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Online ISSN 1751-8695 Print ISSN 1751-8687

IET Generation, Transmission & Distribution

Volume 4, Issue 8, August 2010

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Volume 4, Issue 8

August 2010

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    • Robust and coordinated tuning of power system stabiliser gains using sequential linear programming
      • Author(s): R.A. Jabr ; B.C. Pal ; N. Martins ; J.C.R. Ferraz
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 8, p. 893 –904
      • DOI:  10.1049/iet-gtd.2009.0669
      • Type: Article
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      • p. 893 –904 (12)
        This study presents a linear programming (LP)-based multivariable root locus following technique for coordinating the gain settings of power system stabilisers (PSSs). The stabiliser robustness is accounted for in the design problem by simultaneously considering the state-space representations and multivariable root loci corresponding to different operating scenarios. The proposed technique computes a curve in the PSS gain parameter space such that when the PSS gains move along this curve to their optimal values, the branches of the corresponding multivariable root loci terminate at satisfactory points in the complex plane. The curve in the gain parameter space is computed via a linear program that successively minimises the Euclidean distance between the unsatisfactory and satisfactory eigenvalue locations. The design method is demonstrated on a 39-bus test system with 14 operating scenarios. A comparison is carried out between the coordination results of two PSS structures, one involving two phase-lead blocks and the other comprised of two phase-lead blocks and a phase-lag block.
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      Design and analysis of active power control strategies for distributed generation inverters under unbalanced grid faults
      • Author(s): F. Wang ; J.L. Duarte ; M.A.M. Hendrix
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 8, p. 905 –916
      • DOI:  10.1049/iet-gtd.2009.0607
      • Type: Article
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      • p. 905 –916 (12)
        Distributed power generation systems are expected to deliver active power into the grid and support it without interruption during unbalanced grid faults. Aiming to provide grid-interfacing inverters the flexibility to adapt to the coming change of grid requirements, an optimised active power control strategy is proposed to operate under grid faults. Specifically, through an adjustable parameter it is possible to change the relative amplitudes of oscillating active and reactive power smoothly, while simultaneously eliminating the second-order active or reactive power ripple at the two extremes of the parameter range. The steering possibility of the proposed strategy enables distributed generation inverters to be optimally designed from the perspectives of both the power-electronic converters and the power system. The proposed strategy is proved through simulation and further validated by experimental results.
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      Option-game-based method for generation investment analysis considering uncertain carbon reduction policy in the electricity market
      • Author(s): G. Liu ; J.H. Zhao ; F. Wen ; X. Yin ; Z.Y. Dong
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 8, p. 917 –927
      • DOI:  10.1049/iet-gtd.2009.0439
      • Type: Article
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      • p. 917 –927 (11)
        Greenhouse gas, especially CO2, emissions impact on global climate has been widely recognised. Emissions reduction has become an important issue. Efforts have been made globally in establishing emission policies and protocols. However, considering the fact that different countries have different carbon reduction schemes, and significant variations are still possible for existing schemas, future CO2 prices can be highly uncertain. The power generation sector will be significantly affected by changing policies and therefore significant uncertainties will be involved in the operation and investment processes. Moreover, investments in thermal power plants are also influenced by many other uncertain factors such as fuel prices, spot electricity prices and the investment behaviours of rival generation companies. An appropriate method is urgently needed to model these uncertainties in the investment process. A novel framework of generation investment decision-making is proposed herewith. The option game theory is employed to handle multiple uncertain factors. The investment decision making will be solved with a Barraquand–Martineau option pricing model-based method. Case studies are conducted to assess the performance of the proposed framework.
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      Mixed integer non-linear programming via the cross-entropy approach for power system stabilisers location and tuning
      • Author(s): K. Sebaa ; H. Guéguen ; M. Boudour
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 8, p. 928 –939
      • DOI:  10.1049/iet-gtd.2009.0435
      • Type: Article
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      • p. 928 –939 (12)
        Mixed integer non-linear programming (MINLP) via the cross-entropy approach for the optimal location and tuning of power system stabiliser (PSS) is presented. The considered problem is to maximise the damping ratio of the global system under a minimum number of PSS and simultaneously to find out the best candidate machines to be equipped with PSSs. The damping ratio objective is achieved by tuning the controllers to shift the lightly damped and undamped electromechanical modes of all plants to a prescribed zone in the s-plane. This problem of tuning and location of PSS over a wide range of system configurations is formulated as a MINLP problem where the objective is the aggregation of the two objectives on the damping ratio and on the PSS's number. The mixed optimisation problem, with a great combinatory aspect, is solved by an extension of the cross-entropy approach from the rare event framework. The performance of this technique for damping the oscillations in multimachine power systems is confirmed through eigenvalues analysis over many scenarios. For comparative purpose the Monte Carlo simulation and the classical approach have been used to show the effectiveness of the proposed approach.
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      Generation expansion planning in wind-thermal power systems
      • Author(s): S. Kamalinia  and  M. Shahidehpour
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 8, p. 940 –951
      • DOI:  10.1049/iet-gtd.2009.0695
      • Type: Article
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      • p. 940 –951 (12)
        The intermittency and volatility of wind generation (WG) would require additional upward and downward reserves, as well as enhanced ramping capabilities in power systems. This study investigates the optimal expansion planning of fast-response generating capacity (e.g. gas-fired units) to accommodate the uncertainty of WG. The study utilises a mixed integer programming-based security-constrained unit commitment for analysing operational and reliability issues related to the proposed optimisation problem. Numerical experiments signify the effectiveness of the proposed method.
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      Fold back current control and admittance protection scheme for a distribution network containing distributed generators
      • Author(s): M. Dewadasa ; A. Ghosh ; G. Ledwich
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 8, p. 952 –962
      • DOI:  10.1049/iet-gtd.2009.0614
      • Type: Article
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      • p. 952 –962 (11)
        Islanded operation, protection, reclosing and arc extinguishing are some of the challenging issues related to the connection of converter interfaced distributed generators (DGs) into a distribution network. The isolation of upstream faults in grid-connected mode and fault detection in islanded mode using overcurrent devices are difficult. In the event of an arc fault, all DGs must be disconnected in order to extinguish the arc. Otherwise, they will continue to feed the fault, thus sustaining the arc. However, the system reliability can be increased by maximising the DG connectivity to the system; therefore the system protection scheme must ensure that only the faulted segment is removed from the feeder. This is true even in the case of a radial feeder as the DG can be connected at various points along the feeder. In this paper, a new relay scheme is proposed which, along with a novel current control strategy for converter interfaced DGs, can isolate permanent and temporary arc faults. The proposed protection and control scheme can even coordinate with reclosers. The results are validated through PSCAD/EMTDC simulation and MATLAB calculations.
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      Reactive power dispatch and planning using a non-linear branch-and-bound algorithm
      • Author(s): C.R.N. Estevam ; M.J. Rider ; E. Amorim ; J.R.S. Mantovani
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 8, p. 963 –973
      • DOI:  10.1049/iet-gtd.2009.0422
      • Type: Article
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      • p. 963 –973 (11)
        This study proposes the use of a non-linear branch-and-bound (B&B) algorithm to solve the reactive power dispatch and planning problem of an electrical power system. The problem is formulated as a mixed integer non-linear programming (MINLP) problem. The MINLP is relaxed resulting in a set of non-linear programming (NLP) problems, which are solved at each node of the B&B tree through a primal dual-interior point algorithm. The non-linear B&B algorithm proposed has special fathoming criteria to deal with non-linear and multimodal optimisation models. The fathoming tests are redefined, adding a safety margin value to the objective function of each NLP problem before they are fathomed through the objective function criteria, avoiding convergence to local optimum solutions. The results are presented using three test systems from the specialised literature. The B&B algorithm found several optimum local solutions and the best solution was found after solving some NLP problems, with little computational effort.
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      Multi-objective feeder reconfiguration in different tariff structures
      • Author(s): D. Singh  and  R.K. Misra
      • Source: IET Generation, Transmission & Distribution, Volume 4, Issue 8, p. 974 –988
      • DOI:  10.1049/iet-gtd.2010.0128
      • Type: Article
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      • p. 974 –988 (15)
        The operational cost of an in-house distribution system (IDS) has been formulated as a multi-objective function to minimise the overall cost of MW, Mvar and MVA intakes. The reconfiguration investigations have been carried out considering different load types and a comparison is made with the commonly assumed constant load type used in such studies. Different tariff situations are simulated on 33-node test systems. The results obtained establish that load type is a major deciding factor in reconfiguration and cannot be represented by constant load models as used in such studies in case of IDS.
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