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Generation, Transmission and Distribution, IEE Proceedings-

Issue 4 • Date 8 July 2005

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Displaying Results 1 - 18 of 18
  • Evolutionary fuzzy control of flexible AC transmission system

    Page(s): 441 - 448
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (234 KB)  

    A fuzzy-controller design by the hybrid of genetic algorithm and particle-swarm optimisation (F-HGAPSO) is employed for a thyristor-controlled series capacitor (TCSC) to improve the transient stability of flexible AC transmission systems (FACTS). According to the variation of rotation speed, a fuzzy controller decides an approximate series capacitance to achieve a better dynamic response of FACTS. To design the fuzzy controller, a new design approach, the F-HGAPSO, is proposed. F-HGAPSO introduces the concept of the maturing phenomenon in nature into the evolution of individuals originally modelled by a genetic algorithm. The maturing phenomenon is mimicked by particle-swarm optimisation, where individuals enhance themselves based on social interactions and their private cognition. Simulations and comparisons with other approaches have demonstrated the effectiveness and efficiency of the proposed F-HGAPSO. View full abstract»

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  • Optimal decentralised design for output-feedback power system stabilisers

    Page(s): 449 - 459
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (230 KB)  

    An optimal decentralised design for output-feedback power-system stabilisers (PSSs) is presented. The PSS design problem is converted to an optimisation problem. A system dynamics-objective function is established and the derivations of an explicit expression for this function are given. Considerations for a stable system, the relative stability of low-frequency modes and the practical implementation of PSSs are all included in the constraints. Guidelines for choosing weighting factors affecting system performance are suggested. Only local and available state variables are adopted as the input signals of each PSS for the decentralised design. Output-feedback gains of the stabilisers can be obtained by using genetic algorithms. Structures of the designed PSSs are simple and easy to implement. The design process has considered different operating conditions. Three methods of assessment: eigenvalue analyses, time-domain simulations and total dynamic indices, are performed on a multimachine power system. Test results demonstrate the possibility of the proposed design applied to multimachine power systems to damp system oscillations. View full abstract»

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  • Composite auction method for suppressing unreasonable electricity price spikes in a competitive electricity market

    Page(s): 460 - 468
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (189 KB)  

    The existence of undesirable electricity price spikes in a competitive electricity market requires an efficient auction mechanism. However, many of the existing auction mechanism have difficulties in suppressing such unreasonable price spikes effectively. A new auction mechanism is proposed to suppress effectively unreasonable price spikes in a competitive electricity market. It optimally combines system marginal price auction and pay as bid auction mechanisms. A threshold value is determined to activate the switching between the marginal price auction and the proposed composite auction. Basically when the system marginal price is higher than the threshold value, the composite auction for high price electricity market is activated. The winning electricity sellers will sell their electricity at the system marginal price or their own bid prices, depending on their rights of being paid at the system marginal price and their offers' impact on suppressing undesirable price spikes. Such economic stimuli discourage sellers from practising economic and physical withholdings. Multiple price caps are proposed to regulate strong market power. We also compare other auction mechanisms to highlight the characteristics of the proposed one. Numerical simulation using the proposed auction mechanism is given to illustrate the procedure of this new auction mechanism. View full abstract»

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  • Normal form analysis of interactions among multiple SVC controllers in power systems

    Page(s): 469 - 474
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (194 KB)  

    The static var compensator (SVC) has been widely employed in power systems to provide reactive power and maintain busbar voltages. In the paper, a study case of negative interactions among multiple SVC controllers is reported, and an analytical approach based on normal form theory is proposed for the analysis of nonlinear interactions among the multiple SVC controllers in power systems. Also, a nonlinear interaction index is developed to investigate the interactions among multiple SVC controllers. The proposed approach has been applied to a typical IEEE 4-machine 11-busbar system. The simulation results validate the proposed approach. View full abstract»

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  • Ferroresonant oscillations in a transformer terminated line due to an energised parallel line on the same right-of-way

    Page(s): 475 - 482
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1154 KB)  

    Investigations carried out on ferroresonant oscillations in a transformer-terminated line due to an energised parallel line on the same right-of-way are reported. A nonlinear approach is used for analysis. The magnetic saturation characteristic of the individual phases of the three-phase transformer is represented and modelled by a polynomial. A topological technique is used to formulate the state space model to eliminate redundancy. Time domain simulations have been carried out using fourth-order Runge-Kutta method after corroboration with Microtran. The bifurcation diagram of the steady-state solutions is used to unearth the possible modes of ferroresonant oscillations and multiple solutions. The results reveal that with high saturation levels, chaotic ferroresonant oscillations are a distinct possibility due to the capacitive coupling between the parallel lines. Furthermore, the route to chaos is through a sequence of quasiperiodic oscillations. The sensitivities of the solutions with respect to the length of the de-energised line and the proximity between the parallel lines are analysed and discussed. View full abstract»

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  • Optimal spinning reserve allocation in deregulated power systems

    Page(s): 483 - 488
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (165 KB)  

    In a deregulated power system, spinning-reserve (SR) can be allocated to different ancillary service providers at different locations based on supplier bids and customer choices in terms of reliability and the related cost. The paper investigates the impacts of spinning-reserve allocations on system reliability and cost. A hybrid SR allocation method, which is based on cost-based SR allocation and risk based SR allocation, is proposed to determine the optimal SR locations. Implementation of these techniques in SR markets to determine the optimal SR schedules is presented. The IEEE Reliability Test System has been used to illustrate the proposed methods. View full abstract»

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  • Genetic k-means-algorithm-based classification of direct load-control curves

    Page(s): 489 - 495
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (199 KB)  

    To improve the load factors of a power system, direct load control (DLC) of air conditioners is one effective approach adopted by utilities. However, the performance of a DLC programme should be evaluated periodically to validate the preferential tariff provided to the customers involved. Prior to evaluating the performance, the DLC curves recorded should be categorised properly. The only further factor evaluated is the category of the DLC curves that comply with the required control pattern. Therefore, developing efficient approaches for classifying DLC curves is needed. In the paper, with the aim of reducing the number of variables for classification and enhancing the classification effectiveness, autoregression moving-averaging (ARMA) modelling techniques are employed to extract the features of the DLC curves. To ensure the adequacy of the ARMA models used for the DLC curves, the Akaike information criterion is assessed. Based on the features extracted, the genetic k-means algorithm is then adopted for classification owing to its ability to partition given global data optimally into a specified number of clusters. Through the proposed approaches, categories are derived of the DLC curves complying and noncomplying with the control pattern. The results obtained from the comparisons with the artificial-neural-network approach show that the clusters divided using the proposed approach exhibit very high classification rates for the practical data on Taiwan Power Company DLC programmes. View full abstract»

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  • Capacitor placement in large-sized radial distribution networks

    Page(s): 496 - 502
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (165 KB)  

    The capacitor-placement problem consists of finding specific locations to install capacitor banks in an electrical distribution network. Consequently, the losses are reduced due to the compensation of the reactive component of power flow. This problem can be formulated as a nonlinear mixed-integer optimisation model and its solution has represented a challenge for many optimisation methods in the past decades. This work proposes a new method, based on evolutionary algorithms, capable of solving large network instances that appear in real-world settings. Our evolutionary approach makes use of a memetic algorithm that employs a hierarchical organisation of the population in overlapping clusters. This structure leads to special selection and reproduction schemes, which improve the algorithm's overall performance. Computational tests were executed with two small-sized instances, usually utilised as a test set in previous works, and with two real large-sized distribution networks. Tests include a sensitivity analysis of the algorithm to the optimisation's critical parameters such as the energy cost, the maximum budget available to acquire and install the capacitors, and the amortization term of the investment. View full abstract»

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  • Optimisation of embedded generation sizing and siting by using a double trade-off method

    Page(s): 503 - 513
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (317 KB)  

    Distribution System Operators have the duty of managing the distribution system safely and efficiently. Distribution revenues are generally based on asset value but revenue systems based to some extent on network performance (e.g. on the level of losses or reliability) are becoming common in many countries. Thus the distribution planner has to maximise the profit of the investments for the system development and to improve the performance of the system as well. In many case the goals are conflicting and multiobjective planning criteria may be adopted to reduce network costs and investments and to maximise some specific performance (e.g. network reliability). Furthermore, with multiobjective programming the distribution planner has the possibility of choosing a trade-off solution in a set of acceptable solutions by applying criteria to minimise risks in uncertain scenarios. These features are particularly useful whether, according to the EU directive EU/2003/54, Embedded Generation (EG) and DSM are considered as possible planning alternatives to be compared with more traditional development actions in the search for the best solution to planning problems. In this context, a methodology is presented based on multiobjective programming and decision theory which helps the decision maker to find the best development plan for the system by using the EG as a development option and by explicitly managing risks and uncertainties. In particular, the proposed methodology solves the problem of maximising the network performance by optimising some power quality indicators, like voltage quality and harmonic distortion, and by minimising the network costs (e.g. energy losses or upgrade investments) with an optimised use of EG. For this reason, the problem of the optimal sizing and siting of EG has been reformulated as a constrained, multiobjective, and nondifferentiable optimisation problem. The main idea is to apply a double trade-off procedure: the first trade-off, by means of a multiobjective ε-constrained technique, allows a wide family of good EG siting and sizing solutions for all the scenarios considered (e.g. associated to a different set of wind speed at all the possible locations); the second one allows isolating the most robust solutions. In thi- s way the planner is completely free to drive the optimisation in a certain direction without loosing objectivity and generality. Simulation results obtained by using the proposed procedure on a test system demonstrate that alternatives disregarded by the decision theory application can result the most interesting ones. View full abstract»

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  • Novel reactive-power-compensation scheme for the Jeju-Haenam HVDC system

    Page(s): 514 - 520
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    The paper presents a new reactive-power-compensation scheme for the Jeju-Haenam HVDC system. Owing to changes in the Jeju AC power-system configuration since the Jeju-Haenam HVDC system was constructed, there is an increasing need to modify the existing reactive-power-compensation scheme. In the paper, a new reactive compensation scheme for the stable operation of the HVDC system has been proposed using integer programming to take into account the reactive power supply from new thermal power plants for the Jeju AC power system. An additional objective of the new compensation scheme to minimise the number of components switching in order to reduce temporary overvoltage. Nonlinear time-domain simulations using PSS/E and PSCAD/EMTDC were used to verify the proposed scheme. View full abstract»

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  • Performance study of two different compensating devices in a custom power park

    Page(s): 521 - 528
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (362 KB)  

    Simulation study of a custom power park (CPP) is presented. It is assumed that the park contains unbalanced and nonlinear loads in addition to a sensitive load. Two different types of compensators are used separately to protect the sensitive load against unbalance and distortion caused by the other loads. It has been shown that a shunt compensator can regulate the voltage of the CPP bus, whereas the series compensator can only regulate the sensitive load terminal voltage. Additional issues such as the load transfer through a static transfer switch, detection of sag/fault etc. are also discussed. The concepts are validated through PSCAD/EMTDC simulation studies on a sample distribution system. View full abstract»

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  • Digital control three-phase shunt active power filter with a new harmonic-current-extraction process

    Page(s): 529 - 538
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (599 KB)  

    Current harmonics are a major concern in three-phase diode bridge rectifiers with inductor or capacitor filters, and it is necessary to compensate for the harmonics that exist in the nonlinear load, in order to keep the utility supply current sinusoidal and free from undesired harmonics. Harmonic-current extraction is a prerequisite for its compensation; and in this paper, a signal-processing technique with an adaptive neural network (ADNN) is applied to determine the total harmonic current in a three-phase nonlinear load. The main feature of this proposed technique is that it can detect, not only the fundamental components of the load current, but also the different higher-order harmonic-current components. The proposed harmonic-extraction process also has a faster dynamic response as compared to the conventional Fourier transformation. The technique can detect the current harmonics in realtime, and its effectiveness is substantiated with a DSP-based experimental three-phase shunt active power filter. In the shunt-type active power filter, a three-phase voltage-source inverter, controlled by a deadbeat current controller, is used to generate the compensating current and make the supply current free from harmonic components. View full abstract»

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  • Fast non-recursive extraction of individual harmonics using artificial neural networks

    Page(s): 539 - 543
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (319 KB)  

    Non-linear loads, which cause harmonic distortion, are increasingly being used in electrical power systems. This is causing a major concern and real-time harmonic monitoring in electrical power systems has become important. Many applications such as harmonic monitoring and filter design need techniques for the fast extraction of individual harmonic components. The time limitations and computational complexity associated with conventional techniques make it appealing to investigate alternative techniques for harmonic extraction. A technique based on artificial neural networks (ANNs) for the fast extraction of individual harmonic components is presented. It uses the non-linear mapping capabilities of ANNs to accurately estimate the individual harmonic components of a distorted signal. The proposed algorithm is implemented on a real-time hardware platform and tested. Results show that the ANN-based harmonic extractor is significantly faster and less computationally complex than conventional techniques. View full abstract»

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  • Nonlinear co-ordinated control of excitation and governor for hydraulic power plants

    Page(s): 544 - 548
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (176 KB)  

    A nonlinear decentralised excitation and governor co-ordinated controller design for hydraulic power plants is proposed to enhance power system transient stability. First, the excitation system and hydro-governor system, considering non-elastic water hammer effect, is modelled as a whole. Then, based on differential geometric theory, the original nonlinear system for multi-machines is exactly linearised by appropriate co-ordinate transformation. After that, linear optimisation control is applied such that the final optimised nonlinear excitation and governor co-ordinated control law can be obtained. To demonstrate the efficiency and analyse the co-ordination mechanism of the proposed controller, simulations on an OMIB system and the EPRI-36 system are performed. Comparison with classical excitation and governor control, nonlinear optimal excitation control, nonlinear robust governor control, the suggested decentralised and co-ordinated control can achieve considerably better performance in improving the transient stability of power systems. View full abstract»

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  • Systematic short-circuit-analysis method for unbalanced distribution systems

    Page(s): 549 - 555
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (210 KB)  

    A systematic short-circuit-analysis method for unbalanced distribution systems is proposed. The proposed method employs the actual three-phase models to handle unsymmetrical faults. Two matrices developed from the topological structures of distribution systems are used to analyse the variations of bus voltages, bus-current injections and branch currents under fault conditions. A short-circuit-analysis method can then be developed from these two matrices and be used to solve the various types of single or simultaneous unsymmetrical faults. Since the proposed method does not use the traditional admittance matrix, the time-consuming procedures such as tri-factorisation or inverse of admittance matrix are not necessary; therefore, the proposed method can achieve the advantages of high speed, robust convergence and improved accuracy with lower memory requirements. Test results show that the proposed method is systematic, efficient, accurate and easily programmable. View full abstract»

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  • Fast-individual-harmonic-extraction technique

    Page(s): 556 - 562
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (537 KB)  

    Harmonic distortion in power networks is continuously increasing owing to the increased use of nonlinear loads in power-distribution networks. Consequently, harmonic monitoring and control are becoming particularly important for both utilities and consumers to reduce their harmful effects. In some applications, such as real-time harmonic monitoring and active filters, techniques for fast extraction of individual harmonic components are required. The relatively long response time of conventional techniques make them less appealing when the speed of response is important. The paper deals with the problem of individual-harmonic extraction for the purpose of harmonic filtering and compensation. A common problem associated with existing individual-harmonic-extraction techniques is the speed of extracting a single harmonic component, which determines the response of the compensator. Standard harmonic-extraction techniques are investigated and a new fast-individual-harmonic-extraction (FIHE) technique is proposed. It is shown that the proposed FIHE is capable of performing harmonic extraction six times faster than the Fourier transform and provides better filtering characteristics than traditional filters such as Butterworth and FIR filters. Computer simulation and laboratory experimental results are provided to illustrate the characteristics and performance of the proposed technique. View full abstract»

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  • Unit commitment by a tabu-search-based hybrid-optimisation technique

    Page(s): 563 - 574
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    The paper introduces an application of hybrid-particle-swarm optimisation and sequential-quadratic-programming technique (hybrid PSO-SQP) guiding the tabu search (TS) method for solving the unit-commitment (UC) problem. The UC problem is divided into a combinatorial subproblem in unit-status variables and a nonlinear-programming subproblem in unit-power-output variables. TS a powerful heuristic method that uses the history of the search. It has proved to be a successful strategy for combinatorial-optimisation problems. The central idea of the TS method is the use of adaptive memory, which prevents convergence to local optima, by driving the search to different parts of the search space. The TS method with an improved random-perturbation-of-current-solution scheme is proposed to solve the combinatorial subproblem. A simple scheme for generating the initial feasible commitment schedule for the TS method is also proposed. The nonlinear programming subproblem is solved using the hybrid PSO-SQP technique. A practical system, Neyveli thermal-power-station (NTPS), India, and several example systems were studied to validate the robustness and effectiveness of the proposed technique for the UC problem. View full abstract»

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  • Continuation of local bifurcations for power system differential-algebraic equation stability model

    Page(s): 575 - 580
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (199 KB)  

    Information about the boundary of local bifurcations is important for utilities to guarantee the secure operation of power systems, and therefore local bifurcation analysis is a useful tool in power systems stability analysis. A new method is presented for calculating the multi-parameter singularity-induced, saddle-node and Hopf bifurcation boundary associated with the parameter-dependent differential-algebraic equations (DAE), which are used to model power systems dynamics. This method is based on the idea of the continuation method, which means that these three kinds of local bifurcations of DAE systems are expressed by appropriate nonlinear algebraic equations, which can be used to track the multi-parameter local bifurcation boundary directly by the continuation method from a known one-parameter local bifurcation point on the boundary, and thus it has the advantage of being a direct method as the continuation method itself inherently contains an iteration procedure during tracking the boundary point by point. Another advantage of this method is that it keeps the DAE form of the mathematical model of power systems and thus preserves the sparsity of the data structure. Several example power systems are used to illustrate the proposed method. View full abstract»

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