Transformerless inverters are being widely used in grid-connected photovoltaic (PV) generation systems. Transformer elimination, in grid-connected PV systems, has many advantages. This not only reduces cost, size, and weight, but also increases the whole system efficiency. However, once the transformer is removed, there is no galvanic isolation between grid and PV array; as a consequence, leakage current appears due to parasitic capacitance to the ground, resulting in prohibitive electromagnetic interference and security issues. This paper presents a novel topology in order to reduce this ground leakage current. It is established that the neutral line in the grid is the same as that of the negative terminal in a PV system, eliminating this way, any possibility of leakage current in this terminal. A sliding mode controller that controls the output current has been employed. The principle of operation of the transformerless inverter is analyzed, but also the topology has been simulated and experimentally tested.

In many emerging applications it is required a high boosting gain; in the literature has been proposed many topologies to make this possible, since the traditional dc-dc boost converter can not make the very high boosting function by itself. In this paper a different approach to obtain the high boosting gain is proposed: the tapped-inductor boost converter. This converter has few components and high efficiency, and also operates in a simple way. Analysis and experimental results are presented.

A single-phase common-mode transformerless grid-connected photovoltaic (PV) converter, which is based on the integration of two stages, is proposed in this paper. Transformer elimination in grid-connected PV systems has many advantages. It not only reduces cost, size, and weight but also increases the complete system efficiency. Since there is no galvanic isolation between grid and PV array, a leakage current may appear due to the PV parasitic capacitance to the ground, if this is not taken into account in the converter design. This paper presents a dc/dc boost converter integrated with a full-bridge inverter. The integration of these two stages reduces the ground leakage current. The neutral line of the grid is directly connected to the negative terminal of the PV array, eliminating any possibility of leakage current in this terminal. The principle of operation of the transformerless converter is analyzed, and a 200-W topology is experimentally tested.

The boost inverter is a device that is able to generate a sinusoidal voltage with an amplitude larger than the input voltage. Based on the idea of indirectly controlling the output voltage through the inductor current, a dynamical sliding-mode controller for the boost inverter is proposed in this paper. Unlike the usual approach of generating a sinusoidal voltage in both capacitors of the boost inverter, the strategy proposed in this paper focuses on generating a sinusoidal voltage on the load despite the voltage form of both capacitors. A consequence of doing so is that only the desired output voltage is required as reference to implement the controller. Furthermore, it has a fast response, is robust under load and input voltage variations, and yet, is remarkably simple to implement. Although it is strongly nonlinear, it can be implemented using standard electronics circuitry and only needs voltage measurements.

This paper shows a synchronization technique of power converters based on a limit cycle oscillator (LCO) and a frequency-locked loop (FLL), which makes the system frequency adaptive. The proposed technique LCO-FLL offers a high degree of immunity and robustness against swells, sags, harmonics, and phase-frequency shift. Furthermore, the LCO-FLL has the advantage of performing the synchrony with the grid from any initial condition set for LCO, ensuring an acceptable transient onto the synchronization process. Other advantages of the proposed scheme are that it does not require a phase-locked loop or trigonometric functions and it gives useful information to estimate the positive- and negative-sequence components in a three-phase system with a highly polluted grid scenario. In this paper, a local stability analysis of the LCO-FLL is presented. The behavior and performance of the proposed technique are compared with synchronization techniques by means of experimental results. Furthermore, a three-phase application of the synchronization technique is evaluated experimentally.

In this paper, the analysis and experimental study of three kinds of inverters are presented, beginning with the traditional full bridge buck inverter, followed by two different inverter approaches, the boost and buck boost ones. This last two converters have the property of produce an output voltage higher or lower than the input voltage additionally to its inversion capability, which is a desired characteristic to some applications. The paper includes a semiconductor device stress study of the different inverter approaches additionally to the analysis and experimental results of the converters. The control strategy used for all the converters is the sliding mode control in order to introduce a good dynamic response for the closed loop system.