Controlled islanding algorithm for AC/DC hybrid power systems utilising DC modulation

Abstract

The controlled islanding problem is typically considered only for pure ac power systems, with the ultimate objective of either minimising power imbalance or power-flow among islands. However, as ac/dc hybrid power systems are becoming popular worldwide, current controlled islanding schemes should be redesigned to take into account the presence of high-voltage dc (HVDC) links, possibly connecting different islands. Accordingly, in this study, the authors solve the classic islanding problem combining HVDC power modulation with the conventional ac cutset search. The flexibility of the HVDC allows the authors' strategy to jointly capture the previously mentioned objectives, and provides even lower power imbalances than the minimum imbalance strategy, at a relatively small cost of increasing power-flow impact. Then, the optimisation problem is formulated as a mixed-integer linear programming problem, which can be conveniently solved with existing commercial solvers. Finally, they validate their proposed strategy in two case studies, corresponding to a modified IEEE-118 system and to the China Southern Power Grid system. In both cases, dynamic simulations show that their proposed approach outperforms classic algorithms where the presence of HVDC power modulation is not explicitly taken into account.

Consensus-Based Distributed Intentional Controlled Islanding of Power Grids

“…The cost function in (3) has been used in previous work in the literature on grid partitioning, e.g. [13], [19], [26], as an indicator of the ability of a power system to satisfy the loads' demand, which is also known as adequacy [39].…”

“…To test our algorithm under different conditions, we considered different choices Π(0). In some cases, we took as Π(0) some selected partitions from [13], [27], [43]. In other cases, to generate Π(0), we first employ the Search Space Reduction Procedure (SSRP) [27], which generates a spanning tree connecting groups of coherent generators (these are taken from [27]).…”

“…We assume that the migration process is triggered by a three phase solid ground fault at bus 15 forcing line 14-15 to disconnect. With 𝑛 𝜇 = 2, we ran the algorithm first by considering as initial partition Π(0) the one generated by SSRP+BFS and then using as Π(0) the final partition reported in [13] to evaluate how it performed when started from different initial partitions. For the case 𝑛 𝜇 = 3, we considered as Π(0) the partition generated via SSRP+BFS and then the final one obtained in [27].…”

“…When the control architecture fails to guarantee reliable operation of the transmission grid, last resort strategies have been devised so as to ensure power dispatchment across at least some of its sections. Strategies for Intentional Controlled Islanding (ICI) address this issue [13]- [17] by identifying sections of the grid (or islands) that can isolate and operate independently from the rest of the network. Recently, intentional islanding has also been proposed in the framework of distribution networkssee [18] and references therein-as the presence of storage devices and renewable energy generation allow these grids to be partitioned into networks of microgrids, e.g., [19]- [21].…”

“…The problem of partitioning a grid into a set of islands (that do not exchange power among each other) is usually posed as a combinatorial problem-see for example [19], [23]- [25]-and sometimes is recast as a graph optimization problem [15]- [17]. Solving this problem numerically can be computationally expensive, so that heuristic strategies are frequently used to seek a suboptimal solution, while meeting the required computational time that allows the network to stabilize after a contingency [13], [26]- [28]. The centralized techniques used to solve the islanding problem include spectral clustering over simple [22] or multi-layer graphs [29], ant colony optimization algorithms [30], or particle swarm optimization [31].…”