| 1. |
- Ahmed, Noman, et al.
(author)
-
A computationally efficient continuous model for the modular multilevel converter
- 2014
-
In: IEEE Journal of Emerging and Selected Topics in Power Electronics. - : IEEE. - 2168-6777. ; 2:4, s. 1139-1148
-
Journal article (peer-reviewed)abstract
- Simulation models of the modular multilevel converter (MMC) play a very important role for studying the dynamic performance. Detailed modeling of the MMC in electromagnetic transient simulation programs is cumbersome, as it requires high computational effort and simulation time. Several averaged or continuous models proposed in the literature lack the capability to describe the blocked state. This paper presents a continuous model, which is capable of accurately simulating the blocked state. This feature is very important for accurate simulation of faults. The model is generally applicable, although it is particularly useful in high-voltage dc applications.
|
|
| 2. |
|
|
| 3. |
- Ahmed, Noman, et al.
(author)
-
Efficient Modeling of an MMC-Based Multiterminal DC System Employing Hybrid HVDC Breakers
- 2015
-
In: IEEE Transactions on Power Delivery. - : IEEE. - 0885-8977 .- 1937-4208. ; 30:4, s. 1792-1801
-
Journal article (peer-reviewed)abstract
- The feasibility of future multiterminal dc (MTDC) systems depends largely on the capability to withstand dc-side faults. Simulation models of MTDC systems play a very important role in investigating these faults. For such studies, the test system needs to be accurate and computationally efficient. This paper proposes a detailed equivalent model of the modular multilevel converter (MMC), which is used to develop the MTDC test system. The proposed model is capable of representing the blocked-mode operation of the MMC, and can be used to study the balancing control of the capacitor voltages. In addition, the operation of the MMC when redundant submodules are included in the arms can also be studied. A simplified model of a hybrid high-voltage dc breaker is also developed. Hence, the developed test system is capable of accurately describing the behavior of the MMC-based MTDC system employing hybrid HVDC breakers, during fault conditions. Using time-domain simulations, permanent dc-side faults are studied in the MTDC system. In addition, a scheme to control the fault current through the MMC using thyristors on the ac side of the converter is proposed.
|
|
| 4. |
- Ahmed, Noman, et al.
(author)
-
Performance of the modular multilevel converter with redundant submodules
- 2015
-
In: IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781479917624 ; , s. 3922-3927
-
Conference paper (peer-reviewed)abstract
- The modular multilevel converter (MMC) is the state-of-the-art voltage-source converter (VSC) topology used for various power-conversion applications. In the MMC, submodule failures can occur due to various reasons. Therefore, additional submodules called the redundant submodules are included in the arms of the MMC to fulfill the fault-safe operation requirement. The performance of the MMC with redundant submodules has not been widely covered in the published literature. This paper investigates the performance of the MMC with redundant submodules in the arms. Two different control strategies are used and compared for integrating redundant submodules. The response of the MMC to a submodule failure for the two strategies is also studied. Moreover, the operation of the MMC with redundant submodules is validated experimentally using the converter prototype in the laboratory.
|
|
| 5. |
- Antonopoulos, Antonios, et al.
(author)
-
Global Asymptotic Stability of Modular Multilevel Converters
- 2014
-
In: IEEE Transactions on Industrial Electronics. - : IEEE. - 0278-0046 .- 1557-9948. ; 61:2, s. 603-612
-
Journal article (peer-reviewed)abstract
- Modular multilevel converters require that the controller is designed so that the submodule capacitor voltages are equalized and stable, independent of the loading conditions. Assuming that the individual capacitor-voltage sharing is managed effectively, an open-loop strategy has been designed to ensure that the total amount of energy stored inside the converter always will be controlled. This strategy, using the steady-state solutions of the dynamic equations for controlling the total stored energy in each converter arm, has proven to be effective. The intention of this paper is to explain in a rigorous way the mechanism behind the suggested strategy and to prove that, when this open-loop strategy is used, the system becomes globally asymptotically stable. Experimental verification on a three-phase 10-kVA prototype is presented.
|
|
| 6. |
- Antonopoulos, Antonios, et al.
(author)
-
Modular multilevel converter AC motor drives with constant torque from zero to nominal speed
- 2014
-
In: IEEE transactions on industry applications. - 0093-9994 .- 1939-9367. ; 50:3, s. 1982-1993
-
Journal article (peer-reviewed)abstract
- Modular multilevel converters are shown to have a great potential in the area of medium-voltage drives. Low-distortion output quantities combined with low average switching frequencies for the semiconductor devices create an ideal combination for very high-efficiency drives. However, the large number of devices and capacitors that have to conduct the fundamental-frequency current require more complex converter control techniques than its two-level counterpart. Special care needs to be taken for starting and operation at low speeds, where the low-frequency current may cause significant unbalance between the submodule capacitor voltages and disturb the output waveforms. In this paper, principles for converter operation with high torque in the whole speed range are investigated. Experimental results from a down-scaled 12-kVA prototype converter running a loaded motor at various speeds between standstill and the rated speed are also provided.
|
|
| 7. |
- Antonopoulos, Antonios, et al.
(author)
-
Optimal selection of the average capacitor voltage for modular multilevel converters
- 2013
-
In: 2013 IEEE Energy Conversion Congress and Exposition, ECCE 2013. - : IEEE. - 9781479903351 ; , s. 3368-3374
-
Conference paper (peer-reviewed)abstract
- Variable-speed drives have reduced voltage requirements when operating below the base speed. In a modular-multilevel-converter-based (M2C-based) motor drive it is then possible to operate with reduced voltage in the submodule capacitors, than at the base speed. In this sense, a greater capacitor-voltage ripple can be accommodated, without exceeding the maximum peak-capacitor voltage. This paper presents an analytical investigation for the optimal selection of the average capacitor voltage for M2Cs, when the motor is operating with rated torque, below the base speed. This method does not require any power exchange between the converter arms, so it keeps the conduction losses at the minimum level. Additionally, the method decreases the switching losses, due to the decreased capacitor-voltage level. The overall ratings of the converter remain the same as in the base-speed operation. It is shown that this method can be applied at a speed range between the base speed and down to approximately one third of it, i.e, an operating range that covers the requirements for typical pump- and fan-type applications. The results obtained from the analytical investigation are experimentally verified on a down-scaled laboratory prototype M2C.
|
|
| 8. |
- Antonopoulos, Antonios, 1984-, et al.
(author)
-
Optimal Selection of the Average Capacitor Voltage for Variable-Speed Drives With Modular Multilevel Converters
- 2015
-
In: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107. ; 30:1, s. 227-234
-
Journal article (peer-reviewed)abstract
- Variable-speed drives have reduced voltage requirementswhen operating below the base speed. In a modularmultilevel-converter-based (M2C-based) motor drive it is thenpossible to operate with reduced voltage in the submodulecapacitors, than at the base speed. In this sense, a greatercapacitor-voltage ripple can be accommodated, without exceedingthe maximum peak-capacitor voltage. This paper presents ananalytical investigation for the optimal selection of the averagecapacitor voltage for M2Cs, when the motor is operating withrated torque, below the base speed. This method does not requireany power exchange between the converter arms, so it keepsthe conduction losses at the minimum level. Additionally, themethod decreases the switching losses, due to the decreasedcapacitor-voltage level. The overall ratings of the converterremain the same as in the base-speed operation. It is shownthat this method can be applied at a speed range betweenthe base speed and down to approximately one third of it,i.e, an operating range that covers the requirements for typicalpump- and fan-type applications. The results obtained from theanalytical investigation are experimentally verified on a downscaledlaboratory prototype M2C.
|
|
| 9. |
- Antonopoulos, Antonios, et al.
(author)
-
Stability Analysis of Modular Multilevel Converters With Open-Loop Control
- 2013
-
In: 39th Annual Conference of the IEEE Industrial Electronics Society, IECON 2013. - : IEEE. - 9781479902248 ; , s. 6316-6321
-
Conference paper (peer-reviewed)abstract
- Modular multilevel converters (M2Cs) require that the controller is designed so that the submodule capacitor voltages are equalized and stable, independent of the loading conditions. Provided that the individual capacitor voltage sharing is managed effectively, an open-loop strategy can been designed to ensure that the total amount of energy stored inside the converter always will be controlled. This strategy, using the steady-state solutions of the dynamic equations for controlling the total stored energy in each converter arm, has proven to be effective. The intention of this paper is to explain in a rigorous way the mechanism behind the suggested strategy, and to prove that, when this open-loop strategy is used, the system becomes globally asymptotically stable.
|
|
| 10. |
- Harnefors, Lennart, et al.
(author)
-
Dynamic Analysis of Modular Multilevel Converters
- 2013
-
In: IEEE Transactions on Industrial Electronics. - 0278-0046 .- 1557-9948. ; 60:7, s. 2526-2537
-
Journal article (peer-reviewed)abstract
- Theory for the dynamics of modular multilevel converters is developed in this paper. It is shown that the sum capacitor voltage in each arm often can be considered instead of the individual capacitor voltages, thereby significantly reducing the complexity of the system model. Two selections of the so-called insertion indices, which both compensate for the sum-capacitor-voltage ripples, are considered. The dynamic systems which respectively result from these selections are analyzed. An effective dc-bus model, which takes into account the contribution from the submodule capacitors, is obtained. Finally, explicit formulas for the stationary sum-capacitor-voltage ripples are derived.
|
|
| 11. |
- Ilves, Kalle, 1984-, et al.
(author)
-
Capacitor Voltage Ripple Shaping in Modular Multilevel Converters Allowing for Operating Region Extension
- 2011
-
In: IECON 2011. - New York : IEEE. - 9781612849720 ; , s. 4403-4408
-
Conference paper (peer-reviewed)abstract
- The second-order harmonic in the circulating current of a modular multilevel converter (M2C) influences the capacitor voltage ripple. If no measures are taken to control it, it is not possible to operate the converter with unity modulation index. An open-loop method that precalculates the instantaneous values of the circulating current and the capacitor voltages is used, in order to control the circulating current. A desired second-order harmonic is intentionally induced in the circulating current in order to make the peak of the capacitor voltage coincide with the maximum requested voltage, aiming either to extend the limits of the instantaneous available voltage or avoid unnecessarily high capacitor voltages. A method for numerical estimation of the appropriate amplitude and phase of the induced second-order harmonic is described. The method is experimentally evaluated on a three-phase down-scaled laboratory prototype. From the experiments it was found that significantly improved operating conditions could be obtained.
|
|
| 12. |
- Nikouei Harnefors, Mojgan, 1983-, et al.
(author)
-
Operation Under Fault Conditions of the Stacked Polyphase Bridges Converter
- 2016
-
Conference paper (peer-reviewed)abstract
- The stacked polyphase bridges converter consists of several submodules that, on the input dc side, all are connected in series. Whereas controller designs presented in previous studies have been found promising for realizing equal voltage sharing between submodules, the survival and stability under fault conditions have not been studied. This paper presents a control strategy that enables survival of the converter after the occurrence of a sudden short circuit of a single transistor switch. The results are verified by simulations.
|
|
| 13. |
- Nikouie Harnefors, Mojgan, et al.
(author)
-
Analysis of the dc-link stability for the stacked polyphase bridges converter
- 2015
-
In: 2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe). - : IEEE.
-
Conference paper (peer-reviewed)abstract
- This paper presents an analysis of the capacitor voltage stability for a stacked polyphase bridges (SPB)type converter. The SPB converter comprises of several submodules which are connected in series.Therefore, stability of the dc-link voltage is very important to investigate. From the analysis, a correspondingcontroller and an analytical expression for stability are derived. The proposed controller andthe associated stability condition are verified in a simulation environment and on a small experimentalsetup.
|
|
| 14. |
- Nikouie Harnefors, Mojgan, et al.
(author)
-
DC-link stability analysis and controller design for the stacked polyphase bridges converter
- 2017
-
In: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 32:2, s. 1666-1674
-
Journal article (peer-reviewed)abstract
- The stacked polyphase bridges (SPB) converter consists of several submodules that all are connected in series to a voltage source. The total dc-link voltage should split in a balanced way among the submodules. This does not always occur inherently. This paper presents an analysis of the capacitor voltage stability for the SPB converter. From the analysis, criteria for stability are derived and three alternatives of a suitable balancing controller are designed. The proposed controller alternatives and their associated stability properties are verified on an experimental setup and by simulation.
|
|
| 15. |
- Norrga, Staffan, 1968-, et al.
(author)
-
Decoupled steady-state model of the modular multilevel converter with half-bridge cells
- 2012
-
Conference paper (peer-reviewed)abstract
- Modular multilevel converters, based on cascading of halfbridge converter cells, can combine low switching frequency with low harmonic interference. They can be designed for high operating voltages without direct series connection of semiconductor elements. This has led to a rapid adoption within high-power applications such as HVDC, STATCOM and railway interties. Analysing the operation of these converters in the frequency domain poses a few challenges due to the presence of significant low-order harmonic voltages in the cell capacitors. This paper presents a frequency-domain model of the MMC converter with halfbridge cells, based on a two-stage approach. First, the circuit equations are decoupled by a simple linear transformation, whereby the circuit schematic can be separated into a dc-side and an ac-side part. Second, the switching operation within the phase arms is modelled in the frequency domain by iterated convolution. The model is verified against a timedomain simulation of a converter with ratings valid for HVDC applications. It is shown that the proposed methodology, where all calculations are made in the frequency domain, can accurately reproduce the results from the simulation.
|
|
| 16. |
- Norrga, Staffan, 1968-, et al.
(author)
-
Frequency-Domain Modeling of Modular Multilevel Converters With Application to Maximizing the Operating Region
- 2012
-
In: IECON 2012 - 38th Annual Conference on IEEE Industrial Electronics Society. - : IEEE. - 9781467324212 ; , s. 4967-4972
-
Conference paper (peer-reviewed)abstract
- Modular multilevel converters (MMC), based on cascading of half-bridge converter cells, can combine low switching frequency with low harmonic interference. They can be designed for high operating voltages without direct series connection of semiconductor elements. This has led to a rapid adoption within high-power applications such as high voltage direct current transmission, railway interties and medium voltage industrial motor drives. Analyzing the operation of these converters in the frequency domain poses a few challenges due to the presence of significant low-order harmonic voltages in the cell capacitors. This paper treats a frequency-domain methodology for computing inner variables of the MMC with half-bridge cells, based on a two-stage approach. First, the circuit equations are decoupled by a simple linear transformation, whereby the circuit schematic can be separated into a dc-side and an ac-side part. Second, the variables of the cell strings are computed in the frequency domain by iterated convolution. It is shown that the proposed methodology, where all calculations are made in the frequency domain, can accurately reproduce the results from a PSCAD simulation. Furthermore, the model is successfully employed as part of an optimization algorithm for maximizing the power handling capability of the converter by appropriately controlling the circulating current and zero-sequence ac-side voltage. Results from this work point to significant possibilities for improvement.
|
|
| 17. |
- Ahmed, Noman, et al.
(author)
-
HVDC SuperGrids with modular multilevel converters - The power transmission backbone of the future
- 2012
-
In: International Multi-Conference on Systems, Signals and Devices, SSD 2012. - : IEEE. - 9781467315906 ; , s. 6198119-
-
Conference paper (peer-reviewed)abstract
- In order to transmit massive amounts of power generated by remotely located power plants, especially offshore wind farms, and to balance the intermittent nature of renewable energy sources, the need for a stronger high voltage transmission grid is anticipated. Due to limitations in ac power transmission the most likable choice for such a grid is a high-voltage dc (HVDC) grid. However, the concept of the HVDC grid is still under active development as different technical challenges exist, and it is not yet possible to construct such a dc grid. This paper deals with prospects and technical challenges for future HVDC SuperGrids. Different topologies for a SuperGrid and the possibility to use modular multilevel converters (M2Cs) are presented. A comprehensive overview of different submodule implementations of M2C is given as well as a discussion on the choice between cables or overhead lines, the protection system for the dc grid and dc-side resonance issues.
|
|
| 18. |
- Ali, Muhammad Taha, et al.
(author)
-
Analysis and Mitigation of SSCI in DFIG Systems With Experimental Validation
- 2020
-
In: IEEE transactions on energy conversion. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0885-8969 .- 1558-0059. ; 35:2, s. 714-723
-
Journal article (peer-reviewed)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.
|
|
| 19. |
- Ali, Muhammad Taha, et al.
(author)
-
Effect of control parameters on infliction of sub-synchronous control interaction in DFIGs
- 2016
-
In: 2016 IEEE International Conference on Power and Renewable Energy (ICPRE). - : IEEE conference proceedings. - 9781509030682 ; , s. 72-78
-
Conference paper (peer-reviewed)abstract
- This research work deals with the analysis of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs). The time-invariant model of the DFIG is linearized to perform eigenvalue analysis and to obtain the participation factor of each state variable for unstable modes. The sensitivity of system eigenvalues related to sub-synchronous modes is analyzed with respect to all the proportional and integral parameters of the controllers in the rotor-side-converters and grid-side-converters. The major contribution of this research work is the outcomes based on eigenvalue analysis that clearly point out the control parameters to which sub-synchronous modes are highly sensitive. The effect of series compensation level on DFIG system and on the sensitivity of converter control parameters is also studied.
|
|
| 20. |
- Ali, Muhammad Taha, et al.
(author)
-
Mitigation of Sub-Synchronous Control Interaction in DFIGs using a Power Oscillation Damper
- 2017
-
In: 2017 IEEE Manchester PowerTech, Powertech 2017. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509042371
-
Conference paper (peer-reviewed)abstract
- The aim of this research work is to analyse subsynchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) and to design a supplementary control technique for the mitigation of SSCI. A mathematical model of the DFIG is derived and linearized in order to perform an eigenvalue analysis. This analysis pinpoints the parameters of the system which are sensitive in making sub-synchronous modes unstable and hence are responsible for causing SSCI. A power oscillation damper (POD) is designed using a residue method to make the DFIG system immune to the SSCI. The POD control signal acts as a supplementary control, which is fed to the controller of the grid-side converter (GSC). The POD signal is applied to different summation junctions of the GSC controller in order to determine the best placement of the POD for effective mitigation of SSCI and for the increased damping of the system.
|
|
| 21. |
- Ali, Muhammad Taha, et al.
(author)
-
Optimal tuning and placement of POD for SSCI mitigation in DFIG-based power system
- 2019
-
In: 2019 IEEE Milan PowerTech, PowerTech 2019. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538647226
-
Conference paper (peer-reviewed)abstract
- The phenomenon of sub-synchronous control interaction (SSCI) in doubly-fed induction generators (DFIGs) is investigated and the optimal tuning and placement of a power oscillation damper (POD) for its mitigation is proposed in this paper. The effect of the POD on the DFIG system is studied by placing it at all the summation junctions of rotor-side converter (RSC) and grid-side converter (GSC) controllers, turn by turn. Five local signals are examined as different input signals to the POD out of which three local signals gave promising results. These signals include the DFIG's active power, the magnitude of the DFIG's apparent power, and the magnitude of the current through the transmission line. Residues are calculated for each POD placement and for each input to the POD. The calculated residues are studied along with the root-locus plots to see the effect of the POD on the mitigation of SSCI and the stability of the DFIG-based system.
|
|
| 22. |
- Antonopoulos, Antonios, 1984-
(author)
-
On the Internal Dynamics and AC-Motor Drive Application of Modular Multilevel Converters
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- This thesis is an effort to investigate the operation and the performanceof modular multilevel converters (M2Cs). Proven to be the most promisingtopology in high-voltage high-power applications, it is necessary to put aneffort in understanding the physical laws that govern the internal dynamicsof such converters, in order to design appropriate control methods. AlthoughM2Cs belong to the well-studied family of voltage-source converters (VSCs),and claim a modular structure, their control is significantly more complicatedcompared to two- or three-level VSCs, due to the fact that a much highernumber of switches and capacitors are needed in such a topology. This thesishighlights the important parameters that should be considered when designingthe control for an M2C, through analyzing its internal dynamics, and alsosuggests ways to control such converters ensuring stable operation withoutcompromising the performance of the converter.Special focus is given on ac motor-drive applications as they are very demandingand challenging for the converter performance. Interactions betweenthe internal dynamics and the dynamics of the driven motor are experimentallyinvestigated. The problem of operating the converter when connectedto a motor standing still is visited, even under the condition that a greatamount of torque and current are requested, in order to provide an idea forthe converter requirements under such conditions. Finally, an optimization ofthe converter operation is suggested in order to avoid overrating the convertercomponents in certain operation areas that this is possible.All analytical investigations presented in this thesis are confirmed by experimentalresults on a laboratory prototype converter, which was developedfor the purposes of this project. Experimental verification proves the validityof the theoretical investigations, as well as the correct performance of thecontrol methods developed during this project on a real, physical converter,hoping that the results of this thesis will be useful for large-scale implementations,in the mega- or even giga-watt power range.
|
|
| 23. |
- Bakas, Panagiotis, 1984-, et al.
(author)
-
A Review of Hybrid Topologies Combining Line-Commutated and Cascaded Full-Bridge Converters
- 2017
-
In: IEEE transactions on power electronics. - : IEEE Press. - 0885-8993 .- 1941-0107. ; 32:10, s. 7435-7448
-
Research review (peer-reviewed)abstract
- This paper presents a review of concepts for enabling the operation of a line-commutated converter (LCC) at leading power angles. These concepts rely on voltage or current injection at the ac or dc sides of the LCC, which can be achieved in different ways. We focus on the voltage and current injection by full-bridge (FB) arms, which can be connected either at the ac or dc sides of the LCC and can generate voltages that approximate ideal sinusoids. Hybrid configurations of an LCC connected at the ac side in series or in parallel with FB arms are presented. Moreover, a hybrid configuration of an LCC connected in parallel at the ac side and in series at the dc side with an FB modular multilevel converter (MMC) is outlined. The main contribution of this paper is an analysis and comparison of the mentioned hybrid configurations in terms of the capability to independently control the active (P) and reactive power (Q).
|
|
| 24. |
- Bakas, Panagiotis, et al.
(author)
-
Design considerations and comparison of hybrid line-commutated and cascaded full-bridge converters with reactive-power compensation and active filtering capabilities
- 2019
-
Conference paper (other academic/artistic)abstract
- This paper compares two hybrid topologies that combine the line-commutated converter (LCC) with cascaded full-bridge (FB) converters. The latter are utilized for compensating the reactive power and filtering the current harmonics of the LCC. The method that was developed for dimensioning these hybrid topologies is presented in detail. This method is utilized for calculating the arm voltage and current waveforms, which are used to estimate other important quantities, such as conduction losses and energy variations. Finally, the studied converters are compared in terms of voltage/current ratings, semiconductor requirements, conduction losses, and energy variations.
|
|
| 25. |
- Bakas, Panagiotis, et al.
(author)
-
Hybrid alternate-common-arm converter with director thyristors - Impact of commutation time on the active-power capability
- 2019
-
In: 2019 21st European Conference on Power Electronics and Applications, EPE 2019 ECCE Europe. - Genova, Italy : Institute of Electrical and Electronics Engineers Inc.. - 9789075815313 - 9781728123615
-
Conference paper (peer-reviewed)abstract
- This paper investigates the impact of the thyristor commutation time on the peak currents and the active-power capability of the hybrid alternate-common-arm converter (HACC). This converter employs director thyristors for the alternate connection of a common arm in parallel to the main arms. The parallel connection enables current sharing among the arms, which allows the HACC to transfer higher output power without increasing the peak arm current. It is shown that the active-power capability of the HACC is doubled for a certain current-sharing factor, which, however, is altered by the thyristor commutation time. Therefore, the impact of the commutation time on the active-power capability of the HACC is investigated theoretically. Finally, this analysis is verified by simulation results.
|
|
| 26. |
- Bakas, Panagiotis, et al.
(author)
-
Hybrid alternate-common-arm converter with high power capability : Potential and limitations
- 2020
-
In: IEEE transactions on power electronics. - : IEEE. - 0885-8993 .- 1941-0107. ; 35:12, s. 12909-12928
-
Journal article (peer-reviewed)abstract
- This paper studies a new hybrid converter thatutilizes thyristors and full-bridge (FB) arms for achieving higherpower capability than the full-bridge (FB) modular multilevel converter (MMC) with reduced semiconductor requirements. The study covers the theoretical analysis of the energy balancing,the dimensioning principles, the maximum power capability, and the limitations imposed by the discontinuous operation of theconverter. Based on the analysis of these aspects, the theoretical analysis is concluded by identifying the design constraints that need to be fulfilled for achieving the maximum power capabilityof the converter. It is concluded that the maximum power capability can be achieved for a certain range of modulation indices and is limited by both the commutation time of the thyristors andthe power angle. Finally, simulation and experimental results that confirm the theoretical analysis and the feasibility of the studied converter are presented and discussed.
|
|
| 27. |
- Bakas, Panagiotis, et al.
(author)
-
Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability
- 2018
-
In: 2018 20th European Conference on Power Electronics and Applications (EPE’18 ECCE Europe).
-
Conference paper (peer-reviewed)abstract
- This paper presents the basic operating principles of a new hybrid converter that combines thyristors and full-bridge (FB) arms for achieving high active-power capability. This converter consists of a modular multilevel converter (MMC) equipped with additional common arms, which alternate between the upper and lower dc poles. This alternation is achieved by the thyristors that are utilized as director switches and allow the parallel connection of the common arms and the arms of the MMC. The main contributions of this paper are the analysis of the operating principles, the simulation verification of the functionality of the proposed converter, and the comparison of the latter with the full-bridge modular multilevel converter (FB-MMC).
|
|
| 28. |
- Bakas, Panagiotis
(author)
-
Hybrid Converters for HVDC Transmission
- 2019
-
Doctoral thesis (other academic/artistic)abstract
- The line-commutated converter (LCC) and the voltage-source converter (VSC) are the two main converter technologies utilized in high-voltage direct current (HVDC) transmission applications. Depending on the application requirements, one technology might be more advantageous than the other. On the one hand, the LCC features technological maturity, high efficiency, and high power-transfer capability, but it lacks the ability to independently control active and reactive power and to ride through ac faults. On the other hand, the VSC overcomes the shortcomings of the LCC and offers more functionality, as it features the ability to independently control active and reactive power, ac-fault ride through capability, black-start capability, and superior harmonic performance. Yet, it is less mature, less efficient, and has lower power-transfer capability than the LCC. Thus, the combination of the LCC and the VSC topologies could yield hybrid converters that leverage the complementary characteristics of both technologies and thus are optimized for HVDC applications. Therefore, the main objective of this thesis is to investigate existing and derive new hybrid converters that combine the complementary characteristics of the LCC and VSC technologies.The hybrid converters investigated in this thesis are divided in two main categories, namely: (a) current-source; and (b) voltage-source hybrid converters. The former category includes hybrid converters that are based on the LCC structure and utilize a VSC part either for compensating the reactive power consumed by the LCC, or for active filtering of the LCC current harmonics, or for independently controlling active and reactive power, or for achieving a combination of these functionalities. Four different current-source hybrid converters have been investigated and compared in terms of functionality, conduction losses, and semiconductor requirements.The second category includes more complex circuits that combine thyristors and modular VSC elements in ways that enable these hybrid converters to operate as VSCs and to achieve high active-power capability. Two new voltage-source hybrid converters are analyzed and compared in terms of active-power capability, semiconductor requirements, and controllability. This study reveals that the hybrid alternate-common-arm converter (HACC) is the most interesting circuit; thus, an in-depth analysis is performed for this converter. The theoretical analysis shows that, under certain operating conditions, the HACC can transfer twice the active power of the full-bridge modular multilevel converter (FB-MMC) with lower semiconductor rating per unit of active power. Yet, if the total commutation time of the thyristors and/or the power angle are increased beyond certain values, the active-power capability of the HACC is reduced. Finally, simulation and experimental results are provided in order to verify the theoretical analysis and prove the feasibility of the HACC.
|
|
| 29. |
- Bakas, Panagiotis, et al.
(author)
-
Hybrid Topologies for Series and Shunt Compensation of the Line-Commutated Converter
- 2016
-
In: 8th International Power Electronics and Motion Control Conference - ECCE Asia, IPEMC 2016-ECCE Asia. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509012107 ; , s. 3030-3035
-
Conference paper (peer-reviewed)abstract
- This paper presents two concepts for enabling the operation of a line-commutated converter (LCC) at leading power angles. The concepts are based on voltage or current injection at the ac side of an LCC, which can be achieved in different ways. However, this paper focuses on the voltage and current injection by series-connected full-bridge cells that can generate voltages that approximate ideal sinusoids. Thus, hybrid configurations of an LCC connected at the ac side in series or in parallel with fullbridge cells are presented. Finally, these hybrid configurations are compared in terms of voltage and current rating.
|
|
| 30. |
- Bessegato, Luca, et al.
(author)
-
A Method for the Calculation of the AC-Side Admittance of a Modular Multilevel Converter
- 2018
-
In: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107.
-
Journal article (peer-reviewed)abstract
- Connecting a modular multilevel converter to anac grid may cause stability issues, which can be assessed byanalyzing the converter ac-side admittance in relation to the gridimpedance. This paper presents a method for calculating theac-side admittance of modular multilevel converters, analyzingthe main frequency components of the converter variables individually.Starting from a time-averaged model of the converter,the proposed method performs a linearization in the frequencydomain, which overcomes the inherent nonlinearities of theconverter internal dynamics and the phase-locked loop usedin the control. The ac-side admittance obtained analytically isfirstly validated by simulations against a nonlinear time-averagedmodel of the modular multilevel converter. The tradeoff posedby complexity of the method and the accuracy of the result isdiscussed and the magnitude of the individual frequency componentsis shown. Finally, experiments on a down-scaled prototypeare performed to validate this study and the simplification onwhich it is based.
|
|
| 31. |
- Bessegato, Luca, et al.
(author)
-
Ac-side admittance calculation for modular multilevel converters
- 2017
-
In: 2017 IEEE 3rd International Future Energy Electronics Conference and ECCE Asia, IFEEC - ECCE Asia 2017. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781509051571 ; , s. 308-312
-
Conference paper (peer-reviewed)abstract
- Power electronic converters may interact with the grid, thereby influencing dynamic behavior and resonances. Impedance and passivity based stability criteria are two useful methods that allow for studying the grid-converter system as a feedback system, whose behavior is determined by the ratio of grid and converter impedances. In this paper, the ac-side admittance of the modular multilevel converter is calculated using harmonic linearization and considering five specific frequency components of the converter variables. The proposed model features remarkable accuracy, verified through simulations, and insight into the influence of converter and control parameters on the admittance frequency characteristics, which is useful for understanding grid-converter interaction and designing the system.
|
|
| 32. |
- Bessegato, Luca, 1989-, et al.
(author)
-
Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies
- 2020
-
In: IEEE transactions on power electronics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0885-8993 .- 1941-0107. ; 35:3, s. 2411-2423
-
Journal article (peer-reviewed)abstract
- Modular multilevel converters (MMCs) can be configured to perform ac/ac conversion, which makes them suitable as railway power supplies. In this paper, a hierarchical control scheme for ac/ac MMCs for railway power supplies is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. These models allow for analyzing the stability of the interconnected system using the impedance-based stability criterion and the passivity-based stability assessment. Finally, the findings presented in this paper are validated experimentally, using a down-scaled MMC.
|
|
| 33. |
- Bessegato, Luca, et al.
(author)
-
Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies
- 2019
-
In: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107.
-
Journal article (peer-reviewed)abstract
- Modular multilevel converters (MMCs) can be configured to perform ac/ac conversion, which makes them suitable as railway power supplies. In this paper, a hierarchical control scheme for ac/ac MMCs for railway power supplies is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. These models allow for analyzing the stability of the interconnected system using the impedance-based stability criterion and the passivity-based stability assessment. Finally, the findings presented in this paper are validated experimentally, using a down-scaled MMC.
|
|
| 34. |
- Bessegato, Luca, et al.
(author)
-
Control of Direct AC/AC Modular Multilevel Converters Using Capacitor Voltage Estimation
- 2016
-
In: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE). - : IEEE.
-
Conference paper (peer-reviewed)abstract
- This paper applies a control method based on current control and sum-capacitor-voltage estimation to the direct ac/ac modular multilevel converter. As capacitor voltages are estimated, their measurements are not needed in the high-level control, which simplifies the communication between the main controller and the submodules of the converter. The stability of the internal dynamics of the converter, using the aforementioned control method, is studied using Lyapunov stability theory, proving that the system is globally asymptotically stable. The behavior of the converter is simulated focusing on three-phase 50 Hz to single-phase 16 (2)/(3) Hz conversion, which is typical for railway power supply systems of some European countries. Simulation results are in agreement with the expected behavior of the converter, both in steady-state and dynamic situations.
|
|
| 35. |
- Bessegato, Luca, et al.
(author)
-
Control of Modular Multilevel Matrix Converters Based on Capacitor Voltage Estimation
- 2016
-
In: IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), 2016. - : IEEE. - 9781509012107 ; , s. 3447-3452
-
Conference paper (peer-reviewed)abstract
- In this paper, a control method based on capacitor voltage estimation is applied to the modular multilevel matrix converter topology. By using such control method, capacitor voltage measurement is not needed in the high-level control. A state-space model of the converter and the control method is developed. Lyapunov stability theory is used to prove global asymptotic stability of the internal dynamics of the converter. Simulation results showing the behavior of the converter in steady-state and dynamic situations are presented.
|
|
| 36. |
- Bessegato, Luca, et al.
(author)
-
Effects of Control on the AC-Side Admittance of a Modular Multilevel Converter
- 2019
-
In: IEEE transactions on power electronics. - : IEEE Press. - 0885-8993 .- 1941-0107. ; 34:8, s. 7206-7220
-
Journal article (peer-reviewed)abstract
- The stability of a modular multilevel converter connected to an ac grid can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. The converter control parameters have a strong impact on the admittance and they can be adjusted for achieving system stability. This paper focuses on the admittance-shaping effect produced by different current-control schemes, either designed on a per-phase basis or in the $dq$ frame using space vectors. A linear analytical model of the converter ac-side admittance is developed, including the different current-control schemes and the phase-locked loop. Different solutions for computing the insertion indices are also analyzed, showing that for a closed-loop scheme a compact expression of the admittance is obtained. The impact of the control parameters on the admittance is discussed and verified experimentally, giving guidelines for designing the system in terms of stability. Moreover, recommendations on whether a simplified admittance expression could be used instead of the detailed model are given. The findings from the admittance-shaping analysis are used to recreate a grid-converter system whose stability is determined by the control parameters. The developed admittance model is then used in this experimental case study, showing that the stability of the interconnected system can be assessed using the Nyquist stability criterion.
|
|
| 37. |
- Bessegato, Luca, 1989-
(author)
-
Modeling of Modular Multilevel Converters for Stability Analysis
- 2019
-
Doctoral thesis (other academic/artistic)abstract
- Modular multilevel converters (MMCs) have recently become the state-of-the-art solution for various grid-connected applications, such as high-voltage direct current (HVDC) systems and flexible alternating current transmission systems (FACTS). Modularity, scalability, low power losses, and low harmonic distortion are the outstanding properties that make MMCs a key technology for a sustainable future. The main objective of this thesis is the modeling of grid-connected MMCs for stability analysis. The stability of the interconnected system, formed by the converter and the ac grid, can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. Therefore, a method for the calculation of the ac-side admittance of MMCs is developed. This method overcomes the nonlinearities of the converter dynamics and it can be easily adapted to different applications. Moreover, the effects of different control schemes on the MMC ac-side admittance are studied, showing how the converter admittance can be reshaped. This is a useful tool for system design, because it shows how control parameters can be selected to avoid undesired grid-converter interactions. This thesis also studies ac/ac MMCs for railway power supplies, which are used in countries with a low-frequency railway grid, such as Germany (16.7 Hz) and Sweden (16 2/3 Hz). A hierarchical control scheme for these converters is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. For computing the insertion indices, an open-loop scheme with sum capacitor voltage estimation is applied to the ac/ac MMC. Lyapunov stability theory is used to prove the asymptotic stability of the converter operated with the proposed control method. This specific open-loop scheme is also adapted to a modular multilevel matrix converter, which performs three-to-three phase direct conversion. Finally, this thesis presents the design of a down-scaled MMC prototype for experimental verification, rated at 10 kW with 30 full-bridge submodules. The hardware and the software are designed to be easily reconfigurable, which makes the converter suitable for different research projects focused on MMCs. Experiments on this down-scaled MMC are used to support and validate the key results presented throughout the thesis.
|
|
| 38. |
- Bidadfar, Ali, et al.
(author)
-
Power System Stability Analysis Using Feedback Control System Modeling Including HVDC Transmission Links
- 2016
-
In: IEEE Transactions on Power Systems. - : IEEE. - 0885-8950 .- 1558-0679. ; 31:1, s. 116-124
-
Journal article (peer-reviewed)abstract
- A general platform is introduced to study the dynamics of power systems with high voltage dc (HVDC) transmission links. Small-signal stability, voltage stability, and interaction phenomena of power systems with both line-commutated-converter HVDC (LCC-HVDC) and voltage-source-converter HVDC (VSC-HVDC) are addressed using the proposed platform. In this platform, the entire power system is modeled as a multivariable feedback control system (FCS) which consists of three interconnected blocks. The contents as well as the inputs and outputs of the blocks are selected such that the conventional analysis tools for power system stability are applicable, both in the time and frequency domains. In the FCS model, the relationships between different instabilities are clear, and participant agents of each instability can be determined. The model is developed in a modular and hybrid style, to make it feasible for a large power system. The proposed model is validated against an electromagnetic transient simulation program (PSCAD) using time responses.
|
|
| 39. |
- Björk, Joakim, et al.
(author)
-
Analysis of Coordinated HVDC Control for Power Oscillation Damping
- 2018
-
In: Conference Record of the 3rd IEEE International Workshop on Electronic Power Grid, eGrid 2018. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538676653 ; , s. 19-24
-
Conference paper (peer-reviewed)abstract
- Controlling the active power of high-voltage de (HVDC) transmission that interconnects two asynchronous ac grids can be used to improve the power oscillation damping in both of the interconnected ac systems. Using one HVDC link, achievable performance are limited since control actions may excite modes of similar frequencies in the assisting network. However, with coordinated control of two or more HVDC links, the limitations can be circumvented. With decoupling control the system interactions can be avoided all together. This paper investigates the conditions suitable for decoupling control. It is also shown that decoupling between system modes can be achieved using a proportional controller. The control method is compared to decentralized and H-2 optimal control. The best control method for different system topologies is investigated by looking on input usage and stability following dc link failure.
|
|
| 40. |
- Björk, Joakim, 1989-
(author)
-
Fundamental Control Performance Limitations for Interarea Oscillation Damping and Frequency Stability
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- With the transition towards renewable energy and the deregulation of the electricity markets, the power system is changing. Growing electricity demand and more intermittent power production increase the need for transfer capacity. Lower inertia levels due to a higher share of renewables increase the need for fast frequency reserves (FFR). In this thesis, we study fundamental control limitations for improving the damping of interarea oscillations and frequency stability.The first part of the thesis considers the damping of oscillatory interarea modes. These system-wide modes involve power oscillating between groups of generators and are sometimes hard to control due to their scale and complexity. We consider limitations of decentralized control schemes based on local measurements, as well as centralized control schemes with limitations associated to actuator dynamics and network topology. It is shown that the stability of asynchronous grids can be improved by modulating the active power of a single interconnecting high-voltage direct current (HVDC) link. One challenge with modulating HVDC active power is that the interaction between interarea modes of the two grids may have a negative impact on system stability. By studying the controllability Gramian, we show that it is possible to improve the damping in both grids as long as the frequencies of their interarea modes are not too close. It is demonstrated how the controllability, and therefore the achievable damping, deteriorates as the frequency difference becomes small. With a modal frequency difference of 5%, the damping can be improved by around 2 percentage points whereas a modal frequency difference of 20% allows for around 8 percentage points damping improvement. The results are validated by simulating two HVDC-interconnected 32-bus power system models. We also consider the coordinated control of two and more HVDC links. For some network configurations, it is shown that the interaction between troublesome interarea modes can be avoided. The second part considers the coordination of frequency containment reserves (FCR) in low-inertia power systems. A case study is performed in a 5-machine model of the Nordic synchronous grid. We consider a low-inertia test case where FCR are provided by hydro power. The non-minimum phase characteristic of the waterways limits the achievable bandwidth of the FCR control. It is shown that a consequence of this is that hydro-FCR fails at keeping the frequency nadir above the 49.0 Hz safety limit following the loss of a HVDC link that imports 1400 MW. To improve the dynamic frequency stability, FFR from wind power is considered. For this, a new wind turbine model is developed. The turbine is controlled at variable-speed, enabling FFR by temporarily borrowing energy from the rotating turbine. The nonlinear wind turbine dynamics are linearized to facilitate a control design that coordinate FFR from the wind with slow FCR from hydropower. Complementary wind resources with a total rating of 2000 MW, operating at 70–90% rated wind speeds, is shown to be more than enough to fulfill the frequency stability requirements. The nadir is kept above 49.0 Hz without the need to install battery storage or to waste wind energy by curtailing the wind turbines.
|
|
| 41. |
- Björk, Joakim, et al.
(author)
-
Fundamental Performance Limitations in Utilizing HVDC to Damp Interarea Modes
- 2019
-
In: IEEE Transactions on Power Systems. - : IEEE. - 0885-8950 .- 1558-0679. ; 34:2, s. 1095-1104
-
Journal article (peer-reviewed)abstract
- This paper considers power oscillation damping (POD) using active power modulation of high-voltage dc transmissions. An analytical study of how the proximity between interarea modal frequencies in two interconnected asynchronous grids puts a fundamental limit to the achievable performance is presented. It is shown that the ratio between the modal frequencies is the sole factor determining the achievable nominal performance. To illustrate the inherent limitations, simulations using a proportional controller tuned to optimize performance in terms of POD are done on a simplified two-machine model. The influence of limited system information and unmodeled dynamics is shown. The analytical result is then further validated on a realistic model with two interconnected 32-bus networks.
|
|
| 42. |
- Björk, Joakim, et al.
(author)
-
Influence of Sensor Feedback Limitations on Power Oscillation Damping and Transient Stability
- 2022
-
In: IEEE Transactions on Power Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8950 .- 1558-0679. ; 37:2, s. 901-912
-
Journal article (peer-reviewed)abstract
- Fundamental sensor feedback limitations for improving rotor angle stability using local frequency or phase angle measurement are derived. Using a two-machine power system model, it is shown that improved damping of inter-area oscillations must come at the cost of reduced transient stability margins, regardless of the control design method. The control limitations stem from that the excitation of an inter-area mode by external disturbances cannot be estimated with certainty using local frequency information. The results are validated on a modified Kundur four-machine two-area test system where the active power is modulated on an embedded high-voltage dc link. Damping control using local phase angle measurements, unavoidably leads to an increased rotor angle deviation following certain load disturbances. For a highly stressed system, it is shown that this may lead to transient instability. The limitations derived in the paper may motivate the need for wide-area measurements in power oscillation damping control.
|
|
| 43. |
- Björk, Joakim, 1989-
(author)
-
Performance Quantification of Interarea Oscillation Damping Using HVDC
- 2019
-
Licentiate thesis (other academic/artistic)abstract
- With the transition towards renewable energy, and the deregulation of the electricity market, generation patterns and grid topology are changing. These changes increase the need for transfer capacity. One limiting factor, which sometimes leads to underutilization of the transmission grid, is interarea oscillations. These system-wide modes involve groups of generators oscillating relative to each other and are sometimes hard to control due to their scale and complexity. In this thesis we investigate how high-voltage direct current (HVDC) transmission can be used to attenuate interarea oscillations. The thesis has two main contributions.In the first contribution we show how the stability of two asynchronous grids can be improved by modulating the active power of a single interconnecting HVDC link. One concern with modulating HVDC active power is that the interaction between interarea modes of the two grids may have a negative impact on system stability. By studying the controllability Gramian, we show that it is always possible to improve the damping in both grids as long as the frequencies of their interarea modes are not too close. For simplified models, it is explicitly shown how the controllability, and therefore the achievable damping improvements, deteriorates as the frequency difference becomes small.The second contribution of the thesis is to show how coordinated control of two (or more) links can be used to avoid interaction between troublesome interarea modes. We investigate the performance of some multivariable control designs. In particular we look at input usage as well as robustness to measurement, communication, and actuator failures. Suitable controllers are thereby characterized.
|
|
| 44. |
- Chen, Feifan, et al.
(author)
-
Dynamics Enhancement for Power Synchronization Control with Asymmetric AC Voltage Controller in Strong Grids
- 2023
-
In: 2023 IEEE Conference on Control Technology and Applications, CCTA 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1066-1070
-
Conference paper (peer-reviewed)abstract
- Power synchronization control (PSC) is designed for weak grid connections originally and its performance is weakened when connected to a strong grid. In this paper, an asymmetric AC voltage controller (AVC) is proposed to improve the performance of PSC in strong grids. The improvement is achieved by adding a coupling from d-axis to q-axis to the voltage control part. The effect of this d-to-q coupling is explained by small signal modeling. It is found that the asymmetric AVC gives an effective improvement in damping the low-frequency oscillation and stability robustness against the grid strengths. Theoretical analysis and experiments verify the effectiveness of the proposed asymmetric AVC.
|
|
| 45. |
- Chen, Feifan, et al.
(author)
-
Enhanced Q-Axis Voltage-Integral Damping Control for Fast PLL-Synchronized Inverters in Weak Grids
- 2024
-
In: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 39:1, s. 424-435
-
Journal article (peer-reviewed)abstract
- The phase-locked loop (PLL) is a commonly used synchronization control method for grid-tied inverters. The PLL-synchronized inverters tend to have poor stability robustness with weak grid interconnections, especially when the PLL is designed with a high control bandwidth. To tackle this challenge, this article proposes an enhanced q-axis voltage-integral damping control, which not only stabilizes PLL-synchronized inverters in weak grids but also lifts the restriction on PLL bandwidth. This superior feature enables inverters to operate stably in ultraweak grids and with a superior transient response. The experimental tests confirm the performance of the method with 400-Hz PLL bandwidth under a short-circuit ratio of 1.28 of the grids.
|
|
| 46. |
- Chen, Feifan, et al.
(author)
-
Impedance Modeling for Quadrature-Axis Active Damping of PLL Dynamics
- 2022
-
In: 2022 IEEE 23RD WORKSHOP ON CONTROL AND MODELING FOR POWER ELECTRONICS (COMPEL 2022). - : IEEE.
-
Conference paper (peer-reviewed)abstract
- When grid-following voltage source converters (VSCs) operate in inverter mode, the phase-locked loop (PLL) dynamics introduce a negative-real-part impedance, which may lead to the instability of the closed-loop system, especially in a weak-grid connection. This undesirable property of the PLL may be offset by so-called active damping. Nevertheless, the interaction between the active damping and the adverse PLL impact is not fully understood. To this end, the properties of different active-damping methods are analyzed, with the focus on the q-to-q coupling of the input admittance. One important finding is that adding an integrator to the q-axis active damper can improve the system performance in a weak-grid connection. Simulations and experimental results verify the theoretical analysis.
|
|
| 47. |
- Chen, Feifan, et al.
(author)
-
Pitfalls of Using Passivity Index to Guide Grid-connected Inverter Control Design in Low-frequency Region
- 2023
-
In: 2023 IEEE Energy Conversion Congress and Exposition, ECCE 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 758-764
-
Conference paper (peer-reviewed)abstract
- The main purpose of this article is to elaborate on the pitfalls of using the frequency-domain passivity theories in grid-inverter interactions within the low-frequency range. It mainly covers the relationship between the passivity index and stability, considerations for control design guided by optimizing the passivity index, and issues with a negative infinite index. It is advised to exercise caution when applying passivity theory in the low-frequency range. These conclusions have been substantiated through numerical and experimental studies.
|
|
| 48. |
- Ciftci, Baris, et al.
(author)
-
Wireless control of modular multilevel converter autonomous submodules : 23rd European Conference on Power Electronics and Applications
- 2021
-
In: Proceedings 23rd European Conference on Power Electronics and Applications. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- The wireless control of modular multilevel converter (MMC) submodules might offer advantages for MMCs with a high number of submodules. However, the control system should tolerate the stochastic nature of the wireless communication, continue the operation flawlessly or, at least, avoid overcurrents, overvoltages, and component failures. The previously proposed control methods enabled to control the submodules wirelessly with consecutive communication errors up to hundreds of control cycles. The submodule control method in this paper facilitates the MMC to safely overcome communication errors that last longer and when the MMC experiences significant electrical disturbances during the errors. The submodules are proposed to operate autonomously by implementing a replica of the central controller in the submodules and drive the replicas based on the local variables and the previously received data. The simulation and experimental results verify the proposed control method.
|
|
| 49. |
- Ciftci, Baris, et al.
(author)
-
Wireless Control of Modular Multilevel Converter Submodules
- 2021
-
In: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 36:7, s. 8439-8453
-
Journal article (peer-reviewed)abstract
- Wireless control of modular multilevel converter (MMC) submodules offers several potential benefits to exploit, such as decreased converter costs and ease in converter installation. However, wireless control comes with several challenging engineering requirements. The control methods used with wired communication networks are not directly applicable to the wireless control due to the latency and reliability differences of wired and wireless networks. This article reviews the existing control architectures of MMCs and proposes a control and communication method for wireless submodule control. Also, a synchronization method for pulsewidth modulation carriers is proposed suitable for wireless control. The imperfections of wireless communication, such as higher latency and packet losses compared to wired communication, are analyzed for the operation of MMCs. The latency is fixed with a proper controller and wireless network design. The converter is rendered immune to the packet losses by decreasing the closed-loop control bandwidth. The functionality of the proposal is verified, for the first time, experimentally on a laboratory-scale MMC using a simple wireless network. It is shown that wireless control of MMC submodules with the proposed approach can perform comparably to the wired control.
|
|
| 50. |
- Ciftci, Baris, 1987-
(author)
-
Wireless Control of Modular Multilevel Converter Submodules
- 2022
-
Doctoral thesis (other academic/artistic)abstract
- The modular multilevel converter (MMC) has extensively been used in high-voltage, high-power applications such as high-voltage dc transmission systems and flexible alternating current transmission systems. The control of MMC submodules is conventionally realized using wired communication systems. However, MMCs in high-power applications consist of up to thousands of submodules. Significant issues arise with the wired communication systems in the MMC valve halls of these applications, including considerable workforce and time requirements for the cable deployment.The main objective of this thesis is to propose a wireless control method for MMC submodules. Wireless communication has fundamental differences from wired communication regarding latency and reliability. Since the control of submodules is a time-critical process, the MMC internal control and modulation methods used with wired communication systems are not directly applicable to wireless communication systems.A wireless control method is proposed for the MMC submodules. The proposal is based on the distributed control of MMCs, where the control and modulation tasks are shared between a central controller and the submodule controllers. The fundamental data to transmit wirelessly is the insertion indices for each of the MMC arms and the synchronization signal for the modulation carriers generated in the submodules. The amount and the cycle time of the time-critical wireless data are in the range of tens of bytes and hundreds of microseconds and are independent of the total number of submodules. The proposal is experimentally verified on a laboratory-scale MMC.The original proposal is enhanced against the communication errors such that the submodules suffering from the errors can continue their modulation smoothly and uninterruptedly. If continuing the modulation is not feasible in case of very long-lasting communication errors, the submodules switch to a safe operation mode to avoid faults in the MMC. Moreover, wireless control of submodules with ac-side faults is analyzed. The MMC rides through the ac-side faults even with a complete loss of communication before or after the fault instant.A wireless communication network based on 5G New Radio is designed theoretically for an example full-scale MMC valve hall according to the proposed wireless control method. It is evaluated that the latency and reliability of the proposed communication solution can correspond to the proposed wireless control method requirements. Finally, the electromagnetic interference from the MMC submodules is measured as below 500 MHz, which does not affect a wireless communication held in the multi-GHz range.
|
|
