Gerardo Vazquez

A New High-Efficiency Single-Phase Transformerless PV Inverter Topology

There is a strong trend in the photovoltaic inverter technology to use transformerless topologies in order to acquire higher efficiencies combining with very low ground leakage current. In this paper, a new topology, based on the H-bridge with a new ac bypass circuit consisting of a diode rectifier and a switch with clamping to the dc midpoint, is proposed. The topology is simulated and experimentally validated, and a comparison with other existing topologies is performed. High conversion efficiency and low leakage current are demonstrated.

Modeling of a variable speed wind turbine with a Permanent Magnet Synchronous Generator

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.

Photovoltaic inverters with fault ride-through Capability

This paper presents a new control strategy that allow the photovoltaic system operate under grid faults without overpass the rated current and assuring sinusoidal currents. In the classic control strategies used in photovoltaic systems the power delivered to the grid remains constant when a fault occurs, hence the current can reach dangerous values. Therefore the converter has a protection system to disconnect it avoiding its damage. Thus it must be connected manually when the electrical grid is re-established. The strategy presented here overcomes these drawbacks. It is compared with the classic strategy through simulations in PSCAD and the experimental results prove its effectiveness.

Losses and CMV evaluation in transformerless grid-connected PV topologies

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.

Adaptive hysteresis band current control for transformerless single-phase PV inverters

Current control based on hysteresis algorithms are widely used in different applications, such as motion control, active filtering or active/reactive power delivery control in distributed generation systems. The hysteresis current control provides to the system a fast and robust dynamic response, and requires a simple implementation in standard digital signal platforms. On the other hand, the main drawback of classical hysteresis current control lies in the fact that the switching frequency is variable, as the hysteresis band is fixed. In this paper a variable band hysteresis control algorithm will be presented. As it will be shown, this variable band permits overcoming the aforementioned problem giving rise to an almost constant switching frequency. The performance of this algorithm, together with classical hysteresis controls and proportional resonant (PR) controllers, has been evaluated in three different single-phase PV inverter topologies, by means of simulations performed with PSIM. In addition, the behavior of the thermal losses when using each control structure in such converters has been studied as well.

Grid synchronization for advanced power processing and FACTS in wind power systems

The high penetration of wind power systems in the electrical network has introduced new issues in the stability and transient operation of the grid. By means of providing advanced functionalities to the existing power converters of such power plants it is possible to enhance their performance and also to support the grid operation, as the new grid codes demand. The connection of FACTS based on power converters, such as STATCOMs, are also contributing to the integration of renewable energies improving their behavior under contingencies. However, in both cases it is needed to have a grid voltage synchronization system, able to work under unbalanced and distorted conditions. This paper presents the discrete representation and performance of three PLLs structures, designed to work in that kind of situations. Their synchronization capability will be tested in different scenarios and their performance constraints will be established according to the Grid Code Requirements (GCRs)

A photovoltaic three-phase topology to reduce Common Mode Voltage

At the present time most of the photovoltaic (PV) applications require to be integrated to the electrical grid. There are mainly two types of PV systems: with galvanic isolation (transformer) and transformerless. PV systems with low frequency transformer provide galvanic isolation from the grid. However, this transformer increases the losses, size and cost. On the other side, when the transformer is not included, the system can generate strong ground currents which are a function of the stray elements (capacitances). In this sense reducing the Common Mode Voltage (CMV), is an important issue in the design of power electronics converters for transformerless PV applications. In this paper a three-phase transformerless PV inverter with reduce common mode voltage is introduced. CMV is analyzed under different modulation schemes and an analysis of losses using a real model of the IGBTs is included

Intelligent control agent for transient to an island grid

The increasing penetration of generation power plants based on renewable energies in the electrical networks has boosted the number of systems connected to the grid. In this scenario the microgrid, providing advanced functionalities to improve the stability and operation of the network, have become very popular. In this paper a control strategy for the microgrid management is presented. The proposed system improves the performance of microgrids and its interaction with the main network, or another microgrid, under grid voltage transients. This technique gives rise to a simple and robust control scheme to ensure the appropriate microgrid disconnection from the main grid. In the following the control algorithm for the intelligent connection agent will be shown, and the grid synchronization system, as well as the voltage and current control loops will be detailed. Finally simulation results obtained using the MATLAB/Simulink & Psim platform will be presented and discussed

Photovoltaic plants generation improvement using Li-ion batteries as energy buffer

this paper analyzes the PV power plants operability improvement obtained when introducing energy storage (ES) systems which allow decoupling the power received from the sun on the photovoltaic (PV) panels from the power injected by the power plant into the grid. Two energy management strategies are presented and analyzed, using Li-ion batteries as the energy storage buffer. The generated power redistribution and its variability reduction are All the results obtained in this paper are based on one year long simulations which used real irradiance data sampled every two minutes.

Model based controller for an LCL coupling filter for transformerless grid connected inverters in PV applications

Voltage source inverters (VSI) connected to the grid by means of LCL filters offer benefits in the injection of active power into the grid, since they provide low harmonic distortion and a small size of the output filter. However LCL grid connected VSI must be designed in order to provide damping at the filter resonance frequency. This paper presents the design and analysis of a model based controller for an LCL coupling filter to inject active power into the grid for single phase photovoltaic transformerless applications. The control objectives are to provide closed-loop stability and to assure that the current to be injected follows a reference which is proportional to the grid voltage. Therefore, these objectives guarantee the active power injection to the grid. The proposed output feedback controller is based on the error model of the LCL filter and makes use only of the measurements of the output current of the inverter and the grid voltage.