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Modular multilevel converters (M2C) are increasingly used in high voltage direct current (HVDC) systems. The efficiency of M2Cs is highly related to the modulation method which determines the switching frequency and capacitor voltage ripple in the converter station. A new approach to modulation of M2C is presented in this paper. Tolerance-band methods are employed to obtain switching instants, and...
The change to a sustainable energy supply advances further development in grid interconnection, especially for offshore wind farms. This enables future wind farms to be interconnected by high voltage dc transmission grids. In this paper, a case study for dc grid with integrated offshore wind farms is studied and a system control is developed.
The necessary shift from fossil fuels to regenerative sources imposes a great challenge for future power transmission. A large, meshed HVDC-Grid is proposed by several experts as the best and most efficient solution. For meshed DC-Grids, however, new and essential requirements — especially regarding availability and reliability — have to be researched very thoroughly. Fast and reliable handling of...
In order to mitigate economical, ecological and technological challenges aircraft manufacturers have shifted towards more electrical aircraft, bringing with it many new technologies to be implemented and a redesign of the existing electrical network. This paper details the development of an electrical distribution centre as taking place under the European Framework 7 Clean Sky Program. The developed...
This paper presents the modeling and control of a multilevel DC/DC bidirectional converter suitable for medium voltage and power applications, with a special interest in wind-power applications. The proposed multilevel topology has a modular structure constituted by base DC/DC converter cells. The multilevel converter is consequently based on Dual Active Bridge (DAB). The overall control of the DC/DC...
Negative sequence currents are obtained during ac-side asymmetrical faults of converters in highvoltage direct current (HVDC) transmission systems. Consequently, second order harmonics in the dc-side voltage and current, unbalanced ac-side currents, and power oscillations can be observed. This paper presents a negative sequence current control (NSCC) scheme that eliminates second order harmonic ripples...
Simulation is a key tool for assessing the performance of new DC Electrical Power System (EPS) developments for helicopter applications. Scalable model description allows performing complete tests to verify the compliance of requirements within aeronautic electrical system standards. This approach improves computation times and robustness of simulations for complete EPSs by using models which are...
Multiterminal High Voltage Direct Current (MTDC) grids based on Voltage Source Converters (VSC) are considered ideal for the future integration of large scale and highly distributed renewable power generation, as well as interconnection of remote power systems. The control of such grids is challenging as it is necessary to provide accurate power flow control and multiple voltage controlling stations...
Unidirectional power flow voltage source converter high voltage direct current (VSC-HVDC) systems can be advantageously used in future dc subsea electric transmission and distribution systems (DC-SETDS) in order to reduce cost, increase efficiency and reliability. This work proposes a unidirectional modular multilevel converter (uMMC) suitable for VSC-HVDC systems used in DC-SETDS. The main advantage...
A per-phase sub-module capacitor voltage balancing scheme for the Alternate Arm Converter (AAC) is proposed. Leg balancing regulates the sum of sub-module capacitor voltages in a leg to its set-point. Arm balancing regulates each sub-module capacitor voltage to the nominal sub-module capacitor voltage. Additional converter control requirements and the modulation scheme are also discussed. The control...
This work presents a generalized and versatile control approach for Modular Multilevel Converters using Lagrange Multipliers in the ABC frame. The methodology is capable of analytically obtaining desired operative conditions by calculating the differential current references previously established by the constraints in the optimization formulation, whilst obtaining the result with minimum I) differential...
This paper deals with the design of high power density DC/DC buck converter for portable bench space charge measurements in full-size HVDC cables. The design of a coupled interleaved buck converter used for delivering the necessary regulated high transient current (up to 1200A during one or two seconds) is presented. The structure is original regarding its compacity and the use of an innovative, small...
For the upcoming need to transfer bulk power over long onshore distances, HVDC power transmission is the preferred choice. However, components like HVDC-DC converters and a protection concept for DC line faults present challenges, that still have to be solved. As up today, the sections of a segmented DC transmission corridor would still be linked via an AC connection, leading to high transformation...
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.
VSC technology is now well established in HVDC and is, in many respects, complementary to the older Line Commutated Converter (LCC) technology. Many advantages have been claimed for VSC technology in HVDC, including the smaller site footprint. On the other hand, VSC HVDC stations have higher power losses than LCC stations. Although the relative advantages and disadvantages are well known within the...
A current source modular multilevel converter (MMC) is proposed for high voltage AC/DC power conversion applications, such as HVDC and FACTS. Current source converters possess the advantage of short-circuit fault tolerance, which is a pivotal feature for grid applications. By partially following the circuit duality transformations, the proposed converter is derived from the well-known voltage source...
A detailed analysis of the behaviour of a Modular Multilevel Converter (MMC) in a HVDC system, in case of both DC and AC faults, is provided. Results related to a two-terminal HVDC system are presented.
HVDC transmission becomes more important for wind farms located over hundred kilometres from the shore. For offshore wind farms decoupled by HVDC transmission, frequency is a degree of freedom. State of the art for offshore wind farms is a 50Hz AC distribution grid. In this paper the effects of a higher line frequency on the main parts of an offshore wind farm are investigated. The main advantages...
The modular multilevel converter is a suitable converter topology for high-voltage high-power applications and consists of series-connected submodules. Typically, these submodules are half-bridges with dc capacitors. A voltage ripple in the submodule capacitors is inevitable due to the current flowing in the arms. The converter should therefore be controlled in such a way that the capacitor voltages...
The nacelle weight reduction is a key design criterion for offshore wind turbines, when these are reaching towards 10 MW. To overcome the weight challenge, a transformer-less concept is under development. This concept employs a special permanent magnet synchronous generator (PMSG) with an innovative system for high insulation level. The generator supplies nine series connected converter modules, which...
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