Operation and Control Methods of Modular Multilevel Converters in Unbalanced AC Grids: A Review

Li, Jinke; Konstantinou, Georgios; Wickramasinghe, Harith R.; Pou, Josep

doi:10.1109/jestpe.2018.2856505

Cited by 93 publications

(52 citation statements)

References 97 publications

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“…It is worth mentioning that the implementation of (24) is rather straightforward regardless of the complexity of the derivation. This is because (24) mainly relies on algebraic expressions and standard averaging techniques, in addition to the output signals from the PI controllers for the energy balancing control, as defined by (12) and (13). Furthermore, notice that (24) simplifies even further when selecting one of the frontier cases α ≡ 1 or α ≡ 0.…”

Section: B Optimal Circulating Current Reference Shaping For Unbalanmentioning

confidence: 99%

“…For instance, the circulating currents can be controlled to be constant [11], or to contain a second harmonic component to compensate for second harmonic voltage or energy oscillations in each phase of the converter [12]. This flexibility can also be utilized during unbalanced grid voltage conditions, as discussed in numerous recent publications [13]. Thus, the MMC can be controlled to act as a "power oscillation firewall" or an "energy buffer" during unbalanced faults, preventing power oscillations on the ac side from propagating into the dc system.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Optimal Shaping of the MMC Circulating Currents for Preventing AC-Side Power Oscillations From Propagating Into HVdc Grids

Bergna-Diaz

Suul

Berne

et al. 2019

IEEE J. Emerg. Sel. Topics Power Electron.

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A constrained optimization problem based on the Lagrange multipliers method is formulated to derive the circulating current references of Modular Multilevel Converters (MMC) directly in abc coordinates. The resulting analytic expressions for calculating the circulating current reference signals are designed to eliminate oscillations in the dc-side power flow, independently from the ac-side operation of the MMC. As a result of the constrained optimization, the circulating currents are shaped to optimally utilize the degrees of freedom provided by the internal energy buffering capacity of the MMC, to effectively decouple the ac grid conditions from the dc bus. This property of the proposed control method makes it especially suitable for preventing oscillations due to unbalanced ac grid voltage conditions from propagating into multi-terminal HVDC systems. It is shown that the power flow at the dc-side of the MMC will be most effectively decoupled from ac-side transients if the desired steady-state power flow is imposed by acting directly on the circulating current references instead of by acting on the acside current references. The operation of an MMC controlled by the proposed approach is demonstrated by simulation studies, verifying the ability of keeping the dc power flow free of second harmonic oscillations, independently of the power control objectives applied for calculating the ac-side current references of the converter.

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Section: B Optimal Circulating Current Reference Shaping For Unbalanmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Optimal Shaping of the MMC Circulating Currents for Preventing AC-Side Power Oscillations From Propagating Into HVdc Grids

Bergna-Diaz

Suul

Berne

et al. 2019

IEEE J. Emerg. Sel. Topics Power Electron.

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show abstract

“…4(c), where Stage-I controls reactive current and Stage-II is bypassed (vII is assumed to be zero). In terms of a three-phase system, negative sequence current elimination is also feasible in asymmetrical ac fault cases [39].…”

Section: Topologies and Fundamental Functions Of The Proposed T-tmentioning

confidence: 99%

A T-Type Modular Multilevel Converter

Wang

Massoud

Williams

2021

IEEE J. Emerg. Sel. Topics Power Electron.

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This paper proposes a novel modular multilevel converter (MMC) named 'T-type MMC' (T-MMC) for reliable, controllable and efficient performance in energy conversion applications. Circuitry configurations and control structures are presented, with respect to fundamental and additional functions. The T-MMC topology consists of two solid-state power stages (Stage-I and Stage-II), which are coordinated for ac and dc fault tolerance, increased ac-side voltage synthesis, etc. Energy storage elements can be integrated into the submodules. As a result, the T-MMC based energy storage system can not only increase system inertia but maintain continuous power transmission during faults. A thyristor forcedcommutation technique facilitates actively-controlled utilization of symmetrical thyristors in the conduction path; thus T-MMC normal-mode operation losses can be equivalent to those of the conventional half-bridge MMC. Simulation and experimentation demonstrate the performance of the T-MMC. Index Terms − T-Type Modular Multilevel Converter, ac/dc fault, thyristor, energy storage system.

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“…With the development of power electronics technology, the modular multilevel converter (MMC) has received extensive attention [1][2][3]. In recent years, due to its modularity, scalability, high efficiency, good harmonic performance, fault blocking capability, etc., it has been used more and more in the industry [4][5][6][7][8], such as energy storage system, medium voltage and high power motor drive system, power distribution system, high voltage direct current transmission, and so on.…”

Section: Introductionmentioning

confidence: 99%

Tracking Control of Modular Multilevel Converter Based on Linear Matrix Inequality without Coordinate Transformation

Liu

Yang

2020

Energies

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Modular multilevel converters (MMCs) play an important role in the power electronics industry due to their many advantages such as modularity and reliability. However, one of the challenges is to suppress fluctuations of circulating current and capacitor voltage and to ensure the quality of the output current. In this paper, the upper and lower arm voltages are employed as control inputs to control the output current and circulating current which are fed back to track the desired value. Based on linear matrix inequality (LMI), the control law of the MMC with multi-input system is designed to optimize the control value. The optimum arm voltage is divided by the SM nominal capacitor voltage to determine the number of SMs inserted into the upper/lower arm. The Voltage Sorting Algorithm (VSA) is then used to suppress the capacitor voltage fluctuation. The proposed tracking control strategy is implemented in MATLAB/Simulink. The results show that even under a small number of SMs (4 per arm), the output current can track the desired values and have better harmonic performance (current THD: 5.42%,voltage THD: 5.67%), and the fluctuations of the circulating current can be suppressed. Furthermore, it has better robustness and three-phase variable load fault tolerance.

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Operation and Control Methods of Modular Multilevel Converters in Unbalanced AC Grids: A Review

Cited by 93 publications

References 97 publications

Optimal Shaping of the MMC Circulating Currents for Preventing AC-Side Power Oscillations From Propagating Into HVdc Grids

Optimal Shaping of the MMC Circulating Currents for Preventing AC-Side Power Oscillations From Propagating Into HVdc Grids

A T-Type Modular Multilevel Converter

Tracking Control of Modular Multilevel Converter Based on Linear Matrix Inequality without Coordinate Transformation

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