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It has been demonstrated that modulating the switching frequency of a power converter is a valuable way for reducing the electromagnetic interference (EMI) due to the switching process. Since we are considering a signal whose frequency content varies with time, wavelets are well suited to analyze the performance of such techniques. In this paper, we evaluate the performance of spread spectrum frequency modulation (SSFM) applied to the EMI reduction of a real power converter that uses periodic pattern switching frequency modulation. The performance of the converter under investigation includes the analysis of the switching voltage spectrum (as the main source of EMI) and the output voltage ripple. This evaluation is performed with two coefficients, i.e., maximum energy ratio (MER) and energy dispersion ratio (EDR), which are figures of merit defined in this paper using time-dependent energy density distribution in frequency, obtained from the scalograms of the analyzed signals. Such figures of merit allow comparison in the time-frequency domain of different modulation techniques and the choice of the best solution for each case in terms of reduction of the peak of noise spectrum. Index Terms--DC-DC power conversion, electromagnetic compatibility, pulsewidth modulation, switching circuits, time-frequency representation, wavelet transform.

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 array-inverters 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.

Renewable-energy systems that are under development need a simulation-based analysis to ensure system stability, power quality, and reliability. Such an analysis may reveal design modifications that need to be made before the system is implemented in the field. The modular simulator RPM-Sim, available on the National Renewable Energy Laboratory Web site (http://wind.nrel.gov/designcodes/simulators/rpmsim/), facilitates a low-cost application-specific study of the dynamics of the wind-solar-diesel hybrid power systems. This paper discusses the principal modules of the simulator and provides several examples of a simulation-based analysis of the renewable-energy systems. These examples illustrate the importance of a simulation-based study of the grid-connected and stand-alone or autonomous systems. The RPM-Sim is open-ended and can be easily expanded. Index Terms--Modeling and simulation of power systems, peak-power tracker (PPT), renewable-energy systems, stiff grid, water pumping, weak grid, wind-farm aggregation.

The use of distributed energy resources is increasingly being pursued as a supplement and an alternative to large conventional central power stations. The specification of a power-electronic interface is subject to requirements related not only to the renewable energy source itself but also to its effects on the 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 (PV) power generators are presented. A review of the appropriate storage-system 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. Index Terms--Direct drives, doubly fed induction generator (DFIG), flywheel, hydrogen, multilevel converter topologies, supercapacitors, superconducting magnetic energy storage (SMES), wind diesel

Originally, adaptive control theory was developed for the ideal system models, i.e., linear system models under the assumption that relative degree and upper bounds on the order of the systems are known. At the beginning of the last decade, adaptive control algorithms designed for such ideal system models were strongly attacked by many researchers due to 'lack of robustness' in the presence of unmodeled dynamics and external disturbances. The purpose of the present paper is to relax existing constant pressure on the adaptive control algorithms originally designed for the ideal system models. It is shown that such adaptive control algorithms are globally stable and robust with respect to unmodeled dynamics and external disturbances without any modifications, such as i-Sigma-modification, Epsilon(sub 1)-modification, relative dead-zone, projection of the parameter estimates, etc. Global stability of the unmodified algorithms is established by requiring the reference signal to be persistently exciting.

The article discusses various reports published within the issue including one by M. Liserre on the an anti-islanding method for single-phase inverters based on a grid voltage sensorless control and another by D. M. Vilathgamuwa on the protection of microgrids during utility-voltage sags.

The article discusses various reports published within the issue of the periodical, including one by W. Xiao, M. G. J. Lind, W. G. Dunford, and A. Capel entitled "Real-Time Identification of Optimal Operating Points in Photovoltaic Power Systems."