G. Vazquez

Transformerless single-phase multilevel inverter for grid tied photovoltaic systems

Single-phase transformerless photovoltaic (PV) inverters have become more widespread in the solar energy market. This is due to the higher efficiencies they achieve together with the very low ground currents, which are their main advantages. In this paper a multilevel transformerless single-phase topology, based on the H-bridge with an active clamping, is proposed. Multilevel output voltage is achieved by using a split DC link and an active bidirectional switch to clamp the first leg in the H-bridge circuit. Therefore, a good behavior is achieved regarding total harmonic distortion (THD). A sinusoidal based pulse width modulation (PWM) strategy is also proposed to control the power converter. Numerical results show that the proposed PV inverter complies with the transformerless norms and regulations, operating with high efficiency, and being suitable for the transformerless PV inverters market.

Comparative evaluation of L and LCL filters in transformerless grid tied converters for active power injection

This paper presents a comparison between two different passive filters for power converters tied to the grid with the application of active power injection. It addresses the L (inductive) filter and the LCL (inductive-capacitive-inductive) filter in single-phase power converters for which are presented the parameter design and modeling. These filters provide coupling of the power converter to the electrical grid and mitigation of high frequency harmonics which are inherent to switching power converters. It is obtained the state-space model and the transfer function of both type of filters and some design considerations for active power injection are presented. An evaluation, by means of numerical simulations, is presented for a single-phase H-bridge inverter with unipolar pulse width modulation for active power injection.

A current mode control for a single phase full bridge Power Factor Compensator

In this paper is presented a model based current controller for a Single Phase Power Factor Compensator (PFC). The proposed controller is based a description of the average model of the system. This control scheme is designed in two loops, namely the inner control loop or current loop and the outer loop or voltage loop. The first loop is aimed at compensating reactive power and current harmonic distortion in a single phase system, i.e. at guaranteeing a power factor close to unity. An adaptation scheme is introduced to cope with harmonic uncertainties in the system signals and system parameters. Additionally, an estimate of the series resistance is proposed to cope with the series resistor of the filter. The adaptation schemes proposed in the control law are reduced to a bank of resonant filters. These filters are tuned at the frequencies of the harmonics under compensation, which provides precise selective harmonic compensation. The second loop is designed to regulate the voltage load and it consists of a well known Integral plus Proportional controller (PI). Given that the output of the PI controller is a modulating signal which is used to construct the current reference, it has to include a Low Pass Filter (LPF) to restrict the bandwidth of the controller and avoid the harmonic pollution in a current reference which is produced by the rectification process. The topology selected for the PFC consists of a single phase full-bridge Voltage Source Inverter (VSI). The proposed control scheme and the power converter has been simulated and the results are presented here.

Model-based controller for current injection with a single phase NPC inverter

This paper presents the modeling and controller design for a neutral point clamped multilevel converter (NPC) which is used to inject power into the grid. The current injection to the grid is motivated by two main goals. One of them consists in using the inverter to provide power to the network; in this case the energy is taken from an external source and is supplied to the mains. On the other hand, the inverter can also be used for the harmonic compensation of currents caused by nonlinear loads. The proposed controller is designed to inject a sinusoidal current into the grid using an external DC voltage source. And also the converter in the presence of a nonlinear load in a common connection point behaves as an active power filter to compensate harmonic distortion in the current. The selected topology is connected to the mains through an L filter. In order to assess the performance of the proposed controller, simulation results are presented for an NPC converter connected on a common connection point with a nonlinear load.

A model-based controller for a half-bridge NPC used as an active power filter

This paper presents a model-based controller for an active power filter (APF) to compensate reactive power and current harmonic distortion in a single-phase system. A Half-bridge Neutral Point Clamped (NPC) topology is selected as a voltage source inverter (VSI) to implement the APF. The control scheme is composed by three control loops referred as the inner control loop (or current loop), the regulation loop, and the balance control loop. The inner control loop is aimed to compensate both the displacement power factor (DPF) and the harmonic distortion of the current flowing to the grid. Only compensation of odd harmonics is considered which is the distortion present in most single-phase non-linear loads. The regulation and balance loops are designed to achieve the regulation and balance of the capacitor voltages in the DC-link. Numerical results are presented to show the performance of the proposed solution.

Reduced output current ripple DC-DC buck converter control

In this paper the analysis and control of a buck converter with an LCLC filter at the output is addressed. The proposed LCLC output filter buck converter and controller achieve highly reduced output current ripple and reduced passive component values by replacing the common LC output filter by an LCLC network. The converter has an increased power density at reduced costs and reduced power losses. The controller provides the necessary damping to prevent undesired oscillating behaviors and to assure closed-loop asymptotic stability. The solution, that is the LCLC output filter buck converter plus control, is aimed at supplying to sensitive power loads such as electrolytic capacitors, supercapacitors, batteries and fuel cells in later stages of power electronics systems. Numerical results are presented to show the performance of the proposed solution.

A comparative analysis of the 5L-AH6 and 5L-SC topologies for grid-connected transformer-less multilevel inverters for PV systems

In this paper a comparative evaluation of the efficiency for two multilevel topologies used in grid-connected transformer-less applications is presented. The proposed analysis is focused in two of the most important characteristics in grid-connected converters, such as the leakage currents which appear between the stray capacitances and the ground path and the efficiency. The efficiency evaluation includes an analysis of power losses distribution in the semiconductors providing information to develop a good thermal design of the converter. For the evaluation is considered that the overall DC link is fixed to the desired voltage value and the capacitor voltages are balanced. Also, the topologies selected are connected to the grid by means of an ideal L filter to inject active power to the grid. In both cases, the proposed modulation strategy is based in the Sinusoidal Level Shifted Pulse Width Modulation (SLSPWM). Numerical results of the analysis of common mode voltage and the efficiency curves are presented.

A model-based controller of a three-level stacked-cell grid connected converter

This paper presents a model-based controller for a single-phase grid-tied transformerless multilevel PV inverter. The selected topology is known as single-phase three-level stacked-cell (3L-SC). It is based on the conventional H-bridge, where a multilevel output voltage is achieved by using a split DC-link with an active bidirectional switch. The proposed controller comprises a current control loop aimed to guarantee active power injection, and a voltage balance loop aimed to balance the capacitor voltages in the split DC-link. In the inner loop, a sinusoidal current in phase with the grid voltage is injected in spite of harmonic distortion present on the voltage signal. For this, the inner loop includes a particular modification of a repetitive scheme, which is able to handle a fractional delay issue. A pulse width based modulation strategy is also proposed to generate proper switching sequences for the switching devices in the multilevel inverter. Numerical results are presented to show the performance of the proposed solution.

An improved current mode control of a three-phase rectifier based on positive-sequence detection

In this paper an improved current mode control for a three-phase rectifier is presented which is able to compensate the line currents under unbalanced operation of the supplied grid voltage. Instrumental for the controller design is the computation of the current reference, where, the key point is the use of the positive-sequence of the grid voltage to construct it. The control scheme is designed to guarantee current tracking of the positive-sequence of the grid voltage and the average voltage regulation at the output towards the desired voltage reference. The overall resulting controller is composed by two main control loops, namely, current (or inner), the voltage (or outer) control loops and additionally a positive-sequence estimator of the grid is used to compute the current reference. The current control loop is designed as a proportional controller with a couple of adaptive estimators which have been added to cope with parameter uncertainties of the filter. The voltage control loop consists of an Integral plus a Proportional controller whose output signal acts as a modulating signal of the current reference.

Proyecto TAGFACT: Del texto al conocimiento. Factualidad y grados de certeza en español

El objetivo general de este proyecto es crear una herramienta para la anotacion de la factualidad expresada en textos en espanol a traves del procesamiento automatico. Pretendemos que dicha representacion sea muy rica, por lo que se llevara a cabo desde tres ejes distintos: multinivel, multidimensional y multitextual. El analisis multinivel da cuenta de las distintas marcas linguisticas que expresan el grado de certeza de un evento a nivel morfologico y sintactico, pero tambien discursivo; el analisis multidimensional, de un numero variado de las voces que evaluan dicho evento; y el analisis multitextual, de distintos textos sobre un mismo evento, siendo este ultimo uno de los aspectos mas innovadores de la propuesta.