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Online ISSN 1752-1424 Print ISSN 1752-1416

IET Renewable Power Generation

Volume 6, Issue 5, September 2012

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Volume 6, Issue 5

September 2012

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    • Operating point of islanded microgrids consisting of conventional doubly fed induction generators and distributed supporting units
      • Author(s): G. Díaz ; C. González-Morán ; C. Viescas
      • Source: IET Renewable Power Generation, Volume 6, Issue 5, p. 303 –314
      • DOI:  10.1049/iet-rpg.2011.0148
      • Type: Article
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      • p. 303 –314 (12)
        This study presents a comprehensive formulation to represent islanded microgrids, where the base power is obtained from wind energy (doubly fed induction generators), and the ancillary services and energy buffering are obtained from distributed resources, either distributed generation or energy storage. Furthermore, this study presents an approach to solve the operational constraints (pitch regulation, power limits, etc.) by transforming the problem into a variational inequality problem. This eventually leads to a constrained version of the original unconstrained problem that preserves its solvability as if it was an unconstrained problem; of special interest because, as shown in the study, the errors of not considering the operational constraints may be large. The formulation presented is of interest for finding the operating point of such a microgrid, and to directly represent the equality constraints that limit the feasibility set of the optimisation problems.
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      Measuring the volatility of wholesale electricity prices caused by wind power uncertainty with a correlation model
      • Author(s): Y. Wei ; F. Li ; K. Tomsovic
      • Source: IET Renewable Power Generation, Volume 6, Issue 5, p. 315 –323
      • DOI:  10.1049/iet-rpg.2011.0093
      • Type: Article
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      • p. 315 –323 (9)
        There is an increasing need to understand the impact of high-penetration wind power on various aspects of power system operation. This study presents a methodology to evaluate the impact of market price volatility on intermittent wind power. The proposed methodology first considers the uncertainty of wind power using a probabilistic distribution of wind speed in combination with the rated speed–MW curve. The correlation among different wind power plants is also modelled. With these statistical models, a Monte Carlo simulation (MCS) approach can be used to assess the probabilistic distribution of the price signals, that is, the probabilistic locational marginal pricing (LMP) distribution. Since the computational effort of MCS is intensive, a lookup table is proposed as preprocessing to greatly simplify the MCS. The proposed approach is tested with the PJM 5-bus system and the IEEE 118-bus system. Rules of thumb are drawn regarding the probabilistically calculated LMP and the correlation coefficients.
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      Feedback linearisation oriented approach to Q–V control of grid connected photovoltaic units
      • Author(s): F. Delfino ; G.B. Denegri ; M. Invernizzi ; R. Procopio
      • Source: IET Renewable Power Generation, Volume 6, Issue 5, p. 324 –339
      • DOI:  10.1049/iet-rpg.2011.0075
      • Type: Article
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      • p. 324 –339 (16)
        This study proposes a new control scheme to manage active and reactive power injections into the distribution grids provided by photovoltaic (PV) generating units. Such scheme is derived by resorting to the so-called ‘feedback linearisation’ theory, which relies on the central concept to algebraically transform non-linear systems dynamics into fully or partly linear ones, so that linear control techniques can be applied. To do this, a suitable state transformation is required, in order to simplify the form of the power system to be controlled. The developed scheme receives as input the reference signal for the PV unit voltage (generated by a maximum power point tracker controller) and the one for the desired reactive power and produces as output the modulating signal of the grid interface pulse width modulation inverter. A detailed simulation campaign on a medium voltage grid connected PV power plant is performed in the PSCAD-EMTDC electromagnetic environment, in order to verify the effectiveness of the proposed control algorithm and to highlight its main advantages with respect to traditional regulation methodologies.
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      Fuzzy adaptive Kalman filter for wind power output smoothing with battery energy storage system
      • Author(s): X. Li
      • Source: IET Renewable Power Generation, Volume 6, Issue 5, p. 340 –347
      • DOI:  10.1049/iet-rpg.2011.0177
      • Type: Article
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      • p. 340 –347 (8)
        The energy storage system (ESS) is the current, widely popular means of smoothing intermittent wind power (WP) generation to regulate output power uncertainty in a wind power generation system (WPGS). This study presents a novel Kalman filter (KF) application method for smoothing the power-output fluctuation of a WPGS based on a battery energy storage system (BESS). A fuzzy logic control method was added to a first-order KF with feedback control of the battery state of charge (SOC). On this basis, the smoothing power output of the hybrid wind/battery power system could be adaptively regulated based on the SOC, and consequently, the battery SOC could be effectively managed according to the charge- and WP-output levels. The effectiveness of the proposed control strategy based on the fuzzy adaptive KF was verified using MATLAB/SIMULINK software and simulation tests.
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      Evaluation of the mainstream wind turbine concepts considering their reliabilities
      • Author(s): Q. Gao ; C. Liu ; B. Xie ; X. Cai
      • Source: IET Renewable Power Generation, Volume 6, Issue 5, p. 348 –357
      • DOI:  10.1049/iet-rpg.2011.0201
      • Type: Article
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      • p. 348 –357 (10)
        Wind turbine technologies have reached such a stage that the power rating of a single unit installed for grid connection has well exceeded MW level, and this trend is still developing. Some previous work has been carried out by researchers to compare different wind turbine concepts, but most of these comparisons assume ideal operating conditions. In this paper, an economic evaluation of the mainstream wind turbine concepts rated at 5 MW for onshore sites by taking into account their reliabilities is made. Also not only the low-voltage designs but also medium voltage designs are presented. The comparison results suggest that the direct drive wind turbines produce the highest annual energy, but the doubly fed induction generator typed wind turbines still appear the most economic at this power rating.
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      Eco-design optimisation of an autonomous hybrid wind–photovoltaic system with battery storage
      • Author(s): D. Abbes ; A. Martinez ; G. Champenois
      • Source: IET Renewable Power Generation, Volume 6, Issue 5, p. 358 –371
      • DOI:  10.1049/iet-rpg.2011.0204
      • Type: Article
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      • p. 358 –371 (14)
        In this study, a new approach to design an autonomous hybrid wind–photovoltaic (PV)-batteries system is presented in order to assist the designers to take into consideration both the economic and ecological aspects. Primary embodied energy (EE) has been introduced as a new criterion for hybrid systems, designing with the objective to minimise loss of power supply probability (LPSP). For a location, meteorological and load data have been collected and assessed. Then, modelling and primary energy analysis have been achieved for all components of the hybrid system. Finally, an optimal configuration has been carried out using a dynamic model and applying two different algorithms with single and multi-objective optimisation. The methodology has been performed successfully for the sizing of a wind–PV-batteries system to supply at least 95% of the yearly total electric demand of a residential house. The simulation results show that the optimal configuration meets the desired system reliability requirements (LPSP <5%) with the lowest EE. A life cycle cost analysis has been established at the end of the study to demonstrate the importance of economic considerations.
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