditions
- 2019
-
Ingår i: 2019 21st European Conference on Power Electronics and Applications, EPE 2019 ECCE Europe. ; September 2019
-
Konferensbidrag (refereegranskat)abstract
- A controller for a hybrid converter for STATCOM applications, based on a cascaded H-bridge star in series with a generic converter connected at the star point, is proposed. The controller utilizes the generic converter in an optimized way to maximize the operating range of the converter, with focus on unbalanced operating conditions. So for each operating condition, the generic converter reference voltage minimizes the voltage rating of the star part. Theoretical investigations of the hybrid converter using the proposed control approach show that the hybrid converter allows to effectively extend the operating range of the converter under unbalanced conditions of the system, given that the generic converter is large enough to circulate the needed active power between the converter phase legs. This indicates that, depending on the requirements from the operator in terms of negative-sequence injection capability, the hybrid converter can be a valuable solution to overcome the limitations of the CHB star.
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| 25. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
A fast estimation algorithm for low-frequency oscillations in power systems
- 2011
-
Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011). Birmingham, 30 August-1 September 2011. - 9781612841670 ; , s. 1 - 10
-
Konferensbidrag (refereegranskat)abstract
- This paper deals with the application of the Recursive Least Square (RLS) algorithm for estimation of low-frequency oscillations. A novel resetting method to improve the speed of response of the estimation will be described. The effectiveness of the proposed method will be proven through simulation as well as experimental verification.
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| 26. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
A Modified RLS Algorithm for Online Estimation of Low-Frequency Oscillations in Power Systems
- 2016
-
Ingår i: IEEE Transactions on Power Systems. - 0885-8950 .- 1558-0679. ; 31:3, s. 1703 - 1714
-
Tidskriftsartikel (refereegranskat)abstract
- A number of methods have been proposed and implemented to improve system damping against low-frequency electromechanical oscillations in the power system. Among these, flexible ac transmission systems (FACTS) can be used to provide power oscillation damping (POD) function to the power system. The design of the POD algorithms in these devices requires estimation of the power oscillation frequency components and this is mostly achieved through the use of various filter combinations. However, these filter-based solutions are characterized by low bandwidth to extract the required signal components accurately, and this limits the dynamic performance of the FACTS controllers. Moreover, the filters are designed for specific frequencies, and a change in the system would reduce the performance of the methods. Thus, there is a need for a better estimation algorithm with fast and selective estimation of the required signal that is robust against system parameter uncertainties. In this paper, this is achieved by the use of a recursive least square algorithm that uses variable forgetting factor and a frequency adaptation mechanism. The investigated method has fast estimation in transient conditions without compromising its selectivity in steady state. The effectiveness of the proposed method is proven through simulation as well as experimental verification.
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| 27. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
An Adaptive Power Oscillation Damping Controller by STATCOM With Energy Storage
- 2015
-
Ingår i: IEEE Transactions on Power Systems. - 0885-8950 .- 1558-0679. ; 30:1, s. 484-493
-
Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the design of an adaptive power oscillation damping (POD) controller for a static synchronous compensator (STATCOM) equipped with energy storage. This is achieved using a signal estimation technique based on a modified recursive least square (RLS) algorithm, which allows a fast, selective, and adaptive estimation of the low-frequency electromechanical oscillations from locally measured signals during power system disturbances. The proposed method is effective in increasing the damping of the system at the frequencies of interest, also in the case of system parameter uncertainties and at various connection points of the compensator. First, the analysis of the impact of active and reactive power injection into the power system will be carried out using a simple two-machine system model. A control strategy that optimizes active and reactive power injection at various connection points of the STATCOM will be derived using the simplified model. Small-signal analysis of the dynamic performance of the proposed control strategy will be carried out. The effectiveness of the proposed control method to provide power oscillation damping irrespective of the connection point of the device and in the presence of system parameter uncertainties will be verified through simulation and experimental results.
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| 28. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Analytical Derivation of the AC-Side Input Admittance of a Modular Multilevel Converter with Open- and Closed-Loop Control Strategies
- 2018
-
Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 33:1, s. 248-256
-
Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the derivation of the ac-side input admittance of a grid-connected modular multilevel converter (MMC) under both open- and closed-loop ac-side current control strategies. The contribution of the internal dynamics of the MMC on the input admittance depends on the type of ac-side controllers implemented. For this reason, the input admittance is first derived with the MMC operating in open-loop on the ac side. The results are then modified to include various acside controllers in order to analyze the impact of the internal dynamics of the MMC on the total input admittance. Based on the findings, recommendations are given on modeling the input admittance of the MMC. Finally, the derived analytical models are verified using a detailed switching model of the MMC in the frequency domain.
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| 29. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Application of Recursive Least Square (RLS) Algorithm with Variable Forgetting Factor for Frequency Components Estimation in a Generic Input Signal
- 2012
-
Ingår i: 4th Annual IEEE Energy Conversion Congress and Exposition, ECCE 2012, Raleigh, NC, USA, 15 - 20 September 2012. - 9781467308014 ; , s. 2164-2171
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Konferensbidrag (refereegranskat)abstract
- Signal estimation is important for protection, systemstudy and control purposes. This paper deals with the application of a Recursive Least Square (RLS) algorithm with variable forgetting factor for estimation of frequency components in a generic input signal. Application areas such as synchronization and control in three-phase and single-phase systems for various grid conditions as well as estimation of harmonic and subsynchronous components will be discussed. Simulation and experimental results will be used to evaluate the dynamic performance of the algorithm.
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| 30. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Application of Recursive Least Squares Algorithm With Variable Forgetting Factor for Frequency Component Estimation in a Generic Input Signal
- 2014
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Ingår i: IEEE Transactions on Industry Applications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0093-9994 .- 1939-9367. ; 50:2, s. 1168-1176
-
Tidskriftsartikel (refereegranskat)abstract
- Signal estimation is important for protection, system study, and control purposes. This paper deals with the application of a modified recursive least squares algorithm, based on a variable forgetting factor, for estimation of frequency components in a generic input signal. Application areas such as synchronization and control in three- and single-phase systems for various grid conditions as well as estimation of harmonic and subsynchronous components will be discussed. Advantages of the proposed method over the available techniques in terms of estimation speed, frequency selectivity, and noise rejection capability will be described. Finally, simulation and experimental results will be used to evaluate the dynamic performance of the proposed method.
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| 31. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Comparison of Two Control Approaches for Stability Enhancement Using STATCOM with Active Power Injection Capability
- 2015
-
Ingår i: 7th Annual IEEE Energy Conversion Congress and Exposition, ECCE 2015, Montreal, Canada, 20-24 September 2015. - 2329-3721. - 9781467371506 ; , s. 4721-4728
-
Konferensbidrag (refereegranskat)abstract
- The application of two control strategies for shunt-connected FACTS devices to enhance the transient stability of a power system will be discussed in this paper. The main focus will be on the use of active power in the FACTS device and therefore a STATCOM with active power injection capability will be considered. The first approach represents the classical cascade controller that consists of an inner vector-current controller and various outer-control loops. The alternative approach controls the converter in a similar fashion as a synchronous generator, where the mechanical behavior of the machine is emulated in the control structure using the active power injection capability of the device. Using various simulation and experimental tests,the two methods will be compared in terms of their advantages and disadvantages, and a recommendation will be made on the use of the methods for transient stability enhancement.
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| 32. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Identification of resonance interactions in offshore-wind farms connected to the main grid by MMC-based HVDC system
- 2019
-
Ingår i: International Journal of Electrical Power and Energy Systems. - : Elsevier BV. - 0142-0615. ; 111, s. 101-113
-
Tidskriftsartikel (refereegranskat)abstract
- The transient stability of an offshore-wind farm connected to the main ac grid by a high-voltage direct current (HVDC) system depends on the control settings of the converters, the grid resonances and the system’s operating conditions. This paper focuses n identifying possible sources of resonance interactions that could endanger the overall stability of this kind of system. For this purpose, the ac-side input admittance/impedance of a full-power converter (FPC) wind turbine and an MMC-based HVDC system are derived and frequency-domain stability analysis tools are used to assess the impact of system and control parameters on stability. The analytical findings are verified through time-domain simulations and recommendations to increase system stability are given accordingly.
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| 33. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Impact of control loops on the low-frequency passivity properties of grid-forming converters
- 2020
-
Ingår i: 2020 22nd European Conference on Power Electronics and Applications, EPE 2020 ECCE Europe. ; , s. P.1-P.10
-
Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to evaluate the low-frequency passivity properties of grid-forming converters. Through the analysis of the frequency-dependent input admittance of the converter, the impact of various control loops is investigated. A simplified analytical model that is valid in the low-frequency range is also derived in order to identify possible control modifications to enhance the passivity of the system.
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| 34. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Impact of Control Loops on the Passivity Properties of Grid-Forming Converters with Fault-Ride through Capability
- 2021
-
Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 14:19
-
Tidskriftsartikel (refereegranskat)abstract
- Due to the increasing integration of renewable energy sources (RES) and a corresponding reduction of conventional generating units, there is nowadays a demand from the power-electronic converters to provide grid-forming properties through proper control of the converter systems. This paper aims to evaluate the impact of various control loops in a grid-forming control strategy equipped with a fault-ride through capability on the passivity properties of the converter system. Through the analysis of the frequency-dependent input admittance of the converter, the main factors affecting the passivity properties are identified. A simplified analytical model is derived in order to propose possible control modifications to enhance the system’s passivity at various frequencies of interest and the findings are validated through detailed time-domain simulations and experimental tests.
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| 35. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Impact of converter control parameters on the high-frequency resonance stability of a wind-farm connected to an ac grid
- 2019
-
Ingår i: 2019 21st European Conference on Power Electronics and Applications, EPE 2019 ECCE Europe.
-
Konferensbidrag (refereegranskat)abstract
- The transient stability of a wind-farm connected to an ac grid depends on the control settings of the involved converters, the grid resonances and the system's operating conditions. This paper focuses on investigating the impact of converter control algorithms on possible high-frequency resonance interactions that could endanger the overall stability of these kinds of systems. Mainly, two control strategies namely the conventional cascade control structure, consisting of an inner current-control loop and various outer-loop controls, and the immediate voltage control structure, which does not include a current-control loop, are compared. The impact of control parameters for both methods will be investigated as well. For this purpose, the ac-side input admittance of a wind-turbine converter is derived for the two control strategies and passivity-based frequency-domain analysis is used to assess their impact on system stability. Finally, the analytical findings are verified through detailed time-domain simulations and recommendations to increase system stability are given accordingly.
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| 36. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Impact of converter control strategy on low- and high-frequency resonance interactions in power-electronic dominated systems
- 2020
-
Ingår i: International Journal of Electrical Power and Energy Systems. - : Elsevier BV. - 0142-0615. ; 120
-
Tidskriftsartikel (refereegranskat)abstract
- The transient stability of power-electronic dominated systems such as wind farms and photo-voltaic power plants depends on the control settings of the involved converters, the grid resonances and the system’s operating conditions. This paper focuses on investigating the impact of converter control algorithms on possible interactions that could endanger the overall stability of these kinds of systems. Mainly, two control approaches namely the conventional cascaded control structure, consisting of an inner current-control loop and various outer-loop controls, and the immediate voltage control structure which generates the converter voltage directly from the power and voltage controllers without necessarily including a current-control loop, are compared. The latter control structure falls in the class of grid-forming control strategies and the impact of different variants of this control structure will also be investigated. For this purpose, the ac-side input admittance of a grid-connected converter is derived for the two approaches and passivity-based frequency-domain stability analysis is used to assess their impact on system stability. Finally, the analytical findings are verified through time-domain simulations and recommendations to increase system stability are given accordingly.
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| 37. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Impact of different static load characteristics on power oscillation damping by shunt-connected FACTS devices
- 2013
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Ingår i: Power Electronics and Applications (EPE), 2013 15th European Conference. - 9781479901166 ; , s. 1 - 10
-
Konferensbidrag (refereegranskat)abstract
- Loads constitute a major part of the power system and their characteristics greatly influence the stable operation of the system. One of the problems that are encountered in the power system is low-frequency electromechanical oscillations following disturbances. This paper deals with analysis of the impact of different static load characteristics on the performance of Power Oscillation Damping (POD) controllers by shunt-connected FACTS devices. From the results of the analysis, a modification to the POD controller will be proposed to deal with the impact of the load characteristics and its performance will be validated through small signal analysis and time domain simulation.
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| 38. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Improved Discrete Current Controller for Grid-connected Voltage Source Converters in Distorted Grids
- 2012
-
Ingår i: 4th Annual IEEE Energy Conversion Congress and Exposition, ECCE 2012, Raleigh, NC, USA, 15 - 20 September 2012. - 9781467308014 ; , s. 77-84
-
Konferensbidrag (refereegranskat)abstract
- This paper deals with improvements to the classicalProportional-Integral (PI) current controller for VoltageSource Converter (VSC) connected to a grid in the presenceof harmonics. A discrete PI current controller implemented in the synchronous reference-frame has simple design procedure and robust performance in ideal grid conditions. However, low order harmonics in the connecting grid will result in a steady state harmonic current flow between the converter and the grid. A method based on harmonic estimation to avoid the steady state harmonic injection to the grid will be discussed. The effectiveness of the described control method will be validated through simulation and experimental verification.
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| 39. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Independent damping control of multimode low-frequency oscillations using shunt-connected FACTS devices in power system
- 2014
-
Ingår i: 2014 IEEE Energy Conversion Congress and Exposition, ECCE 2014. - 9781479956982 ; , s. 716-723
-
Konferensbidrag (refereegranskat)abstract
- One of the problems encountered in a power system and that impacts its stable operation is low-frequency electromechanical oscillations. Depending on the system configuration, its operating conditions and the nature of the disturbance, one or more oscillation modes can be excited in the system. This paper deals with the design and analysis of an independent damping controller for multiple oscillation modes using shunt-connected FACTS devices. This is achieved using a selective and adaptive estimation of the various oscillation modes from locally measured signals. The effectiveness of the proposed control method to provide independent damping for the various oscillation modes in the presence of system parameter uncertainties will be verified through small-signal analysis and simulation using both single and multiple compensators.
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| 40. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
On the risk for subsynchronous control interaction in Type 4 based wind farms
- 2019
-
Ingår i: IEEE Transactions on Sustainable Energy. - 1949-3029 .- 1949-3037. ; 10:3, s. 1410-1418
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to investigate the risk for subsynchronous control interaction (SSCI) in Type 4 based wind farms connected to series-compensated transmission lines. For this purpose, the frequency-dependent input admittance of the turbine is derived and the power-dissipation properties of the turbine are used to identify those control parameters and operating conditions that mainly impact the behavior of the wind turbine in the subsynchronous frequency range. It is shown that the Type 4 wind turbine presents a non-dissipative behavior in the subsynchronous frequency range, which is mainly dependent on the speed of response of the synchronization loop, the reactive power controller and the active-power output. For a radial connection, a high series-compensation level also negatively impacts the risk for SSCI. The generalized Nyquist criterion is used to assess the stability of the system and the theoretical findings are verified using detailed time-domain simulations.
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| 41. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Passivity characterization of grid-forming converters with fault-ride through capability
- 2021
-
Ingår i: 2021 23rd European Conference on Power Electronics and Applications, EPE 2021 ECCE Europe.
-
Konferensbidrag (refereegranskat)abstract
- Due to the increase in the use of renewable energy sources (RES) and a corresponding reduction in the conventional energy generation systems, there is nowadays a demand from the power-electronic converters to provide grid-forming properties through proper control of the converter systems. This paper aims at evaluating the impact of various control loops of a grid-forming control strategy equipped with a fault-ride through capability on the passivity properties of the converter system. Through the analysis of the frequency-dependent input admittance of the converter, the main factors affecting the passivity property are identified. A simplified analytical model has been derived in order to propose possible control modifications to enhance system’s passivity at various frequencies of interest and the findings are verified through detailed time-domain simulations and experiments.
|
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| 42. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Power oscillation damping controller by static synchronous compensator with energy storage
- 2011
-
Ingår i: Energy Conversion Congress and Exposition (ECCE), 2011 IEEE. - 9781457705427 ; , s. 2977 - 2984
-
Konferensbidrag (refereegranskat)abstract
- This paper deals with a control strategy for power oscillation damping using Static Synchronous Compensator (STATCOM) with energy storage. First, analysis of power oscillation damping by only active and reactive power injection into the power system will be carried out using a single machine infinite bus and two machines system model. A control strategy that optimizes the use of active and reactive power injection for power oscillation damping based on locally measured signals will be derived. Small signal analysis of the dynamic performance of the proposed control strategy will be made. The effectiveness of the proposed control method to provide power oscillation damping irrespective of the connection point of the device will be verified by simulation.
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| 43. |
- Beza, Mebtu Bihonegn, 1981, et al.
(författare)
-
Stability of grid-connected modular multilevel converter with open- and closed-loop ac-side control
- 2017
-
Ingår i: 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe). - 2325-0313. - 9789075815276
-
Konferensbidrag (refereegranskat)abstract
- The stability of grid-connected modular multilevel converter (MMC) under two control strategies isstudied in this paper. For this purpose, the ac-side input admittance of the MMC is derived under openandclosed-loop ac-side control strategies. The derived analytical models are used to investigate theimpact of the two approaches on the stability of the MMC and detailed time-domain simulations areused to the verify the theoretical findings.
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| 44. |
- Bongiorno, Massimo, 1976, et al.
(författare)
-
A Generic DFIG Model for Voltage Dip Ride-Through Analysis
- 2013
-
Ingår i: IEEE Transactions on Energy Conversion. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-0059 .- 0885-8969. ; 28:1, s. 76-85
-
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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| 45. |
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| 46. |
- Bongiorno, Massimo, 1976, et al.
(författare)
-
Adaptive Generalized Delayed Signal Cancellation Method for Phase-Sequence Estimation
- 2017
-
Ingår i: 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe). - 2325-0313. - 9789075815276
-
Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to investigate the implementation of an adaptive generalized delayed signal cancellation (DSC) method for estimation of phase-sequence components. The proposed approach overcomes the intrinsic problems of the digital implementation of the classical DSC algorithm due to non-ideal selection of the sampling frequency and variations in the nominal system frequency. The derived algorithm is extended for estimation of harmonic components in the measured signal. The effectiveness of the proposed estimation method is validated through experimental results.
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| 47. |
- Bongiorno, Massimo, 1976, et al.
(författare)
-
An advanced cascade controller for series-connected VSC for voltage dip mitigation
- 2005
-
Ingår i: IEEE Industrial Application Society (IAS). ; 2, s. 873-880
-
Konferensbidrag (refereegranskat)abstract
- Power electronics converters connected in series with the grid can provide protection of sensitive processes against voltage dips. In this paper, an advanced cascade controller for series-connected voltage source converter (VSC), constituted by an outer voltage loop and an inner current loop, is presented. Positive and negative sequence components of voltage and current are controlled separately to achieve perfect compensation of unbalanced dips. Limitation of the VSC output voltage and compensation of the computational time delay are included in the current controller for both sequence components. Experimental results for the series-connected VSC with the proposed cascade controller under balanced and unbalanced voltage dips are presented.
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| 48. |
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| 49. |
- Bongiorno, Massimo, 1976
(författare)
-
Control of Voltage Source Converters for Voltage Dip Mitigation in Shunt and Series Configurations
- 2004
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Custom Power is the application of power electronics to improve the quality of power distribution for sensitive industrial plants. Industries reporting production stops due to voltage disturbances, like short interruptions and voltage dips, include paper mills, semiconductors facilities and other industries with fully automated production. Voltage dips are sudden drops in voltage, with duration between half a cycle and some seconds, mostly caused by clearing of short-circuit faults in the power system. Power electronic converters connected in shunt or series with the grid and equipped with energy storage can provide protection of sensitive processes against voltage dips. This thesis focuses on the control of Voltage Source Converter (VSC) connected in series or in shunt with the grid for mitigation of voltage dips. In both configurations, the core of the controller is the current controller. Since most voltage dips are unbalanced and have short duration, decisive factors for successful compensation are high speed of response and capability of handling unbalances. Three different algorithms for current control of VSC under unbalanced voltage conditions are presented and analyzed in detail. These algorithms include time delay compensation and reference voltage limitation with feedback, to improve the current control during overmodulation. Stability analysis of all three controllers is carried out. Different methods for sequence component detection are presented and compared, based on their transient performance. Simulations and experimental results on a 69-kVA prototype are presented and discussed for all three controllers. For use in a series-connected VSC, the three current controllers are completed with an outer voltage loop, thus realizing three cascade controllers that are presented and analyzed in detail. For all three controllers, stability analysis and simulation results with balanced and unbalanced voltage dips are also presented. The three controllers have been tested on a prototype series compensator and experimental results are presented in this thesis. Design and testing of the protection system for the series-connected VSC is also described in detail. Experimental results with non-linear load (diode rectifier) are shown. Finally, a similar cascade controller for voltage dip compensation with shunt-connected VSC is presented and tested via simulations. To improve the performance, a modified configuration including an LCL-filter between the VSC and the grid is proposed. It is also shown that by adding an active damping term in the inner current controller, undesired resonances between the filter components can be overcome and satisfactory mitigation of voltage dips can be achieved. A drawback is the high amount of injected current required if the grid is strong at the point of connection of the VSC.
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| 50. |
- Bongiorno, Massimo, 1976, et al.
(författare)
-
Cost-Effective Power Quality Improvement for Industrial Plant
- 2003
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Ingår i: IEEE Bologna PowerTech 2003. ; 4
-
Konferensbidrag (refereegranskat)abstract
- Disturbances in the voltage supply, especially voltage dips and short interruptions, can cause tripping of sensitive electronic equipment and cause production stops in many industries. This paper proposes a power-electronics based device, obtained by a combination of a Static Transfer Switch (STS) in series with a Static Series Compensator (SSC) for protection of large industrial distribution systems against voltage dips and short interruptions in a cost-effective way. The hybrid compensator is modeled and simulated with different types of dips using the simulation tool PSCAD/EMTDC. Design of the device and control strategies are discussed. An economic evaluation of the device is carried out.
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