A simple maximum power point tracking based control strategy applied to a variable speed squirrel cage induction generator

This paper presents a comprehensive modelling and control study of a variable speed wind energy conversion system based on a squirrel-cage induction generator (SCIG). The mathematical model of the SCIG is derived in Park frame along with the indirect field oriented control (IFOC) scheme based on a proportional and integral speed controller. A simple maximum power point tracking strategy is used to determine the optimal speed under variable wind speed conditions which is then used as the reference in the IFOC scheme. Power flow between the supply and the inverter is regulated via simultaneous control of the active and reactive currents of the grid and the DC link voltage. The simulation results show that the proposed control technique is able to maximise the energy extracted from the wind during the simulation scenarios considered. The results also demonstrate good transient response characteristics in the decoupled real and reactive powers.Peer reviewedFinal Accepted Versio

Harnessing high altitude solar power

As an intermediate solution between Glaser's satellite solar power (SSP) and ground-based photovoltaic (PV) panels, this paper examines the collection of solar energy using a high-altitude aerostatic platform. A procedure to calculate the irradiance in the medium/high troposphere, based on experimental data, is described. The results show that here a PV system could collect about four to six times the energy collected by a typical U.K.-based ground installation, and between one-third and half of the total energy the same system would collect if supported by a geostationary satellite (SSP). The concept of the aerostat for solar power generation is then briefly described together with the equations that link its main engineering parameters/variables. A preliminary sizing of a facility stationed at 6 km altitude and its costing, based on realistic values of the input engineering parameters, is then presented

Feasibility studies of a converter-free grid-connected offshore hydrostatic wind turbine

Owing to the increasing penetration of renewable power generation, the modern power system faces great challenges in frequency regulations and reduced system inertia. Hence, renewable energy is expected to take over part of the frequency regulation responsibilities from the gas or hydro plants and contribute to the system inertia. In this article, we investigate the feasibility of frequency regulation by the offshore hydrostatic wind turbine (HWT). The simulation model is transformed from NREL (National Renewable Energy Laboratory) 5-MW gearbox-equipped wind turbine model within FAST (fatigue, aerodynamics, structures, and turbulence) code. With proposed coordinated control scheme and the hydrostatic transmission configuration of the HWT, the `continuously variable gearbox ratio' in turbulent wind conditions can be realised to maintain the constant generator speed, so that the HWT can be connected to the grid without power converters in-between. To test the performances of the control scheme, the HWT is connected to a 5-bus grid model and operates with different frequency events. The simulation results indicate that the proposed control scheme is a promising solution for offshore HWT to participated in frequency response in the modern power system

Integration of renewable energy sources in the distribution network

Tato práce uvádí obecné informace o obnovitelných zdrojích energie, typech elektráren a jejich pracovních principech. Práce je zaměřena na větrné elektrárny (principy, typy, komponenty, výhody a nevýhody). Obsahuje také pravidla pro připojování rozptýlených zdrojů energie k distribuční soustavě. V praktické části je řešena případová studie, která demonstruje napěťové charakteristiky pro síť vysokého napětí před a po připojení větrné elektrárny do distribuční sítě se dvěma různými hodnotami účiníku.This thesis will provide general information about renewable energy sources, types of power plants and their working principles. The thesis is focused on wind power plants (principles, types, components, advantages and disadvantages). It also includes the rules for connecting dispersed energy sources to the distribution system. In practical part, a case study demonstrates voltage characteristics before and after connection of a wind power plant to a distribution network with two different values of power factor

Torque analysis on a double rotor electrical variable transmission with hybrid excitation

An electrical variable transmission (EVT) can be used as a power splitting device in hybrid electrical vehicles. The EVT analyzed in this paper is a rotating field electrical machine having two concentric rotors. On the outer rotor, permanent magnets (PMs) are combined with a dc-field winding, being the first implementation of its kind. The magnetic field in the machine as well as the electromagnetic torque on both rotors are a function of the q- and d-axis currents of the stator and inner rotor, as well as the dc-field current. To describe and fully understand this multiple-input multiple-output machine, this paper gives an overview of the influence of the different current inputs on the flux linkage and torque on both rotors. Focus is given to the hybrid excitation in the d-axis by combining the dc-field current and the alternating currents. This has the advantage compared to other EVT topologies that unwanted stator torque can be avoided without stator d-axis current flux weakening. Results of the analysis are presented by means of the torque to current characteristics of a double rotor PM-assisted EVT, as well as the torque to current ratios. The machine characteristics are finally experimentally verified on a prototype machine

Analysis of a stand-alone hydraulic offshore wind turbine coupled to a pumped water storage facility

The concept of wind turbines operating with hydraulic transmissions is gaining popularity. With the promise of improved energy density and lower maintenance costs, a number of manufacturers are evaluating such a novel concept. In the current study an offshore-specific hydraulic wind turbine design is proposed. This is based on the use seawater as the working fluid in a large scale, open-loop transmission system. The possibility of coupling such a system to an onshore pressurized water storage facility is also evaluated. Simulation results indicate the potential for such an energy storage system, to address a supply-demand mismatch without requiring intermediate conversion to electricity, as in current pumped storage facilities used in conjunction with wind turbines.Alternative Technologies Ltd., Energy Investment Ltd, JMV Vibro Blocks Ltd., Solar Engineering Ltd. and Solar Solutions Ltd.peer-reviewe