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1.	Zhang, Yafan, et al. (författare) Thermal evaluation of a liquid/air cooled integrated power inverter for hybrid vehicle applications 2013 Ingår i: 2013 14th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, EuroSimE 2013. - New York : IEEE. - 9781467361385 - 9781467361378 ; , s. 6529944- Konferensbidrag (refereegranskat)abstract A thermal design of an integrated double-side cooled SiC 50kW-1200V-200A power inverter for hybrid electric vehicle applications has been proposed to enable cooling in two different automotive operating environments: under-hood and controlled temperature environment of passenger compartment. The power inverter is integrated with air/liquid cooled cold plates equipped with finned channels. Concept evaluation and CFD model calibration have been performed on a simplified thermal prototype. Computational experiments on the detailed model of the inverter, including packaging materials, have been performed for automotive industry defined application scenarios, including two extreme and one typical driving cycles. For the studied application scenarios the case temperature of the SiC transistors and diodes have been found to be below 210°C. The maximum steady-state temperature of the DC-link capacitor has been below 127 °C for the worst-case scenario including liquid cooling, and up to 140 °C for the worst-case scenario with air-cooling.
2.	Ahmed, Noman, et al. (författare) HVDC SuperGrids with modular multilevel converters - The power transmission backbone of the future 2012 Ingår i: International Multi-Conference on Systems, Signals and Devices, SSD 2012. - : IEEE. - 9781467315906 ; , s. 6198119- Konferensbidrag (refereegranskat)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.
3.	Ahmed, Noman, et al. (författare) Prospects and challenges of future HVDC SuperGrids with modular multilevel converters 2011 Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011). - 9781612841670 - 9789075815153 Konferensbidrag (refereegranskat)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 the future HVDC SuperGrids. Different topologies for a SuperGrid and the possibility to use modular multilevel converters (M2Cs) are presented. A comprehensive overview of different sub-module implementations of M2C is given. An overview of short circuit behaviour of the M2C is also given, as well as a discussion on the choice between cables or overhead lines and DC-side resonance issues.
4.	Haider, Arif, et al. (författare) Open-loop approach for control of multi-terminal DC systems based on modular multilevel converters 2011 Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011). - 9781612841670 - 9789075815153 Konferensbidrag (refereegranskat)abstract In this paper a multi-terminal direct current (MTDC) system with modular multilevel converters (M2Cs) is suggested. An open loop control method is used for the control of the converters. Each converter is modeled with 36 sub-modules per arm with a total of 216 sub-modules consisting of half bridges. Power-synchronization control is used instead of a phase-locked loop (PLL) for synchronization. Thus, the short circuit capacities of the ac systems are no longer limiting factors and the instability caused by the PLL in weak ac systems is avoided [10]. A direct voltage controller is implemented with power-synchronization control as an inner loop in one station. Several scenarios are analyzed to demonstrate control flexibility and ride-through capability for grid transients. By means of analytical calculations and time simulations in PSCAD/EMTDC, the validity of the proposed MTDC system is confirmed.
5.	Harnefors, Lennart, et al. (författare) Dynamic modeling of modular multilevel converters 2011 Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011). - 9781612841670 - 9789075815153 Konferensbidrag (refereegranskat)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. A selection of the so-called insertion indices, which compensates for the sum-capacitor-voltage ripples, is considered. The system which results for this selection is analyzed, and is shown to be asymptotically stable. Finally, explicit formulas for the steady-state sum-capacitor-voltage ripples are derived.
6.	Ilves, Kalle, et al. (författare) A new modulation method for the modular multilevel converter allowing fundamental switching frequency 2011 Ingår i: IEEE 8th International Conference on Power Electronics and ECCE Asia (ICPE & ECCE), 2011. - : IEEE. - 9781612849560 ; , s. 991-998 Konferensbidrag (refereegranskat)abstract This paper presents a new modulation method for the modular multilevel converter. The proposed method is based on a fixed pulse pattern where harmonic elimination methods can be applied. Modulation methods with harmonic elimination based on calculated pulse patterns have been presented for other multilevel topologies. However, similar modulation schemes have not yet been presented for the modular multilevel topology. In the proposed modulation method, the pulse pattern is chosen in such a way that the stored energy in each submodule remains stable. It is shown that this can be done at the fundamental switching frequency without measuring the capacitor voltages or using any other form of feedback control. Such a modulation scheme has not been presented before. The theoretical results are verified by both simulations and experimental results. The simulation results show successful operation at the fundamental switching frequency with a larger number of submodules. When a smaller number of submodules are used, harmonic elimination methods may be applied. This is verified experimentally on a converter with eight submodules per phase leg. The experimental results verify that stable operation can be maintained at the fundamental switching frequency while successfully eliminating the fifth harmonic in the ac-side voltage.
7.	Ilves, Kalle, et al. (författare) Analysis of arm current harmonics in modular multilevel converters with main-circuit filters 2012 Ingår i: International Multi-Conference on Systems, Signals and Devices, SSD 2012 - Summary Proceedings. - : IEEE. - 9781467315906 Konferensbidrag (refereegranskat)abstract In a modular multilevel converter the circulating current that flows through each phase leg can affect the performance and efficiency of the converter. If measures are not taken to control the circulating current, it will inevitably contain a second-order harmonic. There are various solutions for eliminating this second-order harmonic. One of the proposed solutions includes a main-circuit filter that is tuned to block the second-order harmonic in the circulating current. This paper presents an analytical relation between the ac-side current and the higher-order harmonics in the circulating current when such a filter is used. It is found that when third-order harmonic injection is used, a large fourth-order harmonic component may appear in the circulating current. This is verified by simulating a 32-MVA converter designed for grid connected applications. The simulation results support the conclusion that it is essential to take this effect into consideration when designing the main-circuit filter.
8.	Ilves, Kalle, et al. (författare) Controlling the ac-side voltage waveform in a modular multilevel converter with low energy-storage capability 2011 Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011). - 9781612841670 - 9789075815153 ; , s. 1-8 Konferensbidrag (refereegranskat)abstract During nominal operation of a modular multilevel converter the stored energy in the submodule capacitors will vary with time. If the energy storage capability of the capacitors is relatively small compared to the energy variations, this will give large variations in the capacitor voltages. These voltage variations will distort the ac-side voltage waveform and induce harmonic components in the current that is circulating between the dc terminals. The adverse effects on the ac-side voltage can be compensated for by identifying the factors that cause the distortion. It is shown that the compensation can be done by means of feed forward control while maintaining stable operating conditions and thus eliminating the need of additional stabilizing controllers. It is also shown that the voltage controller can be combined with a circulating current controller that removes the harmonics in the current that is circulating between the dc terminals. The functionality of the proposed controller is verified by both simulations and experimental results from a 10 kVA laboratory prototype. The simulations illustrate how the proposed controller successfully removes the distortion from the ac-side voltage waveform. The experimental results demonstrate stable operation during a step transient when the output power is increased by 125%.
9.	Ilves, Kalle, et al. (författare) Steady-State Analysis of Interaction Between Harmonic Components of Arm and Line Quantities of Modular Multilevel Converters 2012 Ingår i: IEEE transactions on power electronics. - IEEE. - 0885-8993 .- 1941-0107. ; 27:1, s. 57-68 Tidskriftsartikel (refereegranskat)abstract The fundamental frequency component in the arm currents of a modular multilevel converter is a necessity for the operation of the converter, as is the connection and bypassing of the submodules. Inevitably, this will cause alternating components in the capacitor voltages. This paper investigates how the arm currents and capacitor voltages interact when the submodules are connected and bypassed in a sinusoidal manner. Equations that describe the circulating current that is caused by the variations in the total inserted voltage are derived. Resonant frequencies are identified and the resonant behaviour is verified by experimental results. It is also found that the effective values of the arm resistance and submodule capacitances can be extracted from the measurements by least square fitting of the analytical expressions to the measured values. Finally, the analytical expression for the arm currents is verified by experimental results.
10.	Kostov, Konstantin, et al. (författare) Conducted EMI from SiC BJT boost converter and its dependence on the output voltage, current, and heatsink connection 2013 Ingår i: 2013 IEEE ECCE Asia Downunder - 5th IEEE Annual International Energy Conversion Congress and Exhibition, IEEE ECCE Asia 2013. - : IEEE. - 9781479904839 ; , s. 1125-1130 Konferensbidrag (refereegranskat)abstract In comparison to their Silicon (Si) counterparts, the Silicon Carbide (SiC) power transistors have lower on-state resistance and higher switching speed, power and temperature ratings. These advantages make it possible to build smaller, lighter and more efficient power converters. Unfortunately, all these benefits come at the price of higher conducted and radiated electromagnetic interference (EMI). This paper investigates the conducted disturbances from a 6 kW boost converter with SiC bipolar junction transistors (BJTs). The results show that the conducted emissions at the input of the converter are approximately proportional to the output voltage, but almost independent on the load current. The effect of the heatsink on the conducted EMI was studied as well. It was found that using separate heatsinks for the diode and the BJT did not affect the level of conducted emissions significantly, but the way of connecting the heatsink does. A floating heatsink is bad from an EMI point of view, and in many cases it may not be allowed for safety reasons. When the heatsink is grounded, alone or together with the negative terminal, the common-mode noise increases the EMI measured at the positive line and decreases the EMI on the negative line. However, this appears only in the lower frequency range. At higher frequencies, connecting the heatsink in any way is better than letting it float. Therefore, the best option is to connect the heatsink to the negative line of the boost converter, and if grounding is required, it may be grounded as well. This may not be possible in systems where the negative voltage bus is at non-zero potential.
11.	Lim, Jang-Kwon, et al. (författare) Comparison of total losses of 1.2 kV SiC JFET and BJT in DC-DC converter including gate driver 2011 Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 679/680, s. 649-652 Tidskriftsartikel (refereegranskat)abstract The 1.2 kV SiC JFET and BJT devices have been investigated and compared with respect to total losses including the gate driver losses in a DC-DC converter configuration. The buried grid, Normally-on JFET devices with threshold voltage of -50 V and -10V are compared to BJT devices with ideal semiconductor and passivating insulator interface and an interface with surface recombination velocity of 4.5·104 cm/s yielding agreement to the reported experimental current gain values. The conduction losses of both types of devices are independent of the switching frequency while the switching losses are proportional to the switching frequency. The driver losses are proportional to the switching frequency in the JFET case but to a large extent independent of the switching frequency in the BJT case. The passivation of the emitter junction modeled here by surface recombination velocity has a significant impact on conduction losses and gate driver losses in the investigated BJT devices.
12.	Lim, Jang-Kwon, et al. (författare) Design and gate drive considerations for epitaxial 1.2 kV buried grid N-on and N-off JFETs for operation at 250°C 2010 Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2009, PTS 1 AND 2. - STAFA-ZURICH : TRANS TECH PUBLICATIONS LTD. ; , s. 961-964 Konferensbidrag (refereegranskat)abstract The main problem when the conventional PSpice JFET model is used to simulate a vertical short-channel buried-grid JFET is caused by the constant values of Threshold Voltage (VTO) and Transconductance (BETA). This paper presents a new model for the vertical short-channel buried-grid 1200V JFET, where both VTO and BETA vary with respect to the Drain-Source voltage. Simulation data from Medici have been analyzed in order to extract the analytical equations for VTO and BETA. Also other PSpice parameters are extracted from these data. The proposed circuit model has been simulated in Matlab by optimizing the same algorithm that PSpice uses. A variety of results are shown and discussed in this paper.
13.	Lim, Jang-Kwon, et al. (författare) Evaluation of buried grid JBS diodes 2014 Ingår i: 15th International Conference on Silicon Carbide and Related Materials, ICSCRM 2013. - : Trans Tech Publications Inc.. - 9783038350101 ; , s. 804-807 Konferensbidrag (refereegranskat)abstract The 4H-SiC Schottky barrier diodes for high temperature operation over 200 °C have been developed using buried grids formed by implantation. Compared to a conventional JBS-type SBD with surface grid (SG), JBS-type SBD with buried grid (BG) has significantly reduced leakage current at reverse bias due to a better field shielding of the Schottky contact. By introducing the BG technology, the 1.7 kV diodes with an anode area 0.0024 cm2 (1 A) and 0.024 cm2 (10 A) were successfully fabricated, encapsulated in TO220 packages, and electrically evaluated. Two types of buried grid arrangement with different grid spacing dimensions were investigated. The measured IV characteristics were compared with simulation. The best fit was obtained with an active area of approximately 60% and 70% of the anode area in large and small devices, respectively. The measured values of the device capacitances were 1000 pF in large devices and 100 pF in small devices at zero bias. The capacitance values are proportional to the device area. The recovery behavior of big devices was measured in a double pulse tester and simulated. The recovery charge, Qc, was 18 nC and 24 nC in simulation and measurement, respectively. The fabricated BG JBS-type SBDs have a smaller maximum reverse recovery current compared to the commercial devices. No influence of the different grid spacing on the recovery charge was observed.
14.	Modéer, Tomas, 1979-, et al. (författare) Design and evaluation of tapped inductors for high-voltage auxiliary power supplies for modular multilevel converters 2012 Ingår i: 15th International Power Electronics and Motion Control Conference and Exposition, EPE-PEMC 2012 ECCE Europe. - : IEEE. - 9781467319713 ; , s. DS1b.231-DS1b.235 Konferensbidrag (refereegranskat)abstract Tapped-inductor buck converters can provide large step-down ratios at high efficiency and are well suited in auxiliary power supplies for modular multilevel converter cells supplying gate drive units etc. In this paper the design and testing of three low-leakage tapped inductors for use in a 3kV, 100W buck converter is described.
15.	Modéer, Tomas, 1979-, et al. (författare) High-voltage tapped-inductor buck converter auxiliary power supply for cascaded converter submodules 2012 Ingår i: 2012 IEEE Energy Conversion Congress and Exposition, ECCE 2012. - : IEEE. - 9781467308014 ; , s. 19-25 Konferensbidrag (refereegranskat)abstract This paper firstly presents a discussion of the requirements for an auxiliary power supply for high-power modular multilevel converter submodules. Next, some of the most challenging problems in designing a low power high voltage step-down converter are presented. Further, a suitable topology, the tapped-inductor buck converter, that overcomes most of the problems is analyzed. Both analytical expressions describing the operation and circuit simulations are presented. Finally, an experimental evaluation of a 3 kV, 100W prototype converter utilizing an autonomous high-voltage switch is presented.
16.	Modeer, Tomas, 1979-, et al. (författare) Implementation and testing of high-power IGCT-based cascaded-converter cells 2014 Ingår i: Proc. Energy Conversion Congress and Exposition (ECCE), 2014 IEEE. - : IEEE. ; , s. 5355-5359 Konferensbidrag (refereegranskat)abstract This paper presents the design and implementation of cascaded-converters cells based on integrated gate-commutated thyristor (IGCT) half-bridges. The cell design is presented together with a discussion of means to supply gate drive power and as well as the cooling of the cell components. Also, the operation of the cells in a high-power resonant test circuit is presented.
17.	Modéer, Tomas, et al. (författare) Loss comparison of different sub-module implementations for modular multilevel converters in HVDC applications 2011 Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011). - 9781612841670 - 9789075815153 Konferensbidrag (refereegranskat)abstract This paper presents a loss calculation and comparison between different submodule topologies and semiconductor choices for a Modular Multilevel Converter in a 1.1GW, ±320kV HVDC application.
18.	Modéer, Tomas, 1979-, et al. (författare) Loss comparison of different sub-module implementations for modular multilevel converters in HVDC applications 2012 Ingår i: EPE Journal. - : European Power Electronics and Drives Association. - 0939-8368 .- 2376-9319. ; 22:3, s. 32-38 Tidskriftsartikel (refereegranskat)abstract This paper presents a loss calculation and comparison between different submodule topologies and semiconductor choices for a Modular Multilevel Converter in a 1.1 GW, ± 320 kV HVDC application. Accordingly, a detailed analysis of the losses for three different M2C implementations using both insulated gate bipolar transistors (IGBTs) and integrated gatecommutated thyristors (IGCTs) is presented. The losses for six different submodule realizations are shown in a loss breakdown in Fig. 7. It shows that the very low conduction loss of the IGCT is to some degree offset by higher switching losses and extra turn-on snubber losses but that the IGCT implementations provide significantly lower losses than their IGBT counterparts. The loss break-down also shows that clamp-double submodules and full-bridge submodules suffer from approximately 25% and 50% additional losses respectively as compared to the half-bridge case. An experimental verification of the loss calculations has been performed using a down-scaled M2C prototype. The results show a very good agreement between calculations and measured losses.
19.	Modeer, Tomas, 1979-, et al. (författare) Resonant Test Circuit for High-Power Cascaded Converter Submodules 2013 Ingår i: Proc. European Conference on Power Electronics and Applications (EPE), 2013.. - : IEEE. Konferensbidrag (refereegranskat)abstract This paper presents a test circuit and methodology suitable for testing high-power half-bridge submodules such as would be used in cascaded converters for high-voltage dc converters. The circuit utilizes a series resonant tank and two half-bridge submodules with voltage and impedance cancellation in order to minimize hardware requirements.
20.	Nee, Hans-Peter, 1963-, et al. (författare) High-Efficiency Power Conversion Using Silicon Carbide Power Electronics 2013 Ingår i: Proc. of International Conference on silicon carbide and related materials (ICSCRM) 2013, Miyazaki, Japan, Sept. 29–Oct. 4, 2013. - : Trans Tech Publications Inc.. - 9783038350101 ; 778-780 Konferensbidrag (refereegranskat)abstract The message of this paper is that the silicon carbide power transistors of today are good enough to design converters with efficiencies and switching speeds beyond comparison with corresponding technology in silicon. This is the time to act. Only in the highest power range the devices are missing. Another important step towards high powers is to find new solutions for multi-chip circuit designs that are adapted to the high possible switching speeds of unipolar silicon carbide power transistors.
21.	Nee, Hans-Peter, 1963-, et al. (författare) Multi-chip circuit designs for silicon carbide power electronics 2014 Konferensbidrag (refereegranskat)abstract As the chip sizes of commercially available silicon carbide power transistors will remain smaller than for silicon counterpartsin the next five to ten years, multi-chip circuit designs will be necessary in order to reach power levels exceeding10 kW. In the present paper, therefore, experiences from parallel connected discrete devices, multi-chip modules,and parallel-connected multi-chip modules are presented. It is concluded that new multi-chip circuit designs are necessaryif the high switching speeds of silicon carbide power transistors should be exploited. In the opinion of the authors,each chip must be contacted by means of individual current paths, and internal bus bars conducting the whole current ofthe module must be avoided.
22.	Peftitsis, Dimosthenis, et al. (författare) Challenges regarding parallel-connection of SiC JFETs 2011 Ingår i: IEEE 8th International Conference on Power Electronics and ECCE Asia (ICPE & ECCE), 2011. - 9781612849560 ; , s. 1095-1101 Konferensbidrag (refereegranskat)abstract Considering the present development of the available Silicon Carbide switches, their current ratings are so low that they cannot be used for high-power converters. It is therefore necessary to connect several switches in parallel in order to obtain sufficient current ratings. An investigation of parallel-connected normally-on Silicon Carbide Junction Field Effect Transistors is presented in this paper. The parameters that play the most important role for the parallel connection are the pinch-off and the gate-source breakdown voltages. The temperature dependency of those two voltages is analyzed based on the pnp structure of the device. If the spread in these parameters is sufficiently large there might be no possibility for a stable off-state operation of a pair of transistors without forcing one of the gate voltages to exceed the breakdown voltage, especially at high temperatures. A solution to this problem is given. The switching performance of two pairs of parallel-connected devices is compared with respect to their pinch-off voltages, and it is found that differences of approximately 25% in switching losses could result from a difference in the pinch-off voltage of 0.5 V.
23.	Peftitsis, Dimosthenis, 1985-, et al. (författare) Design Considerations for a Self-Powered Gate Driver for Normally-ON SiC Junction Field-Effect Transistors 2013 Ingår i: 2013 IEEE ECCE Asia Downunder - 5th IEEE Annual International Energy Conversion Congress and Exhibition, IEEE ECCE Asia 2013. - : IEEE conference proceedings. - 9781479904839 ; , s. 251-257 Konferensbidrag (refereegranskat)abstract The very low on-state resistance, the voltagecontrolledgate, and the relative simplicity of fabrication of thenormally-ON silicon carbide junction field effect transistor makethis device the most important player among all state-of-theartsilicon carbide transistors. However, the normally-ON naturecounts as the main factor which keeps this device far frombeing considered as an alternative to the silicon insulated-gatebipolar transistor. A self-powered gate driver without externalpower supply for normally-ON silicon carbide junction field effecttransistors is presented in this paper. The proposed circuit isable to handle the shoot-through current when the devices aresubjected to the dc-link voltage by utilizing the energy associatedwith this current. On the other hand it supplies the necessarynegative gate-source voltage during the steady-state operation. Adetailed description of the operating states of the proposed circuitalong with various design considerations are presented. Fromexperiments which were performed in a half-bridge converter, itis shown that the shoot-through current can be turned off withinapproximately 15 s. Moreover, it is shown that the proposedgate driver can properly switch the devices.
24.	Peftitsis, Dimosthenis, et al. (författare) Experimental comparison of dc-dc boost converters with SiC JFETs and SiC bipolar transistors 2011 Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011). - 9781612841670 - 9789075815153 Konferensbidrag (refereegranskat)abstract An experimental performance comparison between SiC JFET and SiC BJT switches which are used as the main switch for a 2 kW dc/dc converter is presented. In order to perform a fair comparison and due to the different chip areas of these two SiC devices, they both operate under the same on-state losses. Moreover, the switching speeds of the gate and base drivers are approximately equal. It is experimentally shown that the SiC BJT is switching slightly faster than the SiC JFET under the same circuit conditions, while the driver loss for the SiC BJT is higher than for the JFET, especially at relatively low switching frequencies. Various experimental results dealing with the switching performance of the SiC devices and the power losses at different switching frequencies are presented. It is found that the BJT converter has a higher efficiency (99.0% measured at 50 kHz) that the JFET converter.
25.	Peftitsis, Dimosthenis, 1985-, et al. (författare) Experimental comparison of different gate-driver configurations for parallel-connection of normally-on SiC JFETs 2012 Ingår i: Conference Proceedings - 2012 IEEE 7th International Power Electronics and Motion Control Conference - ECCE Asia, IPEMC 2012. - : IEEE conference proceedings. - 9781457720864 ; , s. 16-22, s. 16-22 Konferensbidrag (refereegranskat)abstract Due to the low current ratings of the currently available silicon carbide (SiC) switches they cannot be employed in high-power converters. Thus, it is necessary to parallel-connect several switches in order to reach higher current ratings. This paper presents an investigation of parallel-connected normally-on SiC junction field effect transistors. There are four crucial parameters affecting the effectiveness of the parallel-connected switches. However, the pinch-off voltage and the reverse breakdown voltage of the gates seem to be the most important parameters which affect the switching performance of the devices. In particular, the spread in these two parameters might affect the stable off-state operation of the switches. The switching performance and the switching losses of a pair of parallel-connected devices having different reverse breakdown voltages of the gates is investigated by employing three different gate-driver configurations. It is experimentally shown that using a single gate-driver circuit the switching performance of the parallel-connected devices is almost identical, while the total switching losses are lower compared to the other two configurations.
26.	Peftitsis, Dimosthenis, et al. (författare) High-power modular multilevel converters with SiC JFETs 2010 Ingår i: 2010 IEEE Energy Conversion Congress and Exposition (ECCE). - : IEEE. - 9781424452866 ; , s. 2148-2155 Konferensbidrag (refereegranskat)abstract This paper studies the possibility of building a Modular Multilevel Converter (M2C) using Silicon Carbide (SiC) switches. The main focus is on a theoretical investigation of the conduction losses of such a converter and a comparison to a corresponding converter with silicon insulated gate bipolar transistors. Both SiC BJTs and JFETs are considered and compared in order to choose the most suitable technology. One of the sub-modules of a down-scaled 10 kVA prototype M2C is replaced with a sub-module with SiC JFETs without anti-parallel diodes. It is shown that diode-less operation is possible with the JFETs conducting in the negative direction, leaving the possibility to use the body diode during the switching transients. Experimental waveforms for the SiC sub-module verify the feasibility during normal steady-state operation. The loss estimation shows that a 300 MW M2C for high-voltage direct current transmission would potentially have an efficiency of approximately 99,8 % if equipped with future 3.3 kV 1.2 kA SiC JFETs.
27.	Peftitsis, Dimosthenis, 1985-, et al. (författare) High-Power Modular Multilevel Converters With SiC JFETs 2012 Ingår i: IEEE transactions on power electronics. - : IEEE Press. - 0885-8993 .- 1941-0107. ; 27:1, s. 28-36 Tidskriftsartikel (refereegranskat)abstract This paper studies the possibility of building a modular multilevel converter (M2C) using silicon carbide (SiC) switches. The main focus is on a theoretical investigation of the conduction losses of such a converter and a comparison to a corresponding converter with silicon-insulated gate bipolar transistors. Both SiC BJTs and JFETs are considered and compared in order to choose the most suitable technology. One of the submodules of a down-scaled 3 kVA prototype M2C is replaced with a submodule with SiC JFETs without antiparallel diodes. It is shown that the diode-less operation is possible with the JFETs conducting in the negative direction, leaving the possibility to use the body diode during the switching transients. Experimental waveforms for the SiC submodule verify the feasibility during normal steady-state operation. The loss estimation shows that a 300 MW M2C for high-voltage direct current transmission would potentially have an efficiency of approximately 99.8% if equipped with future 3.3 kV 1.2 kA SiC JFETs.
28.	Rabkowski, Jacek, 1975-, et al. (författare) A 6kW, 200kHz boost converter with parallel-connected SiC bipolar transistors 2013 Ingår i: 2013 Twenty-Eighth Annual IEEE Applied Power Electronics Conference And Exposition (APEC 2013). - : IEEE Press. - 9781467343534 ; , s. 1991-1998 Konferensbidrag (refereegranskat)abstract This paper describes issues related to design,construction and experimental verification of a 6 kW, 200 kHzboost converter (300 V/600 V) built with four parallel-connectedSiC bipolar transistors. The main focus is on parallel-connectionof the SiC BJTs: crucial device parameters and influence of theparasitics are discussed. A special solution for the base-driveunit, based on the dual-source driver concept, is also presentedin this paper. Experimental verification of the boost converterwith special attention to power loss measurement and thermalperformance of the parallel-connected transistors is also shown.The peak efficiency measured at nominal conditions wasapproximately 98.5% where the base-drive unit causes around 10% of the total losses.
29.	Rabkowski, Jacek, 1975-, et al. (författare) A Simple High-Performance Low-Loss Current-Source Driver for SiC Bipolar Transistors 2012 Ingår i: 7th International Power Electronics and Motion Control Conference (IPEMC), 2012. - : IEEE conference proceedings. - 9781457720857 ; , s. 222-228 Konferensbidrag (refereegranskat)abstract The paper proposes a novel topology of a simple base drive unit for silicon carbide bipolar junction transistors (BJTs) based on the current-source principle. Energy stored in a small, air-cored inductor is employed to generate a current peak forcing the BJT to turn-on (10–20ns) very rapidly. The driver enables very high switching performance and very low switching losses of the driven BJT. Both the current source and the unit delivering the steady-state current to the base are supplied from the same low-voltage source in order to limit power consumption. Operation principles as well as selected design issues are discussed in the paper and illustrated by experiments. The 1200V/6A SiC BJT driven by the proposed circuit shows a very fast switching speed.
30.	Rabkowski, Jacek, 1975-, et al. (författare) Design Steps Toward a 40-kVA SiC JFET Inverter With Natural-Convection Cooling and an Efficiency Exceeding 99.5% 2013 Ingår i: IEEE transactions on industry applications. - : IEEE Press. - 0093-9994 .- 1939-9367. ; 49:4, s. 1589-1598 Tidskriftsartikel (refereegranskat)abstract This paper describes the concept, design, construction, and experimental investigation of a 40-kVA inverter with silicon carbide junction field-effect transistors (JFETs). The inverter was designed to reach an efficiency exceeding 99.5%. The size of the heat sink is significantly reduced in comparison to silicon insulated-gate bipolar transistor designs, and the high efficiency makes it possible to use free-convection cooling. This could potentially increase reliability compared with solutions with fans. A very low conduction loss has been achieved by parallel connecting ten 85-m Omega normally-ON JFETs in each switch position. A special gate-drive solution was applied, forcing the transistors to switch very fast (approximately 10 kV/mu s), resulting in very low switching losses. As output power is almost equal to input power, special effort was done to precisely determine the amount of semiconductor power losses via comparative thermal measurements. A detailed analysis of the measurements shows that the efficiency of the inverter is close to 99.7% at 40 kVA.
31.	Rabkowski, Jacek, et al. (författare) Design steps towards a 40-kVA SiC inverter with an efficiency exceeding 99.5% 2012 Ingår i: Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC. - : IEEE. - 9781457712159 ; , s. 1536-1543 Konferensbidrag (refereegranskat)abstract This paper describes the concept, the design, the construction, and experimental investigation of a 40 kVA inverter with Silicon Carbide Junction Field Effect Transistors. The inverter was designed to have an efficiency exceeding 99.5%. Due to the low losses free convection cooling could be used. Since no fans are used the reliability can be increased compared to solutions with fans. A very low conduction loss has been achieved by parallel connecting ten 85 mΩ normally-on JFETs in each switch position. A special gate-drive solution was applied forcing the transistors to switch very fast (approx. 20 kV/μs) resulting in very low switching losses. As the output power is almost equal to the input power a special effort was done to precisely determine the amount of semiconductor power losses via comparative thermal measurements. A detailed analysis of the measurements shows that the efficiency of the inverter is approximately 99.7% at 40 kVA.
32.	Ranstad, Per, 1958-, et al. (författare) An Experimental Evaluation of SiC Switches in Soft-Switching Converters 2014 Ingår i: IEEE transactions on power electronics. - : IEEE Press. - 0885-8993 .- 1941-0107. ; 29:5, s. 2527-2538 Tidskriftsartikel (refereegranskat)abstract Soft-switching converters equipped with insulated gate bipolar transistors (IGBTs) in silicon (Si) have to be dimensioned with respect to additional losses due to the dynamic conduction losses originating from the conductivity modulation lag. Replacing the IGBTs with emerging silicon carbide (SiC) transistors could reduce not only the dynamic conduction losses but also other loss components of the IGBTs. In the present paper, therefore, several types of SiC transistors are compared to a state-of-the-art 1200-V Si IGBT. First, the conduction losses with sinusoidal current at a fixed amplitude (150 A) are investigated at different frequencies up to 200 kHz. It was found that the SiC transistors showed no signs of dynamic conduction losses in the studied frequency range. Second, the SiC transistors were compared to the Si IGBT in a realistic soft-switching converter test system. Using a calorimetric approach, it was found that all SiC transistors showed loss reductions of more than 50%. In some cases loss reductions of 65% were achieved even if the chip area of the SiC transistor was only 11% of that of the Si IGBT. It was concluded that by increasing the chip area to a third of the Si IGBT, the SiC vertical trench junction field-effect transistor could yield a loss reduction of approximately 90%. The reverse conduction capability of the channel of unipolar devices is also identified to be an important property for loss reductions. A majority of the new SiC devices are challenging from a gate/base driver point-of-view. This aspect must also be taken into consideration when making new designs of soft-switching converters using new SiC transistors.
33.	Sadik, Diane-Perle, 1988-, et al. (författare) Analysis of short-circuit conditions for silicon carbide power transistors and suggestions for protection 2014 Ingår i: 2014 16th European Conference on Power Electronics and Applications, EPE-ECCE Europe 2014. - : IEEE. - 9781479930159 ; , s. 6910789- Konferensbidrag (refereegranskat)abstract An experimental analysis of the behavior under short-circuit conditions of three different Silicon Carbide (SiC) 1200 V power devices is presented. It is found that all devices take up a substantial voltage, which is favorable for detection of short-circuits. A suitable method for short-circuit detection without any comparator is demonstrated. A SiC JFET driver with an integrated short-circuit protection (SCP) is presented where a short-circuit detection is added to a conventional driver design in a simple way. Experimental tests of the SCP driver operating under short-circuit condition and under normal operation are performed successfully.
34.	Shisha, Samer, et al. (författare) Loss Distribution on Solid Pole Plates of Wound-Rotor Synchronous Motors Fed From Inverters Using Direct Torque Control 2012 Ingår i: IEEE transactions on energy conversion. - 0885-8969 .- 1558-0059. ; 27:1, s. 63-70 Tidskriftsartikel (refereegranskat)abstract The use of VSD (variable speed drives) is becoming prominent in industry as it has the benefit of being more energy efficient than conventional process-control mechanisms (such as throttling). VSD usually rely on the use of inverters to produce the required frequency output, which contains time harmonics that eventually induce excess losses in the machine. These losses are the subject of analysis in this study. The results show that it is possible to influence the induced current magnitude (due to the space and time harmonics) through proper design modifications, as to reduce the consequent losses. The paper focuses specifically on DTC (direct torque control) VSD application on solid pole plate synchronous machines. One of the observed effects is that the time and space harmonics are distributed differently on the pole plates.
35.	Shisha, Samer, et al. (författare) The Effect of Copper Coating on the Losses in the Solid Pole-Plates of Inverter-Fed Wound Rotor Synchronous Machines 2013 Ingår i: IEEE transactions on energy conversion. - : IEEE. - 0885-8969 .- 1558-0059. ; 28:2, s. 298-307 Tidskriftsartikel (refereegranskat)abstract The use of solid rotor and pole-plate synchronous machines has several advantages, among which is the fact that it provides a more robust rotor compared to laminated equivalents. This paper investigates the time and space harmonic losses in solid rotor synchronous machines. The work considers the use of copper coating on the pole-plates, studying the effect that this design modification has on the losses. A recommendation is given based on this study, which is considered to reduce the time harmonic losses without detrimental effects as far as the space harmonic losses are considered.
36.	Toth-Pal, Zsolt, et al. (författare) Pressure dependence of thermal contact resistance between copper heat sink and copper DBC surfaces in SiC power device packages 2014 Ingår i: Silicon Carbide and Related Materials 2013. - : Trans Tech Publications Inc.. - 9783038350101 ; , s. 1118-1121 Konferensbidrag (refereegranskat)abstract Thermal contact resistances have been measured in an experiment emulating heat transfer from a SiC die to a cooled heat sink through a heat spreader and a DBC structure. The major surface-dependent parameters are the surface roughness, surface hardness, and planarity. The measured thermal contact resistances are in agreement with theoretical values. When investigating DBC copper surfaces a second interface between the bonded Cu to AlN has to be taken into account.
37.	Velander, Erik, 1980-, et al. (författare) Novel Solutions for suppressing Parasitic Turn-on behaviour on Lateral Vertical JFETs 2014 Ingår i: Novel Solutions for suppressing Parasitic Turn-on behaviour on Lateral Vertical JFETs. - Lappeenranta. ; , s. 8- Konferensbidrag (övrigt vetenskapligt/konstnärligt)
38.	Xie, Hailian, et al. (författare) Design study of a converter interface interconnecting an energy storage with the dc-link of a VSC 2010 Ingår i: 2010 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT Europe). Konferensbidrag (refereegranskat)abstract Voltage Source Converters (VSC) have been widely utilized to provide instantaneous reactive power support to power systems, an application referred to as static synchronous compensator (StatCom). Integration of energy storage (ES) into a StatCom makes it possible for the StatCom to provide a certain amount of active power as well as reactive power support. The possible benefit of the additional active power of a StatCom can be power oscillation damping capability, mitigation of phase-jump related disturbances, etc. Direct connection of an ES device to the dc link of the VSC incurs unnecessarily high voltage rating of the VSC due to the considerable voltage swing associated with the ES device. A dual thyristor converter topology has been proposed as the interface between the ES and the dc link of the VSC. In this paper, a cost estimation for systems with the proposed interface topology is presented regarding three types of ES: capacitors, supercapacitors, and batteries. The study shows potential cost savings by utilization of the proposed interface topology. In addition, a cost comparison between different types of ES is presented, providing a guideline for the choice of ES in this kind of applications.
39.	Xie, Hailian, et al. (författare) Design Study of a Converter Interface Interconnecting Energy Storage With the DC Link of a StatCom 2011 Ingår i: IEEE Transactions on Power Delivery. - 0885-8977 .- 1937-4208. ; 26:4, s. 2676-2686 Tidskriftsartikel (refereegranskat)abstract Voltage-source converters (VSC) have been widelyutilized to provide instantaneous reactive power support topower systems, an application referred to as static synchronouscompensator (StatCom). The integration of energy storage (ES)into a StatCom makes it possible for the StatCom to provide acertain amount of active power as well as reactive power support.The possible benefit of the additional active power of aStatCom can be power oscillation damping capability, mitigationof phase-jump-related disturbances, etc. Direct connection ofan ES device to the dc link of the VSC incurs an unnecessarilyhigh-voltage rating of the VSC due to the considerable voltageswing associated with the ES device. Dual thyristor convertertopology has been proposed as the interface between the ES andthe dc link of the VSC. In this paper, a cost estimation for systemswith the proposed interface topology is presented regarding threetypes of ES: capacitors, supercapacitors, and batteries. The studyshows potential cost savings with utilization of the proposed interfacetopology. In addition, a cost comparison between differenttypes of ES is presented, providing a guideline for the choice of ES in these kinds of applications.
40.	Zdanowski, M., et al. (författare) Design and Evaluation of Reduced Self-Capacitance Inductor for Fast-Switching SiC BJT dc/dc Converters 2012 Ingår i: 2012 15TH INTERNATIONAL POWER ELECTRONICS AND MOTION CONTROL CONFERENCE (EPE/PEMC). - : IEEE. - 9781467319713 Konferensbidrag (refereegranskat)abstract The paper presents design, measurements and evaluation of the inductor with reduced self-capacitance. As an reference inductor with the same parameters but non-optimized self-capacitance is chosen. Differences in the parasitic capacitance of the inductor are validated by four measurement methods and experimentally confirmed on a 2 kW, 100 kHz dc/dc converter with silicon carbide BJTs. When the low-capacitance inductor is applied the switching performance is better, especially high-frequency resonances are limited. Additionally, it was found that the power losses were reduced by approximately 20%.
41.	Zhang, Lidong, et al. (författare) Analysis of Stability Limitations of a VSC-HVDC Link Using Power-Synchronization Control 2011 Ingår i: IEEE Transactions on Power Systems. - 0885-8950 .- 1558-0679. ; 26:3, s. 1326-1337 Tidskriftsartikel (refereegranskat)abstract In this paper, the stability limitations are analyzed for a voltage-source converter (VSC) based high-voltage direct-current (HVDC) link using power-synchronization control for two feasible operation modes: alternating-voltage control and reactive-power control. As a comparison, the analysis has been done by the phasor approach and the space-vector approach. While the phasor approach is straightforward to apply and gives intuitive analytical results, the space-vector approach reflects more dynamic insights of the system. This is achieved by using a unified dynamic modeling of both the ac system and the VSC by means of a new introduced modeling approach Jacobian transfer matrices. This approach shows that non-minimum-phase phenomena due to competing effects between alternating voltages and currents following phase-angle changes impose a fundamental limitation on the achievable bandwidth of the VSC-HVDC link. At moderate voltage levels, a VSC-HVDC link operating in alternating-voltage control mode is able to achieve higher bandwidth than in reactive-power control mode since the right-half plane (RHP) zero is located further from the origin in the former mode.
42.	Zhang, Lidong, et al. (författare) Modelling and control of VSC-HVDC connected to island systems 2010 Ingår i: IEEE Power and Energy Society General Meeting. - : IEEE. - 9781424483570 Konferensbidrag (refereegranskat)abstract The recently proposed power-synchronization control for grid-connected voltage-source converters (VSCs) has been shown to be a feasible solution for high-voltage dc (HVDC) transmission connected to high-impedance weak ac systems. In this paper, power-synchronization control is investigated for VSC-HVDC connected to another type of weak ac system, i.e., low-inertia or island systems. As an example, a linear model of a typical island system feeding by a VSC-HVDC link, including a synchronous generator, an induction motor and some passive loads, is developed for tuning the control parameters of the VSCHVDC. Time simulations in PSCAD/EMTDC demonstrate that VSC-HVDC using power-synchronization control is flexible for various network conditions, such as large-ac-system connection, island systems, or passive networks. The time simulations also show that power-synchronization control can seamlessly handle transitions between the operation modes, as well as ride through ac-system faults in all network conditions.
43.	Ängquist, Lennart, et al. (författare) Open-loop approach to control a Modular Multilevel Frequency Converter 2011 Ingår i: Proceedings of the 2011-14th European Conference on Power Electronics and Applications (EPE 2011). - 9781612841670 Konferensbidrag (refereegranskat)abstract Frequency converters are required to supply power from the public three-phase network to railways using 16.7 Hz single-phase in their rolling stock. The emerging Modular Multilevel Converter (M2C) technology offers the possibility to make such power conversion in one step using Modular Multilevel Frequency Converters (MMFC) with full-bridge sub-modules. A detailed study of the modulation and control of such converters is presented in this paper. The voltage inserted by each arm of the MMFC is a mixture of the three-phase 50 Hz voltage and the single phase 16.7 Hz voltage. It is important that the voltage reference given to the modulator will be carefully reproduced by the converter because any deviation can introduce undesired frequency components from the single-phase side to the three-phase side and vice versa. The fact that the low frequency, single-phase load causes low-frequency ripple in the total capacitor voltage complicates the problem to generate the correct modulation pattern. In this paper it is proposed to solve that difficulty by estimating the instaneous total capacitor voltages in each arm and provide that information to the modulator. It is shown that such estimations can be performed using measured currents on the single- and three-phase sides. Stable single-phase voltage, symmetrical undistorted three-phase currents and stable converter capacitor voltages are achieved under varying loading conditions. Models in Matlab/Simulink (continuous) and EMTDC/PSCAD (discrete sub-modules) have been developed in this study.
44.	Ängquist, Lennart, et al. (författare) Open-Loop Control of Modular Multilevel Converters Using Estimation of Stored Energy 2011 Ingår i: IEEE transactions on industry applications. - 0093-9994 .- 1939-9367. ; 47:6, s. 2516-2524 Tidskriftsartikel (refereegranskat)abstract The internal control of a modular multilevel converter aims to equalize and stabilize the submodule capacitor voltages independent of the loading conditions. It has been shown that a submodule selection mechanism, included in the modulator, can provide voltage sharing inside the converter arm. Several procedures for controlling the total stored energy in each converter arm exist. A new approach is described in this paper. It is based on estimation of the stored energy in the arms by combining the converter electromotive force reference, the measured alternating output current, and the known direct voltage. No feedback controllers are used. Experimental verification on a three-phase 10 kVA prototype is presented along with the description of the new procedure.

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