| 1. |
- Bakas, Panagiotis, et al.
(författare)
-
Design considerations and comparison of hybrid line-commutated and cascaded full-bridge converters with reactive-power compensation and active filtering capabilities
- 2019
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)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.
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| 2. |
- Bakas, Panagiotis, et al.
(författare)
-
Hybrid alternate-common-arm converter with director thyristors - Impact of commutation time on the active-power capability
- 2019
-
Ingår i: 2019 21st European Conference on Power Electronics and Applications, EPE 2019 ECCE Europe. - Genova, Italy : Institute of Electrical and Electronics Engineers Inc.. - 9789075815313 - 9781728123615
-
Konferensbidrag (refereegranskat)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.
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| 3. |
- Bakas, Panagiotis, et al.
(författare)
-
Hybrid Converter With Alternate Common Arm and Director Thyristors for High-Power Capability
- 2018
-
Ingår i: 2018 20th European Conference on Power Electronics and Applications (EPE’18 ECCE Europe).
-
Konferensbidrag (refereegranskat)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).
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| 4. |
- Bakas, Panagiotis
(författare)
-
Hybrid Converters for HVDC Transmission
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
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| 5. |
- Bessegato, Luca, et al.
(författare)
-
A Method for the Calculation of the AC-Side Admittance of a Modular Multilevel Converter
- 2018
-
Ingår i: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107.
-
Tidskriftsartikel (refereegranskat)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.
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| 6. |
- Bessegato, Luca, et al.
(författare)
-
Ac-side admittance calculation for modular multilevel converters
- 2017
-
Ingår i: 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
-
Konferensbidrag (refereegranskat)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.
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| 7. |
- Bessegato, Luca, et al.
(författare)
-
Control and Admittance Modeling of an AC/AC Modular Multilevel Converter for Railway Supplies
- 2019
-
Ingår i: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107.
-
Tidskriftsartikel (refereegranskat)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.
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| 8. |
- Bessegato, Luca, et al.
(författare)
-
Effects of Control on the AC-Side Admittance of a Modular Multilevel Converter
- 2019
-
Ingår i: IEEE transactions on power electronics. - : IEEE Press. - 0885-8993 .- 1941-0107. ; 34:8, s. 7206-7220
-
Tidskriftsartikel (refereegranskat)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.
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| 9. |
- Bessegato, Luca, 1989-
(författare)
-
Modeling of Modular Multilevel Converters for Stability Analysis
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
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| 10. |
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| 11. |
- Angquist, Lennart, et al.
(författare)
-
Low-Cost Ultra-Fast DC Circuit-Breaker Power electronics integrated with mechanical switchgear
- 2018
-
Ingår i: 2018 IEEE INTERNATIONAL CONFERENCE ON INDUSTRIAL TECHNOLOGY (ICIT). - : IEEE. - 9781509059492 ; , s. 1708-1713
-
Konferensbidrag (refereegranskat)abstract
- The paper describes a concept for fast-acting circuit-breaker using vacuum interrupter (VI) assisted by a power-electronic converter with low output voltage. The converter excites a passive resonant circuit to create current zero-crossing in the arc in the VI to make it extinguish the current. A fast-acting actuator using a Thomson coil separates the contacts in a few milliseconds. The principle is outlined, and a laboratory prototype is described. In experiments 10 kA was successfully interrupted against 9 kV in 3 ms.
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| 12. |
- Augustin, Tim, et al.
(författare)
-
Modelling of HVDC breakers for HVDC grid simulations
- 2017
-
Ingår i: IET Conference Publications. - : Institution of Engineering and Technology.
-
Konferensbidrag (refereegranskat)abstract
- This paper deals with the modelling of high-voltage direct current (HVDC) breakers in PSCAD. The models are aimed at HVDC grid simulation and are kept as simple as possible. An overview is given over recently proposed HVDC breaker concepts. Assumptions and simplifications are explained as well. The main result is that even these simplified models are too detailed for grid simulations. The reason for this is that from a grid perpective the only thing that matters is when the metal-oxide varistor is inserted. The models can be used to estimate interruption times.
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| 13. |
- Augustin, Tim, et al.
(författare)
-
Transient Behaviour of VSC-HVDC Links with DC Breakers Under Faults
- 2017
-
Ingår i: 2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE EUROPE). - : Institute of Electrical and Electronics Engineers (IEEE). - 9789075815276
-
Konferensbidrag (refereegranskat)abstract
- In future high-voltage direct current (HVDC) systems, a large number of HVDC breakers will be required.In this paper, the influence of HVDC breakers on the transient performance of point-to-point HVDC links in both asymmetrical and symmetrical monopolar configuration with half-bridge modular multilevel converters is studied with simulations in PSCAD. As HVDC breakers, the active resonant breaker and ABB’s hybrid breaker are considered. The analyzed scenarios include DC line faults, DC bus faults, and AC faults between the converter and the transformer. The highest DC breaking capability is required during DC line faults in the asymmetric and symmetric monopole. The converter stress is highest for DC bus faults and unbalanced converter AC faults in the asymmetric monopole and for DC bus pole-to-pole faults in the symmetric monopole. During DC pole-to-ground faults in the symmetric monopole, the HVDC breaker combined with DC side arrestors yields the lowest overvoltage stress on the cable of the healthy pole. The fault current shapes depend strongly on the interaction of the converter and the travelling waves on the lines, and differ from the fault current shapes in typical HVDC breaker test circuits. Furthermore, the active resonant breaker and the ABB hybrid breaker perform similarly in the used benchmarks due to the very fast DC line fault detection.
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| 14. |
- Baudoin, Antoine, et al.
(författare)
-
Experimental results from a Thomson-coil actuator for a vacuum interrupter in an HVDC breaker
- 2019
-
Ingår i: The Journal of Engineering. - : INST ENGINEERING TECHNOLOGY-IET. - 2051-3305. ; :17, s. 3527-3531
-
Tidskriftsartikel (refereegranskat)abstract
- Recent developments in high-voltage direct current transmission technology and the plans for multi-terminals motivate research efforts on the fast DC breaker. A novel concept to interrupt current up to several kiloamperes within a few milliseconds is presently under development, using a vacuum interrupter together with power electronics to create an artificial zero-crossing in the current through the switch. To achieve this objective, one critical component in the concept is an ultra-fast linear mechanical actuator. A prototype has been developed based on a Thomson coil. The experimental results are presented and show how a contact gap in a vacuum interrupter was effectively created in a controlled manner. Current of several kiloamperes was successfully interrupted within 3ms, thanks to the high-speed operation of the linear actuator.
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| 15. |
- Bessegato, Luca, et al.
(författare)
-
Control of Direct AC/AC Modular Multilevel Converters Using Capacitor Voltage Estimation
- 2016
-
Ingår i: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE). - : IEEE.
-
Konferensbidrag (refereegranskat)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.
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| 16. |
- Bessegato, Luca, et al.
(författare)
-
Control of Modular Multilevel Matrix Converters Based on Capacitor Voltage Estimation
- 2016
-
Ingår i: IEEE 8th International Power Electronics and Motion Control Conference (IPEMC-ECCE Asia), 2016. - : IEEE. - 9781509012107 ; , s. 3447-3452
-
Konferensbidrag (refereegranskat)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.
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| 17. |
- Bessegato, Luca, et al.
(författare)
-
Design of a Modular Multilevel Converter Prototype for Research Purposes
- 2018
-
Konferensbidrag (refereegranskat)abstract
- As modular multilevel converters gradually become the preferred topology for many high-voltage andhigh-power applications, they are widely studied among researchers, who need experimental results tovalidate their studies. This paper discusses the design of a down-scaled modular multilevel converterprototype for research purposes, equipped with 30 full-bridge submodules and 10 kW rating. The designof this prototype is aimed at safety, flexibility, orderliness, and compactness. The challenges posed by theimplementation of the converter prototype are examined, discussing the design of the prototype structure,the communication scheme, the full-bridge submodules, and the control hierarchy. The control systemis based on Xilinx Zynq system-on-chip, which integrates programmable logic and processing system,allowing for extensive computational capability as well as simple reconfiguration. Experimental resultsshowing the prototype in operation at nominal ratings are presented along with the devised graphical userinterface.
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| 18. |
- Blinov, Andrei, et al.
(författare)
-
Soft-Switching Modulation Method for Full-Bridge DC-AC HF-Link Inverter
- 2019
-
Ingår i: 45th annual conference of the ieee industrial electronics society (IECON 2019). - : IEEE. - 9781728148786 ; , s. 4417-4422
-
Konferensbidrag (refereegranskat)abstract
- This paper presents an improved modulation method for the cycloconverter stage of high frequency-link DC-AC inverters. By applying the quasi-resonant commutation mode during the entire operating period, the fast and reliable discharge of DC-side capacitances can be provided even if the output current is close to zero. This allows to ensure zero voltage switching (ZVS) conditions for the DC-side transistors, while applying small external snubber capacitors to reduce their turn-off losses. The proposed modulation strategy was significantly simplified and requires no external active auxiliary circuits or multi-mode operation. Moreover, two of the AC-side switches can operate at the fundamental frequency, while the rest operate with zero current switching (ZCS). The proposed modulation method is verified with mathematical analysis, simulation model and experimental prototype of full-bridge HF-link inverter.
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| 19. |
- Chaffey, Geraint, et al.
(författare)
-
Requirements for functional testing of HVDC protection IEDs
- 2019
-
Konferensbidrag (refereegranskat)abstract
- Development of Intelligent Electronic Devices (IED) for HVDC protection is underway, driven in part by the prospective demands of future multiterminal HVDC systems. There is, however, no consensus on how to test the functionality of an HVDC protection IED. Successful operation of a future multivendor HVDC protection system requires functional specifications and harmonised test procedures for protection system components, including the protection IED. This paper presents an introduction to functional testing methods for HVDC protection IEDs. Evaluating the protection algorithm characteristic using synthetic waveforms is first performed, i.e. ’functional type testing’. Given that test procedures are in part dependent on the protection algorithm, tests are developed and presented for several algorithms. The behaviour of the IED in a power system simulation is then examined during generalised yet representative fault transients, i.e. equivalent to ’dynamic validation type testing’ of AC protection algorithms. The combination of functional and dynamic validation type testing allows the generalised functionality of the IED to be evaluated - testing the algorithm, hardware and software implementation, and overall performance. To provide examples of test procedures, an open-source HVDC IED prototype is tested in a hardware-in-the-loop configuration using a real-time simulator. The operation and accuracy of the protection characteristics are first examined, before the IED performance under representative waveforms is determined. Through tests of several non-unit line protection algorithms, it is shown that, depending on the algorithm applied, the IED is dependable for simulated faults within the protection zone, and secure during external faults. Moreover,the test configurations and procedures required to evaluate the functionality and the criteria for success are developed.
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| 20. |
- Chaffey, Geraint, et al.
(författare)
-
The Impact of Point-to-Point VSC-HVDC Protection on Short-Term AC System Voltage
- 2018
-
Ingår i: 2018 IEEE pes innovative smart grid technologies conference europe (ISGT-EUROPE). - : IEEE.
-
Konferensbidrag (refereegranskat)abstract
- Whilst point-to-point HVDC systems are presently protected from DC-side faults using circuit breakers at the AC-side of the converter stations, converters are unable to provide reactive power support to the AC system during the fault clearance. Implementing DC circuit breakers within the HVDC system could result in several benefits, including the near-continuous provision of reactive power to the AC systems. This paper compares HVDC system protection sequences using AC-side and DC-side protection, and evaluates the impact of these protection strategies on the AC voltage under varying AC-system configurations and varying power flow conditions.
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| 21. |
- Ciftci, Baris, 1987-, et al.
(författare)
-
A Proposal for Wireless Control of Submodules in Modular Multilevel Converters
- 2018
-
Konferensbidrag (refereegranskat)abstract
- The modular multilevel converter is one of the most preferred converters for high-power conversion applications. Wireless control of the submodules can contribute to its evolution by lowering the material and labor costs of cabling and by increasing the availability of the converter. However, wireless control leads to many challenges for the control and modulation of the converter as well as for proper low-latency high-reliability communication. This paper investigates the tolerable asynchronism between phase-shifted carriers used in modulation from a wireless control point of view and proposes a control method along with communication protocol for wireless control. The functionality of the proposed method is validated by computer simulations in steady state.
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| 22. |
- Ciftci, Baris, et al.
(författare)
-
Simple Distributed Control for Modular Multilevel Converters
- 2019
-
Ingår i: 2019 21st European Conference on Power Electronics and Applications, EPE 2019 ECCE Europe. - Brussels : European Power Electronics and Drives Association. - 9789075815306
-
Konferensbidrag (refereegranskat)abstract
- The central control of MMC becomes demanding in computation power and communication bandwidth as the number of submodules increase. Distributed control methods can overcome these bottlenecks. In this paper, a simple distributed control method together with synchronization of modulation carriers in the submodules is presented. The proposal is implemented on a lab-scale MMC with asynchronous-serial communication on a star network between the central and local controllers. It is shown that the proposed control method works satisfactorily in the steady state. The method can be applied as is to MMCs with any number of submodules per arm.
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| 23. |
- Heinig, Stefanie, et al.
(författare)
-
Implications of Capacitor Voltage Imbalance on the Operation of the Semi-Full-Bridge Submodule
- 2019
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 34:10, s. 9520-9535
-
Tidskriftsartikel (refereegranskat)abstract
- Future meshed high-voltage direct current grids require modular multilevel converters with extended functionality. One of the most interesting new submodule topologies is the semi-full-bridge because it enables efficient handling of DC-side short circuits while having reduced power losses compared to an implementation with full-bridge submodules. However, the semi-full-bridge submodule requires the parallel connection of capacitors during normal operation which can cause a high redistribution current in case the voltages of the two submodule capacitors are not equal. The maximum voltage difference and resulting redistribution current have been studied analytically, by means of simulations and in a full-scale standalone submodule laboratory setup. The most critical parameter is the capacitance mismatch between the two capacitors. The experimental results from the full-scale prototype show that the redistribution current peaks at 500A if the voltage difference is 10V before paralleling and increases to 2500A if the difference is 40V. However, neglecting very unlikely cases, the maximum voltage difference predicted by simulations is not higher than 20-30V for the considered case. Among other measures, a balancing controller is proposed which reduces the voltage difference safely if a certain maximum value is surpassed. The operating principle of the controller is described in detail and verified experimentally on a down-scaled submodule within a modular multilevel converter prototype. It can be concluded that excessively high redistribution currents can be prevented. Consequently, they are no obstacle for using the semi-full-bridge submodule in future HVDC converters.
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| 24. |
- Heinig, Stefanie, et al.
(författare)
-
Reduction of Switching Frequency for the Semi-Full-Bridge Submodule Using Alternative Bypass States
- 2018
-
Ingår i: 2018 20TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'18 ECCE EUROPE). - : IEEE. - 9789075815283
-
Konferensbidrag (refereegranskat)abstract
- As regards modular multilevel converter submodules, a different number of switches may be involved in the transitions between voltage levels depending on the submodule type and choice of switching states. In this paper, an investigation of the average switching frequency associated with different choices of bypass states is performed for the semi-full-bridge submodule. Theoretical considerations and simulation results show that the average switching frequency per device can be halved by using the proposed alternative bypass state. Moreover, the switching losses can be reduced by up to 60%. Finally, a comparative study with the full-bridge submodule has been conducted.
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| 25. |
- Heuvelmans, Matthijs
(författare)
-
Cost-effective Cells for High-power Modular Multilevel Converters
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The modular multilevel converter (MMC) topology was introduced in 2003and has since been receiving considerable attention from industry and academia.Notable benefits compared to two- or three-level voltage source convertersare its scalability, low switching losses, low output filter requirementsand ease of adding redundancy combined with fail-safe operation. There area number of disadvantages, such as the use of large bus capacitors and complexityof control. However, with currently predominant switch technology forhigh power levels, which are bipolar silicon devices, the benefits outweigh thedisadvantages. The use of integrated gate commutated thyristors (IGCTs) inan MMC is an attractive option compared to using IGBTs due to their robustnessand low conduction losses. Switching losses are of lesser importance,but not negligible.The objectives of this work are to contribute to a reduction in equipmentcost and to a decrease power loss in HVDC and STATCOM installations.The approach to achieve those objectives is by using the auxiliary resonantcommutated pole topology in IGCT-based MMC. In case thyristors are usedas auxiliary switches, the total amount of needed hardware does not differsignificantly from a hard-switched solution which needs a di/dt reactor and asnubber. The reduced switching losses in the main switches (IGCTs) lead toan efficiency increase, but also to the possibility of using higher-voltage devicesthat would otherwise be impracticable. This in turn can lead to a reduction inhardware cost due to a lower number of cells and lower conduction losses. Inaddition, the improved switching conditions allow for an increase in turn-offcurrent capability. Practical aspects that are also treated in this work are theuse of snubber circuits for the auxiliary switch, and the behaviour under ashoot-through. The latter aspect is essential for practical use in high-powerMMCs. In this work a fault-tolerant soft-switching cell is presented, whichallows for a current limiting series inductance between the main switches andthe dc-bus capacitor without causing a problematic voltage overshoot.
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| 26. |
- Jacobs, Keijo, et al.
(författare)
-
Dissipation Loop for Shoot-Through Faults in HVDC Converter Cells
- 2018
-
Ingår i: 2018 INTERNATIONAL POWER ELECTRONICS CONFERENCE (IPEC-NIIGATA 2018 -ECCE ASIA). - : Institute of Electrical and Electronics Engineers (IEEE). - 9784886864055 ; , s. 3292-3298
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Konferensbidrag (refereegranskat)abstract
- Converter cells for HVDC applications store large amounts of energy. This energy might be dissipated in a very short time in case of a shoot-through fault. Measures to avoid shoot-through or handle the extreme currents during a fault and prevent damage from neighboring components are essential to ensure a continued operation of the converter. With future high-voltage silicon carbide semiconductors, cell voltages can be increased leading to higher stored energy per cell. In cells with thyristor-based semiconductors, e.g. IGCTs, a di/dt reactor may have to be employed. This paper presents a method to handle the dissipated energy during shoot-through which makes use of the inherently needed di/dt reactor. The majority of the stored energy in the cell can be dissipated in a dedicated discharge loop formed by the reactor and an antiparallel bypass thyristor. After diverting the fault current into the dissipation loop, there is no current through any other component of the cell.
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| 27. |
- Jacobs, Keijo, et al.
(författare)
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Low Loss Submodule Cluster for Modular Multilevel Converters Suitable for Implementation with SiC MOSFETs
- 2019
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Ingår i: Proceedings IEEE Energy Conversion Congress and Exposition 2019. - : IEEE. - 9781728103952 - 9781728103969
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Konferensbidrag (refereegranskat)abstract
- In this paper, a novel submodule cluster topologyfor modular multilevel converters is proposed. The cluster iscomposed of an arbitrary amount of submodule segments. Dependingon the amount of capacitors in the cluster, the converterconduction losses can be reduced significantly. The topologyenables electronic protection against explosion, thus, reducingthe requirements for submodule bypass equipment. Implicationsfor the converter operation and functionality are investigated anda wireless control scheme is proposed.
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| 28. |
- Jacobs, Keijo, et al.
(författare)
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MMC Converter Cells Employing Ultrahigh-Voltage SiC Bipolar Power Semiconductors
- 2017
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Ingår i: 2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE EUROPE). - : Institute of Electrical and Electronics Engineers (IEEE). - 9789075815276
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the benefits of using high-voltage converter cells for transmission applications. These cells employ ultrahigh-voltage SiC bipolar power semiconductors, which are optimized for low conduction losses. The Modular Multilevel Converter with half-bridge cells is used as a test case. The results indicate a reduction of converter volume and complexity, while maintaining low losses and harmonic performance.
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| 29. |
- Jahn, Ilka, et al.
(författare)
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A Proposal for Open-Source HVDC Control
- 2019
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Konferensbidrag (refereegranskat)abstract
- Future multiterminal high-voltage direct-current (HVDC) grids are considered an enabling technology to efficiently integrate large amounts of renewable energy into the existing grid. However, already in today’s existing point-to-point HVDC links, harmonic interaction issues and instabilities related to the controland protection system of the converters have been reported. The converter control software is usually black-boxed and problems are therefore solved in close cooperation with the HVDC vendor. This paper aims to provide a starting point for a discussion onan open-source HVDC control system. In particular, it covers the control design including technical and non-technical aspects. The open-source approach can be useful to solve current as wellas future control-related problems, both in point-to-point links as well as in multiterminal and multivendor HVDC grids.
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| 30. |
- Jahn, Ilka, et al.
(författare)
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Impact of measurement and communication aspects on protection of multi-terminal DC grids
- 2018
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Ingår i: The Journal of Engineering. - : Institution of Engineering and Technology. - 2051-3305.
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Tidskriftsartikel (refereegranskat)abstract
- The increased demand for renewable energy generation requires the higher flexibility of transmission systems. This requirement together with technical progress in high-voltage DC technology has resulted in the ambition to build large-scale multi-terminal DC grids. To achieve this goal, vendor interoperability is considered a key element. Standards exist for AC systems, but not for DC systems. This work discusses and evaluates the suitability of AC standards for DC systems. As a result, a different view on substation architecture is developed and two communication protocols are suggested for further investigation in this context.
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| 31. |
- Jahn, Ilka, et al.
(författare)
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Impact of Measurement and Communication on Protection of MTDC Grids
- 2018
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Konferensbidrag (refereegranskat)abstract
- The increased demand for renewable energy generation requires higher flexibility of transmission systems. This requirement together with technical progress in high-voltage direct-current (HVDC) technology have resulted in the ambition to build large-scale multi-terminal DC (MTDC) grids. To achieve this goal, vendor interoperability is considered a key element. Standards exist for AC systems,but not for DC systems. This work discusses and evaluates the suitability of AC standards for DC systems. As a result, a different view on substation architecture is developed and two communication protocols are suggested for further investigation in this context.
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| 32. |
- Jin, Lebing, et al.
(författare)
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Communication-Based Distributed Control of the Stacked Polyphase Bridges Converter
- 2018
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Ingår i: IEEE Transactions on Industrial Electronics. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0278-0046 .- 1557-9948. ; 65:2, s. 1011-1020
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Tidskriftsartikel (refereegranskat)abstract
- The stacked polyphase bridges converter has gained increasing interest in recent years due to its modular design and easy adaption to different power levels. The real-time control and dynamic data transmission of a stacked polyphase bridges converter consisting of a number of submodules are challenging tasks. For the reason that the distributed control architecture can maintain the benefit of modularity, such an approach dedicated for the stacked polyphase bridges converter is presented in this paper. Suitable communication techniques and synchronization techniques for the presented architecture are discussed. In addition, based on a dynamic model of the converter, the sensitiveness of the distributed control system to communication bandwidth and delay is studied on an experimental prototype.
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| 33. |
- Johannesson, Niclas, et al.
(författare)
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Contribution of travelling wave propagation time to the speed of optical link protections in multi-terminal high-voltage DC systems
- 2019
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Ingår i: IET Generation, Transmission & Distribution. - : Institution of Engineering and Technology. - 1751-8687 .- 1751-8695. ; 13:14, s. 3078-3085
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Tidskriftsartikel (refereegranskat)abstract
- During faults in multi-terminal high-voltage DC systems, the disturbance will quickly become evident throughout the entire system. If DC breakers are included in such systems, the entire fault clearing process needs to occur within a few milliseconds. Therefore, DC line protection schemes based on telecommunication have previously been discarded by some authors as their performance is constrained by the communication delay. However, telecommunication-based detection methods offer some very favourable features, one being that selectivity can be achieved without coordination of settings. In this study, several telecommunication-based protection schemes are evaluated with regards to their minimum possible detection time when considering telecommunication delay. It is shown that they perform best during faults located at the remote end of a line, i.e. fault locations that are difficult to reliably detect using single-ended methods. Therefore, it is reasonable that the most reliable protection system will consist of both single-ended and communication-based methods because they complement each other well. Furthermore, it is shown that the travelling wave differential protection offers the shortest theoretical detection time due to the wave propagation delay being included in the formulation.
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| 34. |
- Johannesson, Niclas, et al.
(författare)
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Estimation of travelling wave arrival time in longitudinal differential protections for multi-terminal HVDC systems
- 2018
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Ingår i: The Journal of Engineering. - : Institution of Engineering and Technology (IET). - 2051-3305. ; :15, s. 1007-1011
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Tidskriftsartikel (refereegranskat)abstract
- Multi-terminal high-voltage DC (HVDC) systems equipped with HVDC breakers require that detection and clearing of faults occur within a few milliseconds. Although detection without communication is generally preferred with regard to detection delay and simplicity, detection schemes relying on communication can enhance the overall performance due to their reliability. One such principle is the travelling wave differential protection that is based on the comparison of waves at both ends rather than solely on current. However, as with conventional differential protections, some kind of synchronisation must be applied to properly compensate for the time difference between samples obtained at different geographical locations. In this study, a synchronisation algorithm is presented that applies real-time signal processing to automatically obtain a proper compensation between the signals from both ends. The algorithm is examined by injection of data samples, generated from the simulation of an external fault in a PSCAD/EMTDC model. Additionally, the suitability for a real-time implementation is evaluated by execution time estimation using a simulated DSP. The algorithm is found to perform well, not only in identifying the compensation delay but also in terms of computational efficiency, thus allowing for real-time application.
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| 35. |
- Modeer, Tomas, 1979-, et al.
(författare)
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High-Voltage Tapped-Inductor Buck Converter Utilizing an Autonomous High-Side Switch
- 2015
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Ingår i: IEEE Transactions on Industrial Electronics. - : IEEE Press. - 0278-0046 .- 1557-9948. ; 62:5, s. 2868-2878
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Tidskriftsartikel (refereegranskat)abstract
- A high-voltage tapped-inductor buck converter utilizing a novel autonomous high-voltage valve is presented in this paper. Its application as auxiliary power supply for high-power cascaded-converter submodules is discussed, followed by a presentation of the most challenging problems in designing a low-power high-voltage step-down converter. The TI-buck converter topology is analyzed, which together with the novel autonomous high-voltage valve overcomes most of the problems. Analytical expressions describing the operation as well as circuit simulations are presented. Finally, an experimental evaluation of a 3-kV 70-W prototype converter utilizing the proposed autonomous high-voltage valve with series-connected super-junction MOSFETs is presented.
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| 36. |
- Sharifabadi, K., et al.
(författare)
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Design, control and application of modular multilevel converters for HVDC transmission systems
- 2016
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Design, Control and Application of Modular Multilevel Converters for HVDC Transmission Systems is a comprehensive guide to semiconductor technologies applicable for MMC design, component sizing control, modulation, and application of the MMC technology for HVDC transmission. Separated into three distinct parts, the first offers an overview of MMC technology, including information on converter component sizing, Control and Communication, Protection and Fault Management, and Generic Modelling and Simulation. The second covers the applications of MMC in offshore WPP, including planning, technical and economic requirements and optimization options, fault management, dynamic and transient stability. Finally, the third chapter explores the applications of MMC in HVDC transmission and Multi Terminal configurations, including Supergrids. Key features: Unique coverage of the offshore application and optimization of MMC-HVDC schemes for the export of offshore wind energy to the mainland. Comprehensive explanation of MMC application in HVDC and MTDC transmission technology. Detailed description of MMC components, control and modulation, different modeling approaches, converter dynamics under steady-state and fault contingencies including application and housing of MMC in HVDC schemes for onshore and offshore. Analysis of DC fault detection and protection technologies, system studies required for the integration of HVDC terminals to offshore wind power plants, and commissioning procedures for onshore and offshore HVDC terminals. A set of self-explanatory simulation models for HVDC test cases is available to download from the companion website. This book provides essential reading for graduate students and researchers, as well as field engineers and professionals who require an in-depth understanding of MMC technology.
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| 37. |
- Zhang, Hui, 1988-, et al.
(författare)
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Evaluation of Modular Integrated Electric Drive Concepts for Automotive Traction Applications
- 2017
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Ingår i: IEEE Transactions on Transportation Electrification. - : IEEE. - 2577-4212.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In order to achieve compactness and realize a certain level of fault tolerance in integrated motor drives, a number of integrated modular motor drive concepts have been proposed in recent years. In this paper, converter topology candidates suitable for an IMMD are considered with particular focus on the stacked polyphase bridges cconverter; the parallel-connected polyphase bridges converter, and the modular high frequency converter. A comparative evaluation of the studied topologies is presented and discussed in terms of machine design aspects, power losses, capacitor energy storage requirements, costs, and cell redundancy using the conventional two-level three-phase drive system as reference.
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| 38. |
- Ängquist, Lennart, et al.
(författare)
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A new dc breaker with reduced need for semiconductors
- 2016
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Ingår i: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE). - : IEEE.
-
Konferensbidrag (refereegranskat)abstract
- A renewed interest for dc breakers has evolved owing to the visions of connecting several HVDC links into a HVDC grid. Several breaker concepts have been presented and some also have been implemented and tested. A new approach is proposed in this paper. The fundamental principle is to take advantage of the fast recovery of the voltage withstand capability in a Vacuum Interrupter (VI) when the current is temporarily forced to zero using a low-voltage power electronic converter. The latter excites an oscillating current in a passive resonant circuit during the time interval needed to mechanically separate the contacts in the interrupter. The sum of the line current (to be interrupted) and the oscillating current passes through the vacuum interrupter and experiences zero-crossings when the amplitude of the oscillating current exceeds the line current. The most important benefit of the proposed concept is that a favorable cost can be achieved, because excitation of the oscillating current only requires a low output voltage (compared to the breaking voltage across the VI terminals) from the converter. The total voltage rating of the semiconductors in the latter therefore is only a fraction of that needed in a hybrid HVDC breaker and, additionally, they are not requested to turn off the main current but rather to commutate close to current zero-crossings. Experimental verification of the concept has been performed with current up to 1.6 kA against 1.2 kV.
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| 39. |
- Ängquist, Lennart, et al.
(författare)
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VARC - A Cost-Effective Ultrafast DC Circuit Breaker Concept
- 2018
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Ingår i: 2018 IEEE POWER & ENERGY SOCIETY GENERAL MEETING (PESGM). - : IEEE. - 9781538677032
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Konferensbidrag (refereegranskat)abstract
- A concept for a dc circuit-breaker is proposed. A vacuum interrupter is used together with a resonant circuit excited by a power electronic converter to create a zero-crossing in the interrupter current. A low amount of semiconductor devices is needed because they perform repeated switching operations during current excitation. Tests have been performed with a prototype interrupting 10 kA against 9 kV in 3 ms.
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