In some photovoltaic (PV) applications, it is possible to remove the transformer of a system in order to reduce losses, cost, and size. In transformerless systems, the PV module parasitic capacitance can introduce leakage currents in which the amplitude depends on the converter topology, on the pulsewidth modulation, and on the resonant circuit comprised by the system components. Based on the common-mode voltage model, modulation techniques are proposed to eliminate the leakage current in transformerless PV systems without requiring any modification on the converter and any additional hardware. The main drawback is that the proposed modulation technique for two-level inverters can only be used with 650-V dc link in the case of a 110-V (rms) grid phase voltage. Comparisons among the modulation techniques are discussed, and it is proven that the proposed modulation for two- and three-level inverters presents the best results. To validate the models used in the simulations, an experimental three-phase inverter is used.

The aim of this work is to analyze a typical configuration of a wind turbine generator system (WTGS) equipped with a variable speed generator. Nowadays, doubly-fed induction generators are being widely used on WTGS, although synchronous generators are being extensively utilized too. There are different types of synchronous generators, but the multi-pole permanent magnet synchronous generator (PMSG) is chosen in order to obtain its model. It offers better performance due to higher efficiency and less maintenance since it does not have rotor current and can be used without a gearbox, which also implies a reduction of the weight of the nacelle and a reduction of costs. Apart from the generator, the analyzed WTGS consists of another three parts: wind speed, wind turbine and drive train. These elements have been modeled and the equations that explain their behavior have been introduced. What is more, the whole WTGS has been implemented in MATLAB/Simulink interface. Moreover, the concept of the maximum power point tracking (MPPT) has been presented in terms of the adjustment of the generator rotor speed according to instantaneous wind speed.

In this paper, a novel scheme for obtaining the fundamental-frequency positive-sequence grid voltage is proposed. The method is based on four simple mathematical transformations; two of them are in the stationary reference frame, which are able to eliminate odd harmonics from the original signals. The other two transformations are implemented in a synchronously rotating reference frame in order to eliminate even harmonics. The output of the last transformation block is the input to a synchronous reference-frame phase-locked loop for detecting the frequency and position of the positive-sequence voltage vector. The proposed algorithm was verified through simulations and experiments by applying distorted and unbalanced signals, containing positive and negative-sequence components. The results are in agreement with those theoretically predicted and indicate that the proposed scheme has a great potential for use in grid-connected converter synchronization algorithms.

Most of the photovoltaic (PV) models involve mainly the reproduction of the nonlinear I–V curves for PV modules with a certain degree of accuracy. Previous researches have used equivalent circuits based on common electronic devices to model the real behavior of PV modules, such as the single and double diode models. Unfortunately, those models are static, i.e., they can reproduce the I–V curve of a PV module for a specific environmental condition (fixed irradiance and temperature). As consequence, different models should be obtained for each different environmental condition, restricting the use of the models for a limited set of irradiance and temperature values. The first contribution of this paper is the proposition of an irradiance and temperature dependent double-diode model for PV modules. In this model, the internal parameters depend on the environmental conditions, extrapolating its use for temperature and irradiance values different from those the parameters were initially estimated. In addition, two parameter estimation techniques are proposed for this new model. The techniques use a combination of analytical equations and numerical optimization based on the pattern search algorithm. Comparison results based on experimental I–V curves of real PV modules are presented in order to prove the accuracy of the model and techniques.

This paper presents a study of two maximum power point tracking methods for grid connected photovoltaic systems. The best operation conditions of the perturbation and observation and the incremental conductance are investigated in order to identify the performances of photovoltaic systems. Improvements of these methods can be obtained with the best adjustment of the sampling rate and the perturbation size. Practical considerations about the incremental conductance are discussed and some modifications to overcome its problems are done. A procedure to determine the parameters is explained and it helps to define which method is better to the grid connected photovoltaic system with only one conversion stage. The methods influence the quality of the currents injected in the grid and this influence becomes the main parameter for choosing the incremental conductance. The improvement with the choice of the best parameters is proved by means of simulation and experimental results.

Controlling the thermal losses in the semiconductors as well as the Common Mode Voltage (CMV), are important issues in the design of power electronics converters for photovoltaic applications. At present time there are several topologies that offer a good performance regarding losses and CMV. In this paper an evaluation of three of these converters topologies: H5, HERIC and NPC transformerless for single phase PV systems will be carried out by means of simulations performed with PSIM 7.05. This software permits to estimate accurately the switching and conduction losses, thanks to its Thermal Module. This analysis together with the CMV study for each case will permit to establish the pros and cons of each topology.