| 52461. |
- Mademlis, Georgios, 1992, et al.
(författare)
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Comparative Study of the Torque Ripple and Iron Losses of a Permanent Magnet Synchronous Generator Driven by Multilevel Converters
- 2018
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Ingår i: 2018 23rd International Conference on Electrical Machines (ICEM). - 2381-4802. - 9781538624777
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Konferensbidrag (refereegranskat)abstract
- This paper studies and analyzes the performance of permanent magnet synchronous generator (PMSG) drives with multilevel power converters used in medium voltage renewable power generation systems. The cases of electrical machine drives with 2-level back-to-back-connected voltage source converters as well as 3-and 5-level neutral-point-clamped converters are examined. The converters have been constructed with silicon-carbide (SiC) power switches. The comparison in the power converters efficiency and power quality is conducted by using simulation results obtained by the Matlab/Simulink and PLECS programs for several operating conditions. For the needs of the comparison, a medium voltage PMSG is designed and its efficiency and torque ripple are calculated by using the finite element software ANSYS Maxwell. Several simulation results are presented and discussed throughout the paper in order to demonstrate the improvements in the PMSG torque ripple and the iron loss reduction that can be achieved by using multilevel converters.
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| 52462. |
- Mademlis, Georgios, 1992, et al.
(författare)
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DC-DC Converter based on the Asymmetric Multistage Stacked Boost Architecture with Feed-Forward Control for Photovoltaic Plants
- 2016
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Ingår i: PCIM Europe 2016; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management. - 9783800741861 ; , s. 445-452
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Konferensbidrag (refereegranskat)abstract
- A new feed-forward control technique for a DC-DC step-up converter based on the asymmetric Multistage Stacked Boost Architecture (MSBA) is presented in this paper. The proposed closed loop control scheme can provide improved accuracy in the steady-state operation and high dynamic performance. The asymmetric MSBA converter is a single output high-voltage DC-DC step-up converter that comprises several in-series connected capacitors with active voltage balancing circuits. The converter can attain high voltage ratios and thus, it is a suitable solution for the high voltage transmission requirements of the large photovoltaic (PV) plants. Selective simulation and experimental results are presented in order to validate the effectiveness and the operational improvements of the proposed control system.
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| 52463. |
- Mademlis, Georgios, 1992, et al.
(författare)
-
DC Link Voltage Balancing Technique Utilizing Space Vector Control in SiC-based Five-Level Back-to-Back-Connected NPC Converters
- 2018
-
Ingår i: 2018 IEEE Energy Conversion Congress and Exposition (ECCE). - 2329-3748. - 9781479973125 - 9781479973118 ; , s. 3032-3037
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Konferensbidrag (refereegranskat)abstract
- This paper presents an improved voltage balancing algorithm of the dc-link capacitors in an electric drive with back-to-back connected five-level neutral-point-clamped (NPC) converters. A properly modified space-vector-pulse-width-modulation (SVPWM) algorithm is developed, which balances the capacitor voltages effectively by utilizing the redundant states of the space vector plane. The dc link voltage balancing is attained by the proper control of the NPC converters without requiring any additional hardware and, thus, the cost of the electric drive can be minimized. This paper presents the theoretical analysis of the proposed voltage balancing technique for all the operating conditions of the converters. A 50kW electric drive is simulated on Matlab/Simulink and modelled using PLECS in order to accurately calculate the losses of the converters. SiC power switches are used for the prototypes of the 5-level NPC converters. Selective experimental results are also shown.
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| 52464. |
- Mademlis, Georgios, 1992, et al.
(författare)
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Design of Maximum Power Point Tracking for Dynamic Power Response of Tidal Undersea Kite Systems
- 2020
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Ingår i: IEEE Transactions on Industry Applications. - 0093-9994 .- 1939-9367. ; 56:2, s. 2048-2060
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Tidskriftsartikel (refereegranskat)abstract
- The Tethered-Undersea-Kite (TUSK) represents a new electric power generation concept for harvesting energy from tidal currents, with higher power density compared to traditional static tidal turbines. However, the power and rotating speed of the turbine fluctuate periodically depending on the kite's motion in the sea creating an additional challenge for the speed control of the generator. The mathematical model of the system's power generation is developed. Two alternative Maximum-Power-Point-Tracking (MPPT) algorithms suitable for this application are designed. The electrical torque of the generator is controlled directly or a more accurate closed-loop speed controller is used. The turbine inertia creates an error between the optimal-reference power and the actual generated power. This error is evaluated experimentally for both MPPT-algorithms when fluctuating mechanical torque typical for the TUSK-system is applied on the generator. Experimental results on a 35kVA laboratory emulator are presented, where an accurate representation of the system dynamics and inertia are implemented.
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| 52465. |
- Mademlis, Georgios, 1992, et al.
(författare)
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Designing Thermally Uniform Heatsink with Rectangular Pins for High-Power Automotive SiC Inverters
- 2020
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Ingår i: IECON Proceedings (Industrial Electronics Conference). - 2162-4704 .- 2577-1647. ; 2020-October, s. 1317-1322
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Konferensbidrag (refereegranskat)abstract
- This paper presents the design of a high-performance liquid-cooled heatsink for three-phase automotive inverters that attains uniform thermal distribution at the surface of the three power modules. Power modules with SiC-MOSFETs are used in this study and a uniform thermal distribution on the heatsink guarantees equal thermal loading of the semiconductor devices. A comparative study of various cooling plate geometries is made and their effectiveness in meeting the design objectives of low sink-temperature and coolant pressure drop and the highest possible temperature uniformity along the surface of the plate is presented. Plates with straight and wavy fins are compared with designs accommodating rectangular pins and the advantages of each case is shown with the corresponding simulation results. Key design parameters of the cooling plate geometries are optimized with an iterative process, which is presented with selective simulation results of 3D Conjugate Heat Transfer computations for coolant flow rates up to 10~l/min. The final heatsink design accommodates multiple rectangular pins and attains temperature difference of less than 2oC among the three SiC power modules.
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| 52466. |
- Mademlis, Georgios, 1992, et al.
(författare)
-
Feed-Forward-based Control in a DC–DC Converter of Asymmetric Multistage-Stacked Boost Architecture
- 2016
-
Ingår i: IEEE Transactions on Power Electronics. - 0885-8993 .- 1941-0107. ; 32:2, s. 1507-1517
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Tidskriftsartikel (refereegranskat)abstract
- A new feed-forward control technique for a dc-dc step-up converter based on the asymmetric multistage stacked boost architecture (MSBA) is proposed. The developed feed-forward controller directly handles the load current and the perturbations that may be caused by the dynamic operation of the converter. Thus, there is no time delay for estimating the error in a control process, and therefore, both robust steady-state operation and high dynamic performance can be achieved. The asymmetric MSBA dc-dc converter is a single-output high-voltage topology that embodies several in-series active voltage-balancing circuits. Thus, there is a need for an improved balancing control method. This can be accomplished by replacing the conventional proportional-integral controllers with feed-forward type and therefore improved balancing between the stages can be attained, because the steady-state errors are suppressed and the dynamic response can be enhanced. A thorough theoretical analysis is conducted for verifying the stability of the suggested feed-forward control technique in an asymmetric MSBA converter, and selective simulation and experimental results are demonstrated in order to validate the effectiveness and feasibility of the proposed control scheme.
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| 52467. |
- Mademlis, Georgios, 1992, et al.
(författare)
-
Feed-Forward Control for Active Voltage Balancing in Electric Drives with Five-Level NPC Converters
- 2018
-
Ingår i: 2018 IEEE Energy Conversion Congress and Exposition (ECCE). - 2329-3748. - 9781479973125 - 9781479973118
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a feed-forward-based control system for actively balancing the dc link voltages of an electric drive with five-level neutral-point-clamped (NPC) converters. The dc link capacitor voltages are balanced through a bidirectional dc/dc converter. The space-vector-modulation technique of the NPC converters contributes also to the voltage balancing in some operating conditions. This paper presents a feed-forward-based control system for the dc/dc converter that offers robust performance with low steady state error between the dc link capacitor voltages. The control system consists of voltage and current controllers for regulating the dc link voltages and currents of back-to-back-connected three-phase five-level NPC converters. This paper also describes the methodology to estimate the currents at the dc side of five-level three-phase NPC converters, since measurements of the dc link currents are necessary for controlling the dc/dc converter. The structure of the proposed control technique is presented and a 50kW system is simulated on Matlab/Simulink and validated experimentally with a low scaled prototype system.
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| 52468. |
- Mademlis, Georgios, 1992, et al.
(författare)
-
Generator Speed Control and Experimental Verification of Tidal Undersea Kite Systems
- 2018
-
Ingår i: 2018 23rd International Conference on Electrical Machines (ICEM). - 2381-4802. - 9781538624777 ; , s. 1531-1537
-
Konferensbidrag (refereegranskat)abstract
- Tethered-UnderSea-Kites (TUSK) represent a new electric power generation concept for harvesting the energy of the tidal current. A TUSK system has the advantage of increasing the extracted power from the tidal flow compared to a traditional static tidal turbine of the same size. This paper deals with the modeling and control of a TUSK tidal generator in order to estimate the energy production of such a system. A model of the generator drive mounted on a TUSK is presented in this paper. The produced power is periodically variating depending on the kite's motion into the sea and a suitable Maximum-Power-Point-Tracking (MPPT) algorithm for controlling the generator speed has been developed in order to maximize the power production. The developed control strategy of the drive has been experimentally verified with a 35kVA laboratory emulator of the TUSK and experimental results of several power production profiles are shown.
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| 52469. |
- Mademlis, Georgios, 1992
(författare)
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Inverter Design for SiC-based Electric Drive Systems with Optimal Redundant States Control of Space Vector Modulation
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The need for inverters with ever increasing power density and efficiency has recently become the driving factor for research in various fields. Increasing the operating voltage of the whole drive system and utilizing newly developed SiC power switches can contribute towards this goal. Higher operating voltage allows the design of drives with lower current, which leads to lower copper losses in cables and machine, while SiC switches can drastically increase the inverter efficiency. Offshore renewable power generation, such as tidal power, is a typical application where the increase of operating voltage can be highly beneficial. The ongoing electrification of transportation calls also for high power electric powertrains with high power density, where SiC technology has key advantages. In the first part of the thesis, suitable control schemes for inverters in synchronous machine drive systems are derived. A properly designed Maximum Power Point Tracking algorithm for kite-based tidal power systems is presented. The speed and torque of this new tidal power generation system varies periodically and the inverter control needs to be able to handle this variable power profile. Experimental verification of the developed control is conducted on a 35 kVA laboratory emulator of the tidal power generation unit. Electric drives using multilevel inverters are studied afterwards. Multilevel inverters use multiple low-voltage-rated switches and can operate at higher voltage than standard two-level inverters. The Neutral Point Clamped (NPC) converter is a commonly used multilevel inverter topology for medium voltage machine drives. However, the voltage balancing of its dc-side capacitors and the complexity of its control are still issues that have not been effectively solved. A new method for the optimal utilization of the redundant states in Space Vector pulse-width-Modulation (SVM) is proposed in this thesis in order to control its dc-link voltages. Experimental verification on a 4-kV-rated prototype medium-voltage PMSM drive with 5-level NPC converters is conducted in order to validate the effectiveness of the proposed control technique. Low switching and conduction losses are typical characteristics of SiC switches that can be utilized to build inverters with high power density, due to the increased efficiency and smaller form-factor. Due to the above, SiC power modules have been particularly attractive for the automotive industry. The design approach of 2-level automotive inverters has been studied in this project. Moreover, a new design approach for the cooling system of automotive inverters has been developed in this thesis, which fine-tunes the inverter heatsink utilizing standard legislated test routines for electric vehicles. Multiple conjugate-heat-transfer (CHT) computation results showcase the iterative optimization procedure on a test-case 250 kW (450 A) automotive SiC inverter. Finally, the experimental testing of high power machine drives in order to verify the control and the hardware design is an important step of the development process. Thus, the performance of the prototype 450 A SiC 2-level inverter has been been experimentally validated in a power hardware-in-the-loop (P-HIL) set-up that emulates an automotive drive system. Several challenges have been addressed with respect to the accurate modelling of the motor and the control of the circulating power in the system. A new control technique utilizing the redundant states of the SVM has been developed for this set-up to effectively suppress the zero-sequence current to 3.3 % of the line current at rated power.
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| 52470. |
- Mademlis, Georgios, 1992
(författare)
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Medium Voltage Generation System with Five-level NPC Converters for Kite Tidal Power
- 2019
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Offshore power generation has emerged as a prominent source of energy and the installed capacity of new plants has been steadily increasing in recent years. Tidal power specifically is a promising renewable energy source which has not been highly exploited yet, despite its distinctive advantages of being predictable and independent of weather conditions. The main objective of this Licentiate thesis is to analyze and propose solutions for two common problems in offshore power production, which are the power variations due to the non-steady speed profile of the water speed flowing through the turbine and the efficient transportation of the produced power to the shore. The tidal power application utilized in this thesis is the subsea kite, which is a recently developed tidal energy conversion technology that can increase the generated power compared to a traditional static tidal turbine. A turbine is mounted on a submerged kite and the kite moves inside the sea following a predefined trajectory and generating electric power from the tidal currents. The speed and torque of the turbine varies periodically due to the periodic movement of the kite in the sea and, therefore, the control of the generator needs to be able to handle this variable generated power. The kite studied in this thesis has rated active power of 500 kW. In the first part of the thesis, the power generation system of the subsea kite is modelled and the profile of the generated power is extracted given a specific tidal current and turbine geometry. The control of the power converters is described and tested for the specific profile of the generated power. The speed of the generator is controlled by a properly designed Maximum Power Point Tracking algorithm, which ensures that the generator extracts the maximum power from the tidal stream. Experimental verification of the model of this innovative system is also conducted on a laboratory 35 kVA emulator of the tidal power generator. The second part of the thesis deals with the design of a medium voltage generator drive. The use of medium voltage in the power generation system is highly advantageous for the tidal kite application, since it can reduce the current flowing through the undersea cables connecting the tidal plant to the local grid. Therefore, the size of the cables can be reduced. The drive proposed here uses two 5-level Neutral Point Clamped (NPC) converters connected back-to-back. The 5-level NPC converters can operate with high voltage, while using multiple low-voltagerated power switches. Contrarily, the typical 2-Level converters have limited voltage capability, since they would require more expensive high-voltage-rated power switches. The increased operating voltage of the power conversion system results to lower current and losses in the cables. Another advantage of the NPC converter is the low harmonics at the ac side, which reduces the requirements for passive grid filters. However, the voltage balancing of the dc-link capacitors in this converter topology is a challenge which has not been effectively solved in previous studies. Therefore, a novel voltage balancing strategy is proposed here that uses advanced Space-Vector-Modulation techniques and hardware-based voltage balancing schemes with reduced number of components and lower power losses. Finally, a laboratory prototype of the NPC-converter-based power conversion system is developed with rated power 50 kVA. SiC MOSFETs are used on the converters to further increase the system’s efficiency and voltage capability. This thesis presents the model, control and laboratory emulator of a kite-based tidal power generator. The experimental set-up can be utilized for conducting research on other renewable sources, such as wind power, that have similar performance. Also, the developed multilevel drive is suitable for various applications where medium voltage grid-connected drives are used and particularly in distributed renewable power generation.
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