The use of distributed energy resources (DER) is increasingly being pursued as a supplement and an alternative to large conventional central power stations. The specification of a power electronics interface is subject to requirements related not only to the renewable energy source itself but also to its effects on power system operation, especially where the intermittent energy source constitutes a significant part of the total system capacity. In this paper, new trends in power electronics for the integration of wind and photovoltaic power generators are presented. A review of appropriate storage systems technology used for the integration of intermittent renewable energy sources is also introduced. Discussions about common and future trends in renewable energy systems based on reliability and maturity of each technology are presented.

A substantial increase of photovoltaic (PV) power generators installations has taken place in recent years, due to the increasing efficiency of solar cells as well as the improvements of manufacturing technology of solar panels. These generators are both grid-connected and stand-alone applications. We present an overview of the essential research results. The paper concentrates on the operation and modeling of stand-alone power systems with PV power generators. Systems with PV array-inverter assemblies, operating in the slave-and-master modes, are discussed, and the simulation results obtained using a renewable energy power system modular simulator are presented. These results demonstrate that simulation is an essential step in the system development process and that PV power generators constitute a valuable energy source. They have the ability to balance the energy and supply good power quality. It is demonstrated that when PV arrayinverters are operating in the master mode in stand-alone applications, they well perform the task of controlling the voltage and frequency of the power system. The mechanism of switching the master function between the diesel generator and the PV array-inverter assembly in a stand-alone power system is also proposed and analyzed. Finally, some experimental results on a practical system are compared to the simulation results and confirm the usefulness of the proposed approach to the development of renewable energy systems with PV power generators.Index Terms-Autonomous power systems, master/slave inverter operation, photovoltaic (PV) systems, power system modeling and simulation.

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Large loading events on wind turbine rotor blades are often associated with transient bursts of coherent turbulent energy in the turbine inflow. These coherent turbulent structures are identified as peaks in the three-dimensional, instantaneous, turbulent shearing stress field. Such organized inflow structures and the accompanying rotor aeroelastic responses typically have timescales of only a few seconds and therefore do not lend themselves to analysis by conventional Fourier spectral techniques. Wavelet analysis offers the ability to study more closely the spectral decomposition of short-period events such as the interaction of coherent turbulence with a moving rotor blade. In this paper we discuss our initial progress in the application of wavelet analysis techniques to the decomposition and interpretation of turbulence/rotor interaction. We discuss the results of using both continuous and discrete wavelet transforms for our application. Several examples are given of the techniques applied to both observed turbulence and turbine responses and those generated using numerical simulations. We found that the presence of coherent turbulent structures, as revealed by the inflow Reynolds stress field, is a major contributor to large load excursions. These bursts of coherent turbulent energy induce a broadband aeroelastic response in the turbine rotor as it passes through them.the maximum elevation of the rotor. The vertical stability is expressed by the gradient Richardson number defined aswhere g is the gravitational acceleration, z is the height (m), Â m the layer mean thermodynamic potential temperature (K) given byand T z and p z are the temperature (K) and barometric pressure (hPa) at height z.The covariance u 0 w 0 represents one off-diagonal component of the mean Reynolds stress tensor in turbulent flow. The remaining off-diagonal components include u 0 v 0 and v 0 w 0 , where v 0 is the zero-mean, lateral wind component. In a well-mixed, homogeneous boundary layer over flat terrain, only u 0 w 0 is generally non-zero. However, when turbulence contains motions that are both spatially and temporally organized, i.e. there is a definite phase structure between the velocity components, all three of the off-diagonal Reynolds stress components can be finite. Instantaneously, all three components can take on large positive or negative values. The passage of an organized patch of turbulence can be identified using an anemometer capable of rapid, simultaneous measurement of multi-axis wind components. Coherent turbulent structures can contain large velocity shears over small distances as well as significant local vorticity. Moderate-to high-speed flows that are just slightly or weakly stable (Ri small but positive) often contain small, energetic turbulence structures that, when ingested by wind turbine rotors, increase fatigue damage. 2 In the discussion following, references to the turbulent Reynolds stresses include only the off-diagonal terms u 0 w 0 , u 0 v 0 and v 0 w 0 .The examination of many load histories with...

We investigated a small isolated hybrid power system that used two types of power generation; wind turbine and diesel generation. The interaction of diesel generation, the wind turbine, and the local load is complicated because both the load and the wind turbine fluctuate during the day. These fluctuations create imbalances in power distribution (energy sources are not equal to energy sinks) that can affect the frequency and the voltage in the power system. The addition of energy storage will help balance the distribution of power in the power network.For this paper, we studied the interaction among hybrid power system components and the relative size of the components. We also show how the contribution of wind energy affects the entire power system and distribution and the role of energy storage under the transient conditions caused by load changes and wind turbine start ups. Index Terms -wind turbine, diesel generator, hybrid power system, renewable energy, energy storage.Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to