Stability Analysis of MMC/MTDC Systems Considering DC-Link Dynamics

Giudice, Davide del; Bizzarri, Federico; Linaro, Daniele; Brambilla, A.

doi:10.1109/iscas51556.2021.9401678

Cited by 5 publications

(4 citation statements)

References 22 publications

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“…For instance, the bottom 6 This amendment, albeit debatable from a design standpoint, was implemented to reduce stability margins and observe an instability caused by the insertion of inductor-based FCLs of plausible inductance. 7 The results in Figure 6 are consistent with what was reported in [53], [54]. We performed also a PAC analysis in a wider range of frequencies that extended up to 10 kHz.…”

Section: Stability Analysis Through Vector Fittingsupporting

confidence: 89%

“…To showcase this feature, we considered once again the DCS1 system and investigated as an example the possible instability triggered by the insertion of inductor-based Fault Current Limiters (FCLs) at each pole of the DC side of MMC1. This issue has been recently reported for instance in [36], [53], [54], where the authors showed that a too large inductance leads to instabilities [53], [54]. In [36] the authors came to the opposite conclusion (i.e., a too small inductance value leads to instabilities).…”

Section: Stability Analysis Through Vector Fittingmentioning

confidence: 82%

“…It is also worth pointing out that the real part of three admittances is never negative, which is a general indication of the fact that MMC1 is not prone to DC side instabilities. This aspect was considered in recent works [52]- [54], which highlighted the importance of accurate cable modeling when studying DC side stability [50]. The frequencydependence of the resistance and inductance due to skin effect improves stability margins: although the capacitive part of the admittance of the MMC may fall in some frequency ranges due to resonance phenomena, the cable resistance is sufficiently high and the inductance is sufficiently low to prevent the negative resistance of the MMC from manifesting.…”

Section: The Hvdc Linkmentioning

confidence: 99%

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Modular Multilevel Converter Impedance Computation Based on Periodic Small-Signal Analysis and Vector Fitting

Giudice

Brambilla

Linaro

et al. 2022

IEEE Trans. Circuits Syst. I

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Instability and oscillation issues originating in highvoltage direct current (HVDC) systems comprising modular multilevel converters (MMCs) are gaining increasing interest in the research community. To detect such phenomena in advance, considerable effort has been devoted recently to developing MMC models for small-signal analysis. The derivation of such models is a challenging task due to the topology and complex control structure of MMCs, which results in them having a multi-frequency response. To address this issue, scholars developed methods based on dynamic phasors and harmonic state-space modelling, which, however, require extensive pen-and-paper computations. In this paper, the periodic small-signal analysis (PAC) is adopted to determine numerically several MMCs transfer functions. Such functions can be computed between any electrical circuit node or input/output port, without the need to recast the three-phase average MMC model to derive a linear equivalent one, possibly in the DQ-frame. We show how vector fitting allows converting these functions to equivalent algebraic representations, which can be profitably used to design MMCs and study their stability following some parameter changes. To showcase this feature, we exploit one of these transfer functions to detect DC-side instability in a point-to-point HVDC system.

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Section: Stability Analysis Through Vector Fittingsupporting

confidence: 89%

Section: Stability Analysis Through Vector Fittingmentioning

confidence: 82%

Section: The Hvdc Linkmentioning

confidence: 99%

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Modular Multilevel Converter Impedance Computation Based on Periodic Small-Signal Analysis and Vector Fitting

Giudice

Brambilla

Linaro

et al. 2022

IEEE Trans. Circuits Syst. I

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“…From (1) and (2) it can be inferred that the MMC1 is characterised by a negative resistance, which is a common trait of converter-connected elements whose active and reactive power absorption is regulated. In the specific case of the IEEE14 benchmark, when the MMC1 active power reference exceeds 14.9 MW, its negative resistance becomes higher than the series resistance of the lines/transformers, thereby leading to undamped RLC oscillations [44].…”

Section: Simplified MMC Modelmentioning

confidence: 99%

Impact of Passive-Components’ Models on the Stability Assessment of Inverter-Dominated Power Grids

et al. 2022

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Power systems are experiencing some profound changes, which are posing new challenges in many different ways. One of the most significant of such challenges is the increasing presence of inverter-based resources (ibrs), both as loads and generators. This calls for new approaches and a wide reconsideration of the most commonly established practices in almost all the levels of power systems’ analysis, operation, and planning. This paper focuses specifically on the impacts on stability analyses of the numerical models of power system passive components (e.g., lines, transformers, along with their on-load tap changers). Traditionally, loads have been modelled as constant power loads, being this both a conservative option for what concerns stability results and a computationally convenient simplification. However, compared to their counterparts above, in some operating conditions ibrs can effectively be considered real constant power loads, whose behaviour is much more complex in terms of the equivalent impedance seen by the network. This has an impact on the way passive network components should be modelled to attain results and conclusions consistent with the real power system behaviour. In this paper, we investigate these issues on the ieee14 bus test network. To begin with, we assess the effects of constant-power and constant-impedance load models. Then, we replace a transmission line with a dc line connected to the network through two modular multilevel converters (mmcs), which account for the presence of ibrs in modern grids. Lastly, we analyse how and to which extent inaccurate modelling of mmcs and other passive components can lead to wrong stability analyses and transient simulations.

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