Online ISSN
1752-1424
Print ISSN
1752-1416
IET Renewable Power Generation
Volume 4, Issue 4, July 2010
Volumes & issues:
Volume 4, Issue 4
July 2010
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- Author(s): S.O. Faried ; R. Billinton ; S. Aboreshaid
- Source: IET Renewable Power Generation, Volume 4, Issue 4, p. 299 –307
- DOI: 10.1049/iet-rpg.2009.0031
- Type: Article
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p.
299
–307
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This study presents a stochastic-based approach to evaluate the probabilistic transient stability indices of a power system incorporating wind farms (WFs). In this context, investigations have been conducted on a hypothetical test system representing a typical power system taking into consideration the uncertainties of the factors associated with the practical operation of a power system, namely fault type, fault location, fault impedance, fault clearing process, system parameters and operating conditions and high-speed reclosing process. The effects of the WF sizes and locations on the overall system stability have been investigated. Moreover, this study presents stochastic models for the wind turbine as well as the spring constant of the reduced two-mass shaft model of the wind generator. The time-domain simulations are obtained using the electro-magnetic transient programme. - Author(s): H.T. Ma and B.H. Chowdhury
- Source: IET Renewable Power Generation, Volume 4, Issue 4, p. 308 –316
- DOI: 10.1049/iet-rpg.2009.0100
- Type: Article
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p.
308
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A pitch angle controller and a rotor speed controller are proposed for wind plant output active power adjustment. Combining the turbine inertial control with pitch angle control provides a better outlook for long-term control. The control schemes are developed for wind generators to equip them with the capability to participate in restoring grid frequency after a disturbance. With the proposed controllers, the wind plant has a higher flexibility to operate more like a synchronous generator and is able to output either larger or smaller amounts of power as required so as to contribute to grid frequency restoration. The controllers are tested on a four-bus test system for verification of the grid frequency performance under varying system dynamic conditions. - Author(s): L. Piegari and R. Rizzo
- Source: IET Renewable Power Generation, Volume 4, Issue 4, p. 317 –328
- DOI: 10.1049/iet-rpg.2009.0006
- Type: Article
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p.
317
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The optimisation of energy generation in a photovoltaic (PV) system is necessary to let the PV cells operate at the maximum power point (MPP) corresponding to the maximum efficiency. Since the MPP varies, based on the irradiation and cell temperature, appropriate algorithms must be utilised to track the MPP. This is known as maximum power point tracking (MPPT). Different MPPT algorithms, each with its own specific performance, have been proposed in the literature. A so-called perturb and observe (P&O) method is considered here. This method is widely diffused because of its low-cost and ease of implementation. When atmospheric conditions are constant or change slowly, the P&O method oscillates close to MPP. However, when these change rapidly, this method fails to track MPP and gives rise to a waste of part of the available energy. An adaptive P&O method is proposed in this study that has faster dynamics and improved stability compared to the traditional P&O. The MPPT algorithm was set up and validated by means of numerical simulations and experimental tests, confirming the effectiveness of the method. - Author(s): F. Delfino ; R. Procopio ; M. Rossi ; G. Ronda
- Source: IET Renewable Power Generation, Volume 4, Issue 4, p. 329 –340
- DOI: 10.1049/iet-rpg.2009.0134
- Type: Article
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p.
329
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This study addresses the issue of the control of both active (P) and reactive (Q) power flows injected by grid connected photovoltaic (PV) units participating in the provision of the reactive power compensation ancillary service. A model is derived allowing to define a sort of ‘capability chart’ for the PV unit, that is, the set of points in the P–Q plane which, at steady state, can be reached by properly operating the control system and without exceeding the physical limits of all the involved devices. To this aim, a basic algorithm is developed in the MATLAB environment relying on a simplified description of the system, which neglects the harmonics injected by the voltage source converter inverter used to connect the PV unit with a medium voltage radial distribution grid. The proposed model is used to evaluate all the possible working points in the P–Q chart; a proof of the stability of those points, using the well-known Lyapunov methods, is also annexed. Finally, simulations with the electromagnetic code PSCAD–EMTDC are performed in order to assess the validity of the approximate results and to improve the developed basic algorithm. - Author(s): G. Todeschini and A.E. Emanuel
- Source: IET Renewable Power Generation, Volume 4, Issue 4, p. 341 –353
- DOI: 10.1049/iet-rpg.2009.0147
- Type: Article
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This work deals with the steady-state operation of wind energy conversion systems (WECSs) used simultaneously as active filters (AFs) and power generators. This application is motivated by the increasing number of non-linear loads (NLLs) on the power grid and by the possibility to offer an economical alternative to the installation of dedicated filters that sink the harmonic currents injected by such loads. The main contributions of this paper are as follows: (i) three different control systems that allow the simultaneous use of the WECS as AF and power generator are presented; (ii) compensation of triplen harmonics is addressed; (iii) additional power losses due to AF operation, leading to the derating of the WECS, are quantified; (iv) results based on numerical simulations are provided. - Author(s): E. Karatepe ; Syafaruddin ; T. Hiyama
- Source: IET Renewable Power Generation, Volume 4, Issue 4, p. 354 –368
- DOI: 10.1049/iet-rpg.2009.0150
- Type: Article
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p.
354
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The interest in improving the efficiency of photovoltaic (PV) system has emerged because of increasing the number of home-based or small-scale PV power system. However, the home-based PV system is vulnerable to the non-uniform operating conditions. Under such circumstances, multiple-local maximum power points (MPPs) occur on the power–voltage characteristics and an advanced control algorithm is required to track the global MPP. It is very difficult to provide a sophisticated control algorithm because of the non-linear characteristics of PV system. This study describes the potential to improve the efficiency of PV arrays under non-uniform operating conditions by using the conventional hill-climbing MPP tracking method in total cross tied (TCT) connected PV arrays, in which each group of series connected solar cells that belong to single bypass diode is interconnected. The various scenarios were tested and the results indicate that the efficiency of the proposed system is much higher than that of the same size of series–parallel (SP) PV array configuration. - Author(s): A.J. Roscoe and G. Ault
- Source: IET Renewable Power Generation, Volume 4, Issue 4, p. 369 –382
- DOI: 10.1049/iet-rpg.2009.0212
- Type: Article
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p.
369
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The rollout of smart meters raises the prospect that domestic customer electrical demand can be responsive to changes in supply capacity. Such responsive demand will become increasingly relevant in electrical power systems, as the proportion of weather-dependent renewable generation increases, due to the difficulty and expense of storing electrical energy. One method of providing response is to allow direct control of customer devices by network operators, as in the UK ‘Economy 7’ and ‘White Meter’ schemes used to control domestic electrical heating. However, such direct control is much less acceptable for loads such as washing machines, lighting and televisions. This study instead examines the use of real-time pricing of electricity in the domestic sector. This allows customers to be flexible but, importantly, to retain overall control. A simulation methodology for highlighting the potential effects of, and possible problems with, a national implementation of real-time pricing in the UK domestic electricity market is presented. This is done by disaggregating domestic load profiles and then simulating price-based elastic and load-shifting responses. Analysis of a future UK scenario with 15 GW wind penetration shows that during low-wind events, UK peak demand could be reduced by 8–11 GW. This could remove the requirement for 8–11 GW of standby generation with a capital cost of £2.6 to £3.6 billion. Recommended further work is the investigation of improved demand-forecasting and the price-setting strategies. This is a fine balance between giving customers access to plentiful, cheap energy when it is available, but increasing prices just enough to reduce demand to meet the supply capacity when this capacity is limited. - Author(s): S. Hazra and P.S. Sensarma
- Source: IET Renewable Power Generation, Volume 4, Issue 4, p. 383 –393
- DOI: 10.1049/iet-rpg.2008.0102
- Type: Article
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p.
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This study presents a rugged and cost-effective scheme for start-up and operation of a stand-alone squirrel cage induction machine (SCIG) for a wind energy conversion system (WECS). A voltage source converter (VSC) directly interfaces the SCIG with an equivalent dc load network, which could also be the DC link of an inverter. The VSC dc bus is supported by an electrolytic capacitor and the proposed scheme ensures reliable start up with these rudimentary components. The dc bus voltage is ramped to the rated value from a small initial voltage produced by remanent magnetism of the SCIG core. Subsequently, the load is applied. The V/f control paradigm for motoring operation is suitably extended to the SCIG for controlling both voltage build-up and dynamic transients. A controller is specifically designed to maintain constant dc bus voltage under wind speed and electrical load variations. Steady-state machine flux is maintained constant up to the base speed, which maximises machine utilisation and power extraction especially at higher wind speeds. The overall system modelling and analytical control design is presented. The proposed control strategy has been validated through simulation and experimentally verified on a low power (2.2 kW) laboratory prototype.
Probabilistic evaluation of transient stability of a power system incorporating wind farms
Working towards frequency regulation with wind plants: combined control approaches
Adaptive perturb and observe algorithm for photovoltaic maximum power point tracking
Integration of large-size photovoltaic systems into the distribution grids: a P–Q chart approach to assess reactive support capability
Wind energy conversion systems as active filters: design and comparison of three control methods
Simple and high-efficiency photovoltaic system under non-uniform operating conditions
Supporting high penetrations of renewable generation via implementation of real-time electricity pricing and demand response
Self-excitation and control of an induction generator in a stand-alone wind energy conversion system
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