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L. Sigrist

Publications and source records attributed to L. Sigrist.

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Sinusoidality Index

Maintaining sinusoidal or near-sinusoidal operating conditions in electrical systems is essential, as is their accurate assessment. This letter proposes a novel metric, namely the sinusoidality index, which quantifies the instantaneous deviation of the trajectory of an ac voltage vector with respect to a circle under any periodic operating conditions. This metric differs from conventional Fourier-based estimations by accounting for the trajectory of the waveform rather than its spectral decomposition. A variety of examples illustrates the properties of the proposed metric and highlights insights that may not be captured by conventional approaches.

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Theoretical and Experimental Limitations of RoCoF Estimation

A precise estimation of the Rate of Change of Frequency (RoCoF) is crucial for secure power system operation. In fact, RoCoF is strictly related to the amount of the available physical and/or virtual inertia of the system and the severity of the active power unbalance following a disturbance. For this reason, it is widely exploited in different protection systems, e.g., Anti-Islanding, Under Frequency Load Shedding (UFLS) and wide-area protection systems. The new paradigm of modern power systems, with a low-inertia and converter-based generation assets, is increasing the transient severity, making the frequency and the RoCoF estimation more complex and less precise for the actual devices. This work addresses this issue by proposing a numerically robust approach based on concepts inherited from differential geometry and fluid mechanics. The proposed approach is then tested with high-sampling real experimental measurements and used to develop a faster control logic for a RoCoF-based UFLS control scheme. The proposed approach provides information to protections regarding the nature of the contingency which can be used to improve its response.

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Dynamic Virtual Power Plant: A New Concept for Grid Integration of Renewable Energy Sources

The notion of Virtual Power Plant (VPP) has been used many times in last years in power systems and for several reasons. As a general trend, the behavior of a classic synchronous generator is to be emulated for a class of conventional grid components like, e.g., renewable generators or/and power electronic units. Most of the times production of these units is of interest, as it is the case for the new AGC scheme of Spain which, from this point of view, looks like a VPP. However, dynamic aspects are of high importance, especially for increasing the actual rate of penetration of Renewable Energy Sources (RES). Indeed, to go above the actual rate of RES penetration, one should deal with full participation of RES to grid services. For that, we propose here a new concept called Dynamic VPP (DVPP) which fully integrates the dynamic aspects at all levels: locally (for each RES generator), globally (for grid ancillary services and interaction with other neighbor elements of the grid) and economically (for internal optimal dispatch and participation to electricity markets). A DVPP is a set of RES along with a set of control and operation procedures. This means methodologies for: choosing the participating RES, optimal and continuous operation as a whole (especially in case of loss of natural resources - e.g., wind, sun - on a part of the DVPP), regulation (in the dynamic sense) to ensure local objectives for each generator, participation to ancillary services of the DVPP as a unit and to diminish negative effects of interaction with neighbor dynamics elements of the power system, integration in both actual power systems scenarios (with mixed classic and power electronics based generation) and future ones with high degree of RES penetration.

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