The interaction of the dynamics of doubly fed wind generators with the electromechanical mode of nearby synchronous generators (SGs) can affect the small signal stability of power systems with high penetration levels of wind power. In this study, a novel approach is developed to investigate these interactions and their impact on the damping of power system oscillations. In this approach it is not necessary to model the dynamic behaviour of system SGs and only the frequencies of system oscillations are important. This approach is based on the sensitivity of SGs electromechanical eigenvalue with respect to variations in the Jacobian matrix of power system. By applying this approach to a test system, two of the wind farm (WF) modes are identified to have interaction with the SG electromechanical mode, one has detrimental and the other has beneficial impact, which decrease the damping of system electromechanical oscillation altogether. By using the modal analysis technique, the WF controller gains are retuned to shift the detrimental and beneficial interacting modes away and towards the frequency of system oscillation, respectively. It is shown that this results in the improvement of system oscillation damping whereas the dynamic performance of WF remains satisfactory.

In this paper, a low-power, direct-drive, double-sided linear switched reluctance generator (LSRG) is designed and constructed as one of the components of generator matrix for wave power utilizations by direct energy conversion. This machine has the characteristics of simple construction, mechanical robustness, and maintenance free. Following the theoretical background of linear power generation, characteristic investigation is performed by finite element analysis, which shows that each phase can be controlled individually and normal forces can be approximately counteracted from the double-sided structure. Both preliminary power simulation and experimental results show that there is an optimized generation region for turn-on and turn-off position control strategy. The closed loop test based on Pulse Width Modulation (PWM) of current waveforms also demonstrate that for a wide range of wave speed excitations, PWM scheme should be combined with other control strategies for uniform current level regulations.

This study presents a new single-phase topology for the power injection system of a grid-connected photovoltaic generation system that is based on the parallel association of two voltage-source inverters: one is a three-level inverter with clamping diodes (or neutral point clamped) with a low switching frequency strategy (equal to the grid frequency) and the other is a two-level inverter which operates with a current hysteresis band strategy and an usual switching frequency (5–20 kHz). The main advantage of the proposed topology is to optimise the system design, allowing high power injection with a significant reduction of system losses (mainly switching losses) and achieving an increase of the energy injected into the grid. The performance of the proposed topology and its control algorithms are tested and validated using a laboratory prototype.

This study presents a backstepping power control (BPC) design for the grid-side voltage source converter (GSVSC) in a voltage source converter-based high-voltage dc (VSC-HVDC) wind power generation system. First, a dynamic model by taking parameter variations and external disturbances into account is derived on the basis of the space-vector theory to achieve the decoupling control characteristic of the GSVSC in the VSC-HVDC. Moreover, based on the backstepping design procedure, a BPC scheme is developed in the sense of Lyapunov stability theorem for the GSVSC to satisfy multiple objectives of a stable HVDC bus and the grid connection with a unity power factor. The salient feature of the proposed BPC is the introduction of additional error terms into the control laws to reduce the chattering phenomena in traditional backstepping control. In addition, the effectiveness of the proposed BPC scheme is demonstrated by numerical simulations on a doubly-fed induction generator wind farm with VSC-HVDC grid connection, and its advantage is indicated in comparison with a traditional proportional-integral control strategy under a wide range of operating conditions and the possible occurrence of uncertainties.

The present study has as main goal to make a technical and financial feasibility study of a photovoltaic powered reverse osmosis (PV–RO) and pumping system developed at the Renewable Energies Laboratory, Federal University of Ceará, in Fortaleza, Brazil, with the aim to supply drinking water for human consumption at low cost from brackish water in semi-arid areas. The research intends to determine parameters like drinking water production, specific energy consumption and specific costs, as well as the optimal system size regarding financial viability. The used configurations allow comparing two strategies: with and without batteries. The research was conducted with different levels of brackish water salinity, to identify a viability limit. The technical and financial analysis show that the unit produces satisfactory and competitive results, comparing with different plants in the world, concluding that, assuming a 2748 mg/l brackish water well, the configuration that brings the best cost/benefit is the no battery plant using 3 PV panels, which provides a daily production of 175 l of drinking water at 324.60 mg/l, with a specific consumption of 3.12 kWh/m³ and presenting a competitive specific cost of 10.32 US$/m³.

Distributed generation systems (DGS) with fixed-speed induction-generator-based wind turbines (FSWT) are sensitive and vulnerable to voltage disturbances and reactive power deficiency. Consequently, the control and protection strategies for such a DGS should be prompt and precise to avoid undesired wind generator cutting off. This study investigates and analyses the dynamic characteristics of an FSWT to reveal the behaviours of an FSWT under disturbances. Then a fast control strategy for stabilising an islanded DGS is proposed. The main contributions of the control strategy are: the total amount of reactive power compensation and load shedding may be determined precisely; all the operation execution points may be decided accurately to improve DGS stability. Furthermore, the implementation of the fast control strategy is also discussed. A case study is presented to demonstrate the effectiveness of the proposed method.

As wind turbines increase in power output, their size and mass grows as well. The development of offshore wind farms demands higher reliability to minimise the maintenance cost. Direct drive electrical generators offer a reliable alternative to conventional doubly fed induction generator machines since they omit the gearbox from the drive train. A fundamental issue for these generators is their large size which makes them difficult to manufacture, transfer and assemble. This study will investigate an analytical and a finite element analysis optimisation technique developed for minimising the structural mass of a direct drive generator. Both tools seek to minimise the mass of three different permanent magnet direct drive (PMDD) generators with 5 MW nominal power output while keeping a set of deflection criteria under limitations. The results indicate that the structural mass of a 5 MW PMDD generator can be effectively reduced with the help of these design tools. The research concludes in favour of a specific transversal flux PMDD topology, of which the electromagnetic topology benefits the structural design.

This study presents two methods for designing power oscillation damping (POD) controllers for wind farms comprising doubly fed induction generators (DFIGs). The first is the residue method, which uses linear feedback. The second method uses a non-linear signal as feedback. Here linear matrix inequalities (LMIs) and regional pole placement are used to determine the feedback gains for multiple wind farms simultaneously so that the power system satisfies a minimum damping ratio. The impact of the designed POD controllers in wind farms is demonstrated in a test power system. Modal analysis is used to design controllers using both the residue and LMI methods, and dynamic simulations are used to demonstrate the contribution of the wind farms to power system damping. Numerical simulations show that DFIGs, such as those found in wind farms, are capable of damping oscillations, and also illustrate the effectiveness of using non-linear feedback controllers.

Wind turbine (WT) technology is currently driven by offshore development, which requires more reliable, multi-megawatt turbines. Models with different levels of detail have been continuously explored but tend to focus either on the electrical system or the mechanical system. This study presents a 4.5 MW doubly-fed induction generator (DFIG) WT model with pitch control. The model is developed in a simulation package, which has two control levels, the WT control and the DFIG control. Both a detailed and a simplified converter model are presented. Mathematical system block diagrams of the closed-loop control systems are derived and verified against the simulation model. This includes a detailed model of the DC-link voltage control – a component which is usually only presented in abstract form. Simulation results show that the output responses from the two models have good agreement. The grid-side converter control with several disturbance inputs has been evaluated for three cases and its dynamic stiffness affected by operating points are presented. In addition, the relation of pitch controller bandwidth and torsional oscillation mode has been investigated using a two-mass shaft model. This model can be employed to evaluate the control scheme, mechanical and electrical dynamics and the fault ride-through capability for the turbine.