Operating Region of Modular Multilevel Converter for HVDC With Controlled Second-Order Harmonic Circulating Current: Elaborating P-Q Capability

Kim, Heejin; Kim, Sang-Min; Chung, Yong-Ho; Yoo, Dong-Wook; Kim, Chan-Ki; Hur, Kyeong

doi:10.1109/tpwrd.2015.2458038

Cited by 44 publications

(42 citation statements)

References 52 publications

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“…Probably the most important variable of the MMC is the internal circulating current that affects the semiconductor rating because of the arm peak current and capacitor voltage ripple [27]. In fact, it may also have an effect on the operating range of the MMC under balanced conditions [27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Local Carrier PWM for Modular Multilevel Converters with Distributed PV Cells and Circulating Current Reduction

et al. 2020

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A new topology has been recently proposed for grid-connected photovoltaic (PV) systems, using modular multilevel converters (MMCs) and distributing PV panels throughout the MMC cells. This topology has two main advantages: it reduces the power losses related to moving the energy into the MMC capacitors from an external source, and it removes the losses and costs related to the DC to DC converters used to track the maximum power point on string converters or central converters, because that task is delegated to MMC cells. However, traditional pulse width modulation (PWM) techniques have many problems when dealing with this application: the distortion at the output increases to unacceptable values when MMC cells target different voltages. This paper proposes a new modulation technique for MMCs with different cell voltages, taking into account the measured cell voltages to generate switching sequences with more accurate timing. It also adapts the modulator sampling period to improve the transitions from level to level, an important issue to reduce the internal circulating currents. The proposed modulation has been validated using simulations that show a consistent behavior in the output distortion throughout a wide operation range, and it also reduces the circulating currents and cuts the conduction losses by half. The behavior of this new topology and this new modulation has been compared to the mainstream topology with external PV panels and also to a fixed carrier modulation.

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Section: Introductionmentioning

confidence: 99%

Local Carrier PWM for Modular Multilevel Converters with Distributed PV Cells and Circulating Current Reduction

et al. 2020

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“…Alternatively, overload capability might be achieved without significantly over-sizing the semiconductor devices through the use of controlled circulating currents that reduce the peak current flowing through the converter for a given set-point. Such techniques were initially proposed in [7], [8] as a method of maximizing the overall P/Q capability of MMCs and are now well established strategies [9]. These methods can expand the active power processing capability of the converter by approximately 30%.…”

Section: Introductionmentioning

confidence: 99%

“…In addition to the peak current handling capability limitations of MMCs, restrictions on the junction temperatures of the IGBT devices also have to be enforced. In [7]- [9] the influence of converter temperature dynamics on the achievable overload were neglected. Overload capability of MMC-based HVDC systems considering the temperature dynamics within the converter has arguably only been discussed in [10] and [11].…”

Section: Introductionmentioning

confidence: 99%

Dynamic Overload Capability of VSC HVDC Interconnections for Frequency Support

Sanz

Judge

Spallarossa

et al. 2017

IEEE Trans. Energy Convers.

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In future power systems reduced overall inertia caused by an increased dominance of asynchronous generation and interconnections would make frequency control particularly challenging. As the number and power rating of Voltage Source Converter (VSC) HVDC systems increases, network service provision would be expected from such systems and to do so would require overload capacity to be included in the converter specifications. This paper studies the provision of frequency services from Modular Multilevel Converter (MMC)-based VSC HVDC interconnections using temperature-constrained overload capability. Overload of the MMC-based HVDC system is achieved through controlled circulating currents, at the expense of higher losses, and subject to a control scheme which dynamically limits the overload available in order to keep the semiconductor junction temperatures within operational limits. Two frequency control schemes that use the obtained overload capacity to provide frequency response during emergency conditions are investigated. The controllers' performance is demonstrated in the context of the future Great Britain transmission grid through a reduced equivalent test system. Simulation results show that even modest temperature margins which allow overload of MMCbased HVDC systems for a few seconds are effective as a primary frequency reserve and also reduce the loss of infeed requirements of such interconnections.

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“…The MMC has numerous stacks of identical converters called submodules [1][2][3][4][5]. For the half bridge configuration, a submodule has two switching devices implemented by antiparallel connections of a fully controllable insulated-gate bipolar transistor (IGBT) and capacitor to generate the output voltage [6] (See Fig.…”

Section: Introductionmentioning

confidence: 99%

“…Because the capacitor voltage balancing should be the most basic yet critical functionality of the MMC, various balancing techniques of the capacitor voltage have been discussed in [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Reference [1] deals with two types of pulse width modulated MMC (PWM-MMC), focusing on their circuit configurations and voltage balancing control.…”

Section: Introductionmentioning

confidence: 99%

Trade-Off Strategies in Designing Capacitor Voltage Balancing Schemes for Modular Multilevel Converter HVDC

Nam¹,

Kim²,

Kim³

et al. 2016

Journal of Electrical Engineering and Technology

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-This paper focuses on the engineering trade-offs in designing capacitor voltage balancing schemes for modular multilevel converters (MMC) HVDC: regulation performance and switching loss. MMC is driven by the on/off switch operation of numerous submodules and the key design concern is balancing submodule capacitor voltages minimizing switching transition among submodules because it represents the voltage regulation performance and system loss. This paper first introduces the state-ofthe-art MMC-HVDC submodule capacitor voltage balancing methods reported in the literatures and discusses the trade-offs in designing these methods for HVDC application. This paper further proposes a submodule capacitor balancing scheme exploiting a control signal to flexibly interchange between the on-state and the off-state submodules. The proposed scheme enables desired performance-based voltage regulation and avoids unnecessary switching transitions among submodules, consequently reducing the switching loss. The flexibility and controllability particularly fit in high-level MMC HVDC applications where the aforementioned design trade-offs become more crucial. Simulation studies for MMC HVDC are performed to demonstrate the validity and effectiveness of the proposed capacitor voltage balancing algorithm.

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Operating Region of Modular Multilevel Converter for HVDC With Controlled Second-Order Harmonic Circulating Current: Elaborating P-Q Capability

Cited by 44 publications

References 52 publications

Local Carrier PWM for Modular Multilevel Converters with Distributed PV Cells and Circulating Current Reduction

Local Carrier PWM for Modular Multilevel Converters with Distributed PV Cells and Circulating Current Reduction

Dynamic Overload Capability of VSC HVDC Interconnections for Frequency Support

Trade-Off Strategies in Designing Capacitor Voltage Balancing Schemes for Modular Multilevel Converter HVDC

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