MMC Based MTDC Grids: A Detailed Review on Issues and Challenges for Operation, Control and Protection Schemes

Ansari, Jamshed Ahmed; Liu, Chongru; Khan, Shahid

doi:10.1109/access.2020.3023544

Cited by 58 publications

(31 citation statements)

References 105 publications

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“…A basic outline of the MMC topology is shown in Figure 12 [ [133][134][135]. There are several possible submodule topologies, including the half-bridge (HB), full-bridge, and fivelevel cross connected modules.…”

Section: Converters 411 Ac-dc and Dc-ac Convertersmentioning

confidence: 99%

“…Dealing with short circuit currents is predicted to be a great difficulty in DC grids [84], and compared to AC systems, the protection in DC will be much more complex [79]. This is partly due to the fact that in AC systems, power flow is generally in one direction; however, due to bidirectional converters, a DC fault is often propagated to all of the interconnected converters in DC systems [134]. The increase in power electronics also adds to the system complexity in terms of protection.…”

Section: Overviewmentioning

confidence: 99%

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Review of MVDC Applications, Technologies, and Future Prospects

Coffey

Timmers

et al. 2021

Energies

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This paper presents a complete review of MVDC applications and their required technologies. Four main MVDC applications were investigated: rail, shipboard systems, distribution grids, and offshore collection systems. For each application, the voltage and power levels, grid structures, converter topologies, and protection and control structure were reviewed. Case studies of the varying applications as well as the literature were analyzed to ascertain the common trends and to review suggested future topologies. For rail, ship, and distribution systems, the technology and ability to implement MVDC grids is available, and there are already a number of case studies. Offshore wind collection systems, however, are yet able to be implemented. Across the four applications, the MVDC voltages ranged from 5–50 kV DC and tens of MW, with some papers suggesting an upper limit of 100 kV DC and hundreds of MV for distribution networks and offshore wind farm applications. This enables the use of varying technologies at both the lower and high voltage ranges, giving flexibility in the choice of topology that is required required.

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Section: Converters 411 Ac-dc and Dc-ac Convertersmentioning

confidence: 99%

Section: Overviewmentioning

confidence: 99%

Review of MVDC Applications, Technologies, and Future Prospects

Coffey

Timmers

et al. 2021

Energies

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“…M ODULAR multilevel converters (MMC) are key components in many existing and emerging high power system applications [1], [2], such as wind or photovoltaic energy conversion systems [3], high voltage direct current transmission systems [4], electric ships [5] and multiterminal dc grids [6], [7]. In all these applications -in particular in possible multiterminal dc grids -MMCs will increasingly have the task to control and to electronically protect the associated ac and dc grids and themselves even during fast transients and unexpected severe fault conditions.…”

Section: Introductionmentioning

confidence: 99%

Direct Multivariable Control for Modular Multilevel Converters

Dinkel

Hillermeier

Marquardt

2022

IEEE Trans. Power Electron.

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Modular multilevel converters (MMC) have enabled new and demanding applications for power electronics in the high voltage/high power range. In these applications very fast and tight control of all variables of the MMC is of prime importance. This paper presents a new multivariable control (MVC) concept, which enables independent and extremely fast control of all essential variables. For each variable a tolerance band can be specified, which is strictly met even under unexpected severe transients and disturbances. The minimized dead times achieved by the control are more than one order of magnitude smaller than the state of the art. The MVC has been implemented based on FPGA-hardware and digital signal processing of the measured values. Experimental results of the control performance and the robustness against parameter variation are presented, using a down scaled MMC with 96 submodules. These results include the analysis of steady state operation, dynamic performance and fault scenarios.

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“…N OWADAYS, the modular multilevel converter (MMC) is a prominent solution for high voltage direct current (HVDC) transmission systems [1], [2] and for medium voltage drive applications [3], [4]. The main benefits of the MMC are its modularity and scalability to reach high voltage requirements, high efficiency, low harmonic distortion, transformerless operation, and reduced dv/dt in each switch [5], [6].…”

Section: Introductionmentioning

confidence: 99%

Experimental Validation of a Nested Control System to Balance the Cell Capacitor Voltages in Hybrid MMCs

et al. 2021

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In a hybrid modular multilevel converter (MMC), capacitor voltage balance between the Full-Bridge Sub-Modules (FBSMs) and Half-Bridge Sub-Modules (HBSMs) is only possible when the arm currents are bipolar. For a grid-connected MMC, operating at unity power factor, this is typically achievable when the modulation index is less than 2. Previous control methodologies, based on open-loop feed-forward compensating currents, have been proposed to operate an MMC with a higher modulation index. However, these solutions do not minimize the compensating currents; they cannot compensate entirely for both the variations in the operating conditions and the parameters typically encountered in a real implementation; and they do not consider the actual capacitor voltage imbalance between the FBSM and HBSMs. In this paper, a new nested closed-loop control algorithm based on an outer voltage control loop with an inner current loop is proposed and experimentally validated. Feed-forward currents are still utilised in the inner loop, but they are calculated using a new optimising algorithm which minimises the required compensating currents. Moreover, to the best of our knowledge, this is the first work where explicit algebraic equations to calculate these compensating currents are provided. Experimental results to validate the approach, obtained with an 18-cell hybrid MMC, are presented and discussed in the paper.

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MMC Based MTDC Grids: A Detailed Review on Issues and Challenges for Operation, Control and Protection Schemes

Cited by 58 publications

References 105 publications

Review of MVDC Applications, Technologies, and Future Prospects

Review of MVDC Applications, Technologies, and Future Prospects

Direct Multivariable Control for Modular Multilevel Converters

Experimental Validation of a Nested Control System to Balance the Cell Capacitor Voltages in Hybrid MMCs

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