M. A. Juarez

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.

A model-based controller for a DC-DC boost converter with an LCL input filter

This paper studies a modified DC-DC boost converter where the input inductance has been replaced by an LCL filter. The voltage conversion ratio of the proposed converter is equivalent to the conversion ratio of a conventional boost converter, and it has only one active switching device. A controller is proposed to regulate the output voltage to a given reference with guaranteed reduced input current ripple, i.e., high-frequency current components are minimized at the input current source. Low current ripple is required when dealing with sensitive electric power sources such as fuel cells, batteries and electrolytic capacitors used at DC-links in power electronics applications. The controller design follows a Lyapunov approach, and provides active damping to the input LCL filter. Numerical simulations are presented to evaluate the closed-loop performance.

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.

Analysis of buck converter control for automobile LED headlights application

This paper presents an electronic ballast based high power LEDs for headlights automobile. The ballast is based on a buck converter to feed a load of high power LED. The load is divided into five high power LED (10W), in automobile lighting systems rapid changes of lighting is required (power changes), therefore the buck converter must deliver constant voltage levels to changes in power and further the current necessary to maintain a flow of light required. To solve this problem this paper proposes a control law for buck converter control, which maintains a fixed voltage level for the different power (10.9W, 21.8W, 32.7W, 43.6W, 54.5W) dynamic response to these changes is fast and constant levels of current and luminous flux at each change of load is maintained.

Design of self-oscillating electronic ballast for power LEDs

This paper presents a self-oscillating electronic ballast for a 36 W LED string. The design consists of a simple control that reduces the component number and cost of the ballast. Self-oscillating converters are popular in compact fluorescent lamps; therefore, it is proposed the use of this self-oscillating control technique for the LED lamp. The self-oscillating LED driver represents a very suitable solution in compact LED products. This paper describes the design of a self-oscillating electronic ballast at high frequency. The output of the sine wave of the resonant inverter is rectified and, then its high frequency yields a reduction in the value of output capacitor.

A model for electrical characteristics of high power UV LED

In this paper presents the study and implementation of a model for an ultraviolet light-emitting diode (UV LED). This model is used to characterize series and parallel UV LED arrangements. The proposed model can be used for different power LED. An exponential expression of a term that describes the electrical characteristics of the V-I curve of a UV LED is used. The principle of implementation of UV LED is described, and in this way they can be used in simulation software. The proposed model this designed for any number of LED in series or parallel. To perform the proposed model radiation is analyzed in terms of temperature and power.

Comparative analysis of the reliability of drivers for power LED

This paper presented a comparative study in function reliability between dc-dc converters used in power LED. Between dc-dc converters more used to power LED are the Buck and Flyback converter, because the Buck provides a lower output voltage than the input, and in the case of flyback has galvanic isolation. The study has objetive to determine the reliability obtaining the failure rate of the system and the average time when failures occurs, because the LED driver must have an average life similar to the LED lamp. The reliability analysis is based in the standard MIL-HDBK-217, for this study performed was used a LED load of 54.6 W in both converters. The results have shown that the buck converter has a lower failure rate and a higher mean time between failures, therefore has a longer useful life.

Comparative evaluation of load observers for a quadratic boost converter

Cascaded DC-DC boost power converters are topologies that have as main advantage their high voltage step-up ratio. This feature makes them suitable in applications, for instance, in non-conventional electric energy systems such as in photovoltaic, wind-turbine, battery and fuel cell applications, among others. However, the control of these power converters, commonly requires the computation of the voltage and current references. For some controllers, which are already reported in the literature, the knowledge of the value of the load is essential for operation in load-changing conditions. In this paper is addressed a comparative evaluation of three different load observers for the two stage, or quadratic, boost converter. Numerical simulations of each estimator and discussion about its performance are presented.

Analysis and design of resonant inverter for ozone generation

This article analyzes a resonant inverter to feed an ozone cell. The resonant inverter consists of a full bridge and a resonant tank to generate a high frequency sine wave. The article proposes the study of three resonant tanks in order to determine which has the greatest gain in current and voltage. The resonant tanks to be analyzed are the resonant tank RSE series, parallel resonant tank transformer PRT and the series resonant tank transformer SERT. It was determined that the tank SERT has better characteristics for use in cells ozone, the design have shown that the load has little effect on the resonance frequency allowing various types of cells ozone.

Comparative study of two model-based controllers for a quadratic boost converter

Two model-based controllers for the quadratic boost converter with different number of sensors are presented and compared. The quadratic boost converter model is a bilinear control system whose linearization has complex right-half plane zeros. Common-use controllers consist in current and voltage control loops and rely on the requirement that the current dynamics is faster than the voltage dynamics. Controllers that are reviewed in this paper aim at the output voltage regulation and are obtained by requiring that the derivative of an energylike function be negative semi-definite along the trajectories of the closed-loop system. The considered controllers make use the complete four state variables and a subset of the state variables. The controllers include a load conductance estimation scheme to cope with possibly variations of the converter load. Closed-loop operation is verified via numerical simulation under equal conditions.