| 1. |
- Andreasson, Martin, et al.
(författare)
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Coherence in Synchronizing Power Networks with Distributed Integral Control
- 2017
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Ingår i: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017. - : IEEE. - 9781509028733 ; , s. 6683-6688
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Konferensbidrag (refereegranskat)abstract
- We consider frequency control of synchronous generator networks and study transient performance under both primary and secondary frequency control. We model random step changes in power loads and evaluate performance in terms of expected deviations from a synchronous frequency over the synchronization transient; what can be thought of as lack of frequency coherence. We compare a standard droop control strategy to two secondary proportional integral (PI) controllers: centralized averaging PI control (CAPI) and distributed averaging PI control (DAPI). We show that the performance of a power system with DAPI control is always superior to that of a CAPI controlled system, which in turn has the same transient performance as standard droop control. Furthermore, for a large class of network graphs, performance scales unfavorably with network size with CAPI and droop control, which is not the case with DAPI control. We discuss optimal tuning of the DAPI controller and describe how internodal alignment of the integral states affects performance. Our results are demonstrated through simulations of the Nordic power grid.
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| 2. |
- Milošević, Jezdimir, et al.
(författare)
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Exploiting Submodularity in Security Measure Allocation for Industrial Control Systems
- 2017
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Ingår i: Proceedings of the 1st ACM Workshop on the Internet of Safe Things. - New York, NY, USA : ACM. ; , s. 64-69
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Konferensbidrag (refereegranskat)abstract
- Industrial control systems are cyber-physical systems that are used to operate critical infrastructures such as smart grids, traffic systems, industrial facilities, and water distribution networks. The digitalization of these systems increases their efficiency and decreases their cost of operation, but also makes them more vulnerable to cyber-attacks. In order to protect industrial control systems from cyber-attacks, the installation of multiple layers of security measures is necessary. In this paper, we study how to allocate a large number of security measures under a limited budget, such as to minimize the total risk of cyber-attacks. The security measure allocation problem formulated in this way is a combinatorial optimization problem subject to a knapsack (budget) constraint. The formulated problem is NP-hard, therefore we propose a method to exploit submodularity of the objective function so that polynomial time algorithms can be applied to obtain solutions with guaranteed approximation bounds. The problem formulation requires a preprocessing step in which attack scenarios are selected, and impacts and likelihoods of these scenarios are estimated. We discuss how the proposed method can be applied in practice.
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| 3. |
- Sasahara, Hampei, et al.
(författare)
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Glocal Control for Network Systems via Hierarchical State-Space Expansion
- 2017
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Ingår i: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017. - : IEEE. - 9781509028733 ; , s. 6346-6351
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Konferensbidrag (refereegranskat)abstract
- In this paper, we propose a glocal (global/local) control method for large-scale network systems. The objective of the glocal control here is to suppress global propagation of a disturbance injected at a local subsystem based on the integration of different types of controllers, called global and local controllers. For the design of global and local controllers, we construct an aggregated model and a truncated model that can, respectively, capture global average behavior and local subsystem behavior of the network system of interest. Based on state-space expansion, called hierarchical state-space expansion, we show that a cascade interconnection of the aggregated model and the truncated model can be seen as a low-dimensional approximate model of the original network system, which has good compatibility with independent design of the global and local controllers. Furthermore, we show that appropriate integration of the global and local controllers can improve control performance with respect to global propagation of local disturbance. Finally, the effectiveness of the proposed method is shown through a numerical example of a benchmark model representing the bulk power system in the eastern half of Japan.
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| 4. |
- van de Hoef, Sebastian, et al.
(författare)
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Efficient Dynamic Programming Solution to a Platoon Coordination Merge Problem With Stochastic Travel Times
- 2017
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Ingår i: IFAC-PapersOnLine. - : Elsevier. - 2405-8963. ; 50:1, s. 4228-4233
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Tidskriftsartikel (refereegranskat)abstract
- The problem of maximizing the probability of two trucks being coordinated to merge into a platoon on a highway is considered. Truck platooning is a promising technology that allows heavy vehicles to save fuel by driving with small automatically controlled inter-vehicle distances. In order to leverage the full potential of platooning, platoons can be formed dynamically en route by small adjustments to their speeds. However, in heavily used parts of the road network, travel times are subject to random disturbances originating from traffic, weather and other sources. We formulate this problem as a stochastic dynamic programming problem over a finite horizon, for which solutions can be computed using a backwards recursion. By exploiting the characteristics of the problem, we derive bounds on the set of states that have to be explored at every stage, which in turn reduces the complexity of computing the solution. Simulations suggest that the approach is applicable to realistic problem instances.
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| 5. |
- Wei, Jieqiang, et al.
(författare)
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Nonlinear consensus protocols with applications to quantized systems
- 2017
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Ingår i: IFAC PAPERSONLINE. - : ELSEVIER SCIENCE BV. - 2405-8963. ; , s. 15440-15445
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Konferensbidrag (refereegranskat)abstract
- This paper studies multi-agent systems with nonlinear consensus protocols, i.e., only nonlinear measurements of the states are available to agents. The solutions of these systems are understood in Filippov sense since the possible discontinuity of the nonlinear controllers. Under the condition that the nonlinear functions are monotonic increasing without any continuous constraints, asymptotic stability is derived for systems defines on both directed and undirected graphs. The results can be applied to quantized consensus which extend some existing results from undirected graphs to directed ones.
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