Circulating Current Harmonics Suppression for Modular Multilevel Converters Based on Repetitive Control

Li, Binbin; Xu, Dingbang; Xu, Dehong

doi:10.6113/jpe.2014.14.6.1100

“…Studies presented in [57] showed the interference of the PI compensator with the RC in [56]. Thus, [57] proposed the use of only a proportional gain together with the RC, first proposed in [56]. The result, once more, proved to be satisfactory.…”

Section: Control Of the MMCmentioning

confidence: 99%

Modelling, simulation, control, and enhanced topologies for the modular multilevel converter for high-voltage DC (HVDC) applications

Oliveira¹

2021

Preprint

1

0

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This thesis is focused on the modular multilevel converter (MMC) for High-Voltage DC (HVDC) systems. It is an attempt to address the issues associated with the modelling, simulation, control, efficiency, and fault-handling capability of the MMC. Thus, to address the modelling of the MMC, a new and more accurate steady-state harmonic model is proposed. The proposed harmonic model is capable of predicting the amplitude of the harmonic components of the MMC arm voltages, submodule capacitor voltages, and arm currents. Further, based on the proposed harmonic model, a capacitor sizing method is proposed to determine the capacitance of the submodule capacitor for a desired level of voltage variation, without a need for numerical algorithms or graphs used by the existing methods. In addition, the proposed capacitor sizing method can accurately determine the required capacitance even if circulating currents are injected to mitigate dc voltage fluctuations. The thesis also proposes a simple equivalent-circuit-based simulation model for MMC-based HVDC systems, which assumes ideal submodule switches to speed up the simulation, but is nonetheless capable of capturing the transients as well as harmonic components of the voltages and currents. Further, the thesis proposes a simple compensation strategy that calculates the magnitude of the second harmonic component of an arm voltage, and uses the calculated value as a feedforward signal to cancel the circulating current of the corresponding MMC leg. The proposed feedforward compensation strategy, if combined with a closed-loop circulating current suppression strategy, greatly mitigates the possibility of control saturation and, also, results in better damped closed-loop dynamics. Finally, the thesis proposes two new MMC topologies for enhanced efficiency and dc-side fault handling capability. In the first proposed topology, that is the lattice modular multilevel converter (LMMC), the entire MMC arm is modified to accommodate networks that allow shortcuts between the arm capacitors, thus, reducing conduction power losses of the converter. In the second topology proposed, however, only the submodule is modified. In the proposed submodule topology, referred to as lattice submodule (LSM), the conduction power losses are decreased, as it is the case for the LMMC, with the difference that the voltage stress in the switches are also reduced. Keywords: Control, lattice modular multilevel converter, lattice submodule, modelling, modular multilevel converter, simulation model.

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“…The described method is formed by a PI compensator and a repetitive controller (RC), and showed promised results for suppressing the circulating current. Studies presented in [57] showed the interference of the PI compensator with the RC in [56]. Thus, [57] proposed the use of only a proportional gain together with the RC, first proposed in [56].…”

Section: Control Of the MMCmentioning

confidence: 99%

Modelling, simulation, control, and enhanced topologies for the modular multilevel converter for high-voltage DC (HVDC) applications

Oliveira¹

2021

Preprint

0

View full text Add to dashboard Cite

This thesis is focused on the modular multilevel converter (MMC) for High-Voltage DC (HVDC) systems. It is an attempt to address the issues associated with the modelling, simulation, control, efficiency, and fault-handling capability of the MMC. Thus, to address the modelling of the MMC, a new and more accurate steady-state harmonic model is proposed. The proposed harmonic model is capable of predicting the amplitude of the harmonic components of the MMC arm voltages, submodule capacitor voltages, and arm currents. Further, based on the proposed harmonic model, a capacitor sizing method is proposed to determine the capacitance of the submodule capacitor for a desired level of voltage variation, without a need for numerical algorithms or graphs used by the existing methods. In addition, the proposed capacitor sizing method can accurately determine the required capacitance even if circulating currents are injected to mitigate dc voltage fluctuations. The thesis also proposes a simple equivalent-circuit-based simulation model for MMC-based HVDC systems, which assumes ideal submodule switches to speed up the simulation, but is nonetheless capable of capturing the transients as well as harmonic components of the voltages and currents. Further, the thesis proposes a simple compensation strategy that calculates the magnitude of the second harmonic component of an arm voltage, and uses the calculated value as a feedforward signal to cancel the circulating current of the corresponding MMC leg. The proposed feedforward compensation strategy, if combined with a closed-loop circulating current suppression strategy, greatly mitigates the possibility of control saturation and, also, results in better damped closed-loop dynamics. Finally, the thesis proposes two new MMC topologies for enhanced efficiency and dc-side fault handling capability. In the first proposed topology, that is the lattice modular multilevel converter (LMMC), the entire MMC arm is modified to accommodate networks that allow shortcuts between the arm capacitors, thus, reducing conduction power losses of the converter. In the second topology proposed, however, only the submodule is modified. In the proposed submodule topology, referred to as lattice submodule (LSM), the conduction power losses are decreased, as it is the case for the LMMC, with the difference that the voltage stress in the switches are also reduced. Keywords: Control, lattice modular multilevel converter, lattice submodule, modelling, modular multilevel converter, simulation model.

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“…Shunfeng Yang, Student Member, IEEE, Peng Wang, Senior Member, IEEE, Yi Tang, Member, IEEE, Michael Zagrodnik, Xiaolei Hu, Member, IEEE, and King Jet Tseng M proportional controller is proposed in [27], in order to facilitate the control system design and improve the accuracy and robustness of the control system. In this paper, an improved repetitive controller being able to exclusively cope with the even-order signals is proposed for the sake of perfect even harmonics suppression in the differential current, based on the circulating current characteristics of the MMC system.…”

Section: Circulating Current Suppression In Modular Multilevel Converters With Even-harmonic Repetitive Controlmentioning

confidence: 99%

Circulating Current Suppression in Modular Multilevel Converters With Even-Harmonic Repetitive Control

Yang

¹

,

Tang

²

,

Zagrodnik³

et al. 2018

IEEE Trans. on Ind. Applicat.

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Due to the voltage mismatch between the phase legs and the DC bus in Modular Multilevel Converters (MMCs), the differential current in MMCs is inherently subjected to circulating even order harmonics. Repetitive control based active harmonic suppression methods can be adopted to eliminate such harmonics. Nevertheless, conventional repetitive controllers have a relatively slow dynamic response because all the sampled errors in the past one cycle have to be stored, which causes a response delay for one fundamental period. This paper proposes an improved repetitive control scheme that exclusively copes with even order harmonics based on the circulating current characteristics of MMC systems. The design details of the even harmonic repetitive control scheme according to the harmonics characteristics are provided. The proposed even-harmonic repetitive control scheme requires halved data memory to store error samplings and the delay introduced by the repetitive controller is also reduced. According to the frequency domain analysis, the even-harmonic repetitive control features faster convergence rate, greater low-frequency gains, higher crossover frequency, and higher tolerance against system frequency deviation, while possessing the same even-order harmonics suppression capability and stability as conventional ones. Simulation and experimental results are presented to show the steady-state harmonics suppression capability, dynamic response, and disturbance tolerance of the proposed even-harmonic repetitive control scheme.

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Circulating Current Harmonics Suppression for Modular Multilevel Converters Based on Repetitive Control

Cited by 22 publications

References 17 publications

Modelling, simulation, control, and enhanced topologies for the modular multilevel converter for high-voltage DC (HVDC) applications

Modelling, simulation, control, and enhanced topologies for the modular multilevel converter for high-voltage DC (HVDC) applications

Modelling, simulation, control, and enhanced topologies for the modular multilevel converter for high-voltage DC (HVDC) applications

Circulating Current Suppression in Modular Multilevel Converters With Even-Harmonic Repetitive Control

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