Operation of a Modular Multilevel Converter Controlled as a Virtual Synchronous Machine

DrArco, Salvatore; Guidi, Giuseppe; Suul, Jon Are

doi:10.23919/ipec.2018.8508009

Cited by 17 publications

(25 citation statements)

References 24 publications

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“…This also implies that the configuration of the energy balancing and power flow control of an MMC can have significant impact on the potential for utilizing internally stored energy and/or power from the dcside to provide inertial response from an MMC HVDC terminal. Thus, previous studies of inertia emulation and control of HVDC terminals as virtual synchronous machines (VSMs), based on 2L VSCs [42] or on MMCs with conventional CCSC [43], will not provide accurate representation of MMCs with closed loop control of the dc-side current and/or the internally stored energy.…”

Section: Phase Independent Energy Controlmentioning

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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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: Phase Independent Energy Controlmentioning

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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“…Compared to the implementation presented in [25], the control scheme defined by Fig. 2 a) and b) is completed with circulating current controllers and balancing algorithms for the MMC, based on the implementation presented in [21].…”

Section: A Current Controlled Vsmmentioning

confidence: 99%

“…A Voltage Controlled VSM (VCVSM) is considered based on the implementation from [21]. Most of the general control blocks for the VCVSM are identical to the CCVSM, including the inertia model, the reactive power controller, as well as the circulating current controller and modulation strategies for operating the MMC.…”

Section: B Voltage Controlled Vsmmentioning

confidence: 99%

“…However, the sorting algorithm for the internal voltage balancing and the generation of the gate signals for the individual converter modules are generated individually for each arm of the converter by a distributed control system. Further information about the implementation is provided in [21]. The communication for transferring the command signals from the OPAL-RT target to the MMCs and the measurement and monitoring signals sent back from the MMCs is executed via a dedicated high-speed, full-duplex fiber-optical bus operating at 5 Mbit/s.…”

Section: A Modular Multilevel Converter (Mmc)mentioning

confidence: 99%

“…While new VSC HVDC systems are usually based on Modular Multilevel Converter (MMC) technology, most previous studies of control strategies for providing virtual inertia have assumed simplified converter models corresponding to 2-level VSCs. Although some recent publications have considered implementation of virtual inertia control (VIC) for MMC-based HVDC systems, as for instance [19]- [21], the detailed interaction with the inertial response of a power system has not been studied in detail. Furthermore, experimental demonstrations of MMCs controlled for providing virtual inertia under realistic network conditions are not available in the literature.…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of Virtual Inertia Control Strategies for MMC-based HVDC Terminals by P-HiL Experiments

D’Arco

Nguyen

Suul

2019

IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society

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This paper presents an experimental performance evaluation of different control strategies for providing virtual inertia from power electronic converters. The evaluation is based on a laboratory-scale prototype of a point-to-point HVDC transmission system with Modular Multilevel Converters (MMCs). Operation with a grid emulator connected to a realtime simulator reproduces the behavior of a power system and allows Power-Hardware-in-the-Loop (P-HiL) experiments. Control of the inverter terminal for providing virtual inertia to the simulated power system is evaluated with four different control system implementations. The four cases include a conventional control system enhanced with df/dt-based inertia emulation functionality and three different Virtual Synchronous Machine (VSM) implementations based on emulation of a synchronous machine swing equation. The dynamic response in the power flow and the frequency transients are evaluated for all cases, and the inertial energy exchanged with the isolated power system is assessed in comparison to a conventional power controller without inertia emulation. The results demonstrate that all the evaluated implementations can provide similar inertial response when operated in a small isolated grid, while clear differences in dynamic response and stability properties are revealed during operation under strong grid conditions.

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Operation of a Modular Multilevel Converter Controlled as a Virtual Synchronous Machine

Cited by 17 publications

References 24 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

Evaluation of Virtual Inertia Control Strategies for MMC-based HVDC Terminals by P-HiL Experiments

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