| 1. |
- Ahmed, Noman, et al.
(författare)
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A computationally efficient continuous model for the modular multilevel converter
- 2014
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Ingår i: IEEE Journal of Emerging and Selected Topics in Power Electronics. - : IEEE. - 2168-6777. ; 2:4, s. 1139-1148
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Tidskriftsartikel (refereegranskat)abstract
- Simulation models of the modular multilevel converter (MMC) play a very important role for studying the dynamic performance. Detailed modeling of the MMC in electromagnetic transient simulation programs is cumbersome, as it requires high computational effort and simulation time. Several averaged or continuous models proposed in the literature lack the capability to describe the blocked state. This paper presents a continuous model, which is capable of accurately simulating the blocked state. This feature is very important for accurate simulation of faults. The model is generally applicable, although it is particularly useful in high-voltage dc applications.
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| 2. |
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| 3. |
- Ahmed, Noman, et al.
(författare)
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Efficient Modeling of an MMC-Based Multiterminal DC System Employing Hybrid HVDC Breakers
- 2015
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Ingår i: IEEE Transactions on Power Delivery. - : IEEE. - 0885-8977 .- 1937-4208. ; 30:4, s. 1792-1801
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Tidskriftsartikel (refereegranskat)abstract
- The feasibility of future multiterminal dc (MTDC) systems depends largely on the capability to withstand dc-side faults. Simulation models of MTDC systems play a very important role in investigating these faults. For such studies, the test system needs to be accurate and computationally efficient. This paper proposes a detailed equivalent model of the modular multilevel converter (MMC), which is used to develop the MTDC test system. The proposed model is capable of representing the blocked-mode operation of the MMC, and can be used to study the balancing control of the capacitor voltages. In addition, the operation of the MMC when redundant submodules are included in the arms can also be studied. A simplified model of a hybrid high-voltage dc breaker is also developed. Hence, the developed test system is capable of accurately describing the behavior of the MMC-based MTDC system employing hybrid HVDC breakers, during fault conditions. Using time-domain simulations, permanent dc-side faults are studied in the MTDC system. In addition, a scheme to control the fault current through the MMC using thyristors on the ac side of the converter is proposed.
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| 4. |
- Ahmed, Noman, et al.
(författare)
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Efficient Modeling of Modular Multilevel Converters in HVDC-Grids Under Fault Conditions
- 2014
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Ingår i: 2014 IEEE PES General Meeting | Conference & Exposition. - : IEEE Computer Society. - 9781479964154 ; , s. 6939166-
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Konferensbidrag (refereegranskat)abstract
- High-voltage direct current (HVDC) grids using modular multilevel converters (M2Cs) have strongly been considered for the integration of distant renewable energy sources and also as a backbone to the existing ac-grids. The dynamic performance of the M2C is of particular interest in these grids. For electromagnetic transient (EMT) programs, modeling of HVDC-grids using detailed M2C models is unrealistic, as it requires extremely high computational effort and simulation time. In this paper an HVDC-grid test system is developed using a continuous simulation model of the M2C. The model is also capable of describing the blocking events of the M2C. Using time-domain simulations in PSCAD/EMTDC, the dynamic performance of the M2C in HVDC-grids under fault conditions is investigated. Simulation results reveal that the continuous M2C model can efficiently be used to study the dynamic performance of the M2C in HVDC-grids with high computational speed, under different fault conditions.
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| 5. |
- Ahmed, Noman, et al.
(författare)
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HVDC SuperGrids with modular multilevel converters - The power transmission backbone of the future
- 2012
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Ingår i: International Multi-Conference on Systems, Signals and Devices, SSD 2012. - : IEEE. - 9781467315906 ; , s. 6198119-
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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.
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| 6. |
- Ahmed, Noman, et al.
(författare)
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Performance of the modular multilevel converter with redundant submodules
- 2015
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Ingår i: IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781479917624 ; , s. 3922-3927
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Konferensbidrag (refereegranskat)abstract
- The modular multilevel converter (MMC) is the state-of-the-art voltage-source converter (VSC) topology used for various power-conversion applications. In the MMC, submodule failures can occur due to various reasons. Therefore, additional submodules called the redundant submodules are included in the arms of the MMC to fulfill the fault-safe operation requirement. The performance of the MMC with redundant submodules has not been widely covered in the published literature. This paper investigates the performance of the MMC with redundant submodules in the arms. Two different control strategies are used and compared for integrating redundant submodules. The response of the MMC to a submodule failure for the two strategies is also studied. Moreover, the operation of the MMC with redundant submodules is validated experimentally using the converter prototype in the laboratory.
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| 7. |
- Ahmed, Noman, et al.
(författare)
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Validation of the continuous model of the modular multilevel converter with blocking/deblocking capability
- 2012
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Ingår i: AC and DC Power Transmission (ACDC 2012), 10th IET International Conference on. - : Institution of Engineering and Technology. - 9781849197007
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Konferensbidrag (refereegranskat)abstract
- This paper presents the continuous model for the Modular Multilevel Converter (M2C). The model operates in two modes, either operating as a voltage source in deblocked mode or as a rectifying diode bridge in blocked mode. The model is validated by comparison with a detailed M2C model having 36 submodules per arm, using different control strategies. The comparison is based on time-domain simulations in PSCAD/EMTDC. The continuous model shows a very good agreement with the detailed model.
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| 8. |
- Angquist, Lennart, et al.
(författare)
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Low-Cost Ultra-Fast DC Circuit-Breaker Power electronics integrated with mechanical switchgear
- 2018
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Ingår i: 2018 IEEE INTERNATIONAL CONFERENCE ON INDUSTRIAL TECHNOLOGY (ICIT). - : IEEE. - 9781509059492 ; , s. 1708-1713
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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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| 9. |
- Antonopoulos, Antonios, et al.
(författare)
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Modular multilevel converter ac motor drives with constant torque form zero to nominal speed
- 2012
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Ingår i: 2012 IEEE Energy Conversion Congress and Exposition, ECCE 2012. - : IEEE. - 9781467308014 ; , s. 739-746
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Konferensbidrag (refereegranskat)abstract
- Modular multilevel converters (M2Cs) are shown to have a great potential in the area of medium-voltage drives. Low-distortion output quantities, combined with low average switching frequencies for the semiconductor devices create the ideal combination for very high-efficiency drives, both from an electric motor and an inverter point of view. With M2Cs the output voltage has such a low harmonic content that high-power motors can be operated without any derating. However, the large number of devices and the existence of capacitors that have to conduct the fundamental frequency current, requires more complex converter control techniques than its two-level counterpart. Special care needs to be taken under starting and operation with low frequency, where the low-frequency current may cause significant unbalance between the submodule capacitor voltages, disturb the output waveforms, and eventually cause the converter to trip. In this paper, principles for converter operation with high torque in the whole speed range, from standstill to rated speed will be investigated. The converter-control method utilizes estimation of the capacitor voltage variation, based on equations describing steady-state conditions. Experimental results from a down-scaled 12 kVA prototype converter running a loaded motor from zero up to the rated speed are provided in the paper.
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| 10. |
- Antonopoulos, Antonios, et al.
(författare)
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Modular multilevel converter AC motor drives with constant torque from zero to nominal speed
- 2014
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Ingår i: IEEE transactions on industry applications. - 0093-9994 .- 1939-9367. ; 50:3, s. 1982-1993
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Tidskriftsartikel (refereegranskat)abstract
- Modular multilevel converters are shown to have a great potential in the area of medium-voltage drives. Low-distortion output quantities combined with low average switching frequencies for the semiconductor devices create an ideal combination for very high-efficiency drives. However, the large number of devices and capacitors that have to conduct the fundamental-frequency current require more complex converter control techniques than its two-level counterpart. Special care needs to be taken for starting and operation at low speeds, where the low-frequency current may cause significant unbalance between the submodule capacitor voltages and disturb the output waveforms. In this paper, principles for converter operation with high torque in the whole speed range are investigated. Experimental results from a down-scaled 12-kVA prototype converter running a loaded motor at various speeds between standstill and the rated speed are also provided.
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