Improving capacitor voltage ripples and power losses of modular multilevel converters through discontinuous modulation

Abstract-Whilst third harmonic injection is extensively used in modular multilevelconverter (MMC) control, its significant advantages over sinusoidal modulation have not been fully explored. This paper evaluates the influence of third harmonic injection on system power losses, submodule capacitance, circulating current, and fault current and mathematical models are derived. Station conduction losses are reduced by 11%, yielding higher efficiency and lowering cooling system capacity. The submodule capacitance is reduced by 24%, which significantly lowers the capital cost, weight, and volume of the station converter. Additionally, the phase energy variation is reduced by around 18%, which benefits circulating current control. Due to the lower AC currents, the semiconductor current stresses are correspondingly reduced. In addition to the performance improvement in normal operation, the third harmonic injection reduces the DC fault currents by 13.4% and thus the fault current stresses on semiconductors and DC circuit breakers are lowered. Simulation of a point-to-point HVDC system demonstrates the effectiveness of the above analysis.Index Terms-DC fault current, HVDC transmission, modular multilevel converter (MMC), power loss, submodule capacitance, third harmonic injection.

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“…By injecting the triplen harmonics, the DC voltage utilization ratio is increased from ½ to 1 3 [7,14].…”

Section: Modular Multilevel Converter (Mmc) Deployment For Hvdc Transmentioning

confidence: 99%

Influence of third harmonic injection on modular multilevel converter ‐based high‐voltage direct current transmission systems

Fletcher

Williams

2016

IET Generation, Transmission & Distribution

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“…A preliminary study on the discontinuous modulation applied to the MMC was presented in [19]. The discontinuous modulation aims to reduce the switching power losses and the capacitor voltage ripples, especially at low modulation indices.…”

Section: Introductionmentioning

confidence: 99%

“…Although some interesting results were shown in [19], the reductions achieved in the capacitor voltage ripples and switching power losses were not optimized. This is because the clamping intervals of the reference signals were fixed and could not be changed.…”

Section: Introductionmentioning

confidence: 99%

Closed-Loop Discontinuous Modulation Technique for Capacitor Voltage Ripples and Switching Losses Reduction in Modular Multilevel Converters

Picas

Ceballos

Pou

et al. 2015

IEEE Trans. Power Electron.

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In this paper, a new discontinuous modulation technique is presented for the operation of the modular multilevel converter (MMC). The modulation technique is based on adding a zero-sequence to the original modulation signals so that the MMC arms are clamped to the upper or lower terminals of the dc-link bus.The clamping intervals are controlled according to the absolute value of the output current to minimize the switching losses of the MMC. A significant reduction in the capacitor voltage ripples is achieved, especially when operating with low modulation indices. Furthermore, a circulating current control strategy suitable for this modulation technique is also proposed. Simulation and experimental results under various operating points are reported along with evaluation and comparison results against a conventional carrier-based pulse-width modulation method.

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“…When applying the discontinuous modulation to the MMC [8], [9], all the SMs of one arm of a particular phase-leg are deactivated (bypassed) for some intervals. Therefore, the phase-leg is clamped to the upper or lower dc-bus terminals.…”

Section: A Basics Of Discontinuous Modulationmentioning

confidence: 99%

“…Another method that can be used for reducing the capacitor voltage ripples is discontinuous modulation [8], [9]. This technique is based on clamping one arm of the converter to a nonswitching position.…”

Section: Introductionmentioning

confidence: 99%

Discontinuous modulation of modular multilevel converters without the need for extra submodules

Picas

Ceballos

Pou

et al. 2015

IECON 2015 - 41st Annual Conference of the IEEE Industrial Electronics Society

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Abstract-In this paper, a new approach to the discontinuous modulation technique for the operation of the modular multilevel converter (MMC) is presented. Discontinuous modulation is based on adding a zero-sequence to the original modulation signals so that each MMC arm is clamped to the upper or lower terminals of the dc-link bus during some intervals. In combination with a circulating current control, the original discontinuous modulation can reduce the capacitor voltage ripple amplitudes and the switching power losses. However, additional submodules (SMs) are required to control the circulating current. This new approach presents a clamping algorithm that eliminates the requirement of additional SMs. As a result, the conduction losses are reduced while the capacitor voltage ripples are maintained low. Simulation and experimental results on a silicon-carbidebased MMC are reported and compared against the original discontinuous modulation and a conventional carrier-based pulsewidth modulation.

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Improving capacitor voltage ripples and power losses of modular multilevel converters through discontinuous modulation

Cited by 16 publications

References 16 publications

Influence of third harmonic injection on modular multilevel converter ‐based high‐voltage direct current transmission systems

Influence of third harmonic injection on modular multilevel converter ‐based high‐voltage direct current transmission systems

Closed-Loop Discontinuous Modulation Technique for Capacitor Voltage Ripples and Switching Losses Reduction in Modular Multilevel Converters

Discontinuous modulation of modular multilevel converters without the need for extra submodules

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