This paper presents a single-phase transformerless grid-connected photovoltaic converter based on two cascaded full bridges with different dc-link voltages. The converter can synthesize up to nine voltage levels with a single dc bus, since one of the full bridges is supplied by a flying capacitor. The multilevel output reduces harmonic distortion and electromagnetic interference. A suitable switching strategy is employed to regulate the flying-capacitor voltage, improve the efficiency (most devices switch at the grid frequency), and minimize the common-mode leakage current with the help of a novel dedicated circuit (transient circuit). Simulations and experiments confirm the feasibility and good performance of the proposed converter

Photovoltaic (PV) power systems have been in the spotlight of scientific research for years. However, this technology is still undergoing developments, and several new architectures are proposed each year. This study describes the main challenges facing grid-connected PV systems without galvanic isolation, then carries out a review of the state-of-the-art of single-phase systems. The converter topology review is focused on the match between the different types of converters and the different PV panel technologies, determined by the common-mode voltage between the PV string terminals and the ground. The ground leakage current, due to time variations of this voltage, is a source of electric safety and electromagnetic interference (EMI)-related problems, and its amplitude is constrained by international standards. The basic principles of operation of the different solutions are described, along with their strengths and drawbacks. Conversion efficiency is evaluated qualitatively comparing the semiconductor power losses. Finally, the future trends regarding semiconductor devices, PV panels and international regulations for single-phase grid-connected equipment are discussed, and indications on how these might steer future research efforts in PV converters are inferred

Abstract-The More Electric Aircraft concepts aims at increasing the penetration of electric systems on the aircrafts. In this framework, the electrical power distribution system (EPDS) is of high importance. In order to improve the utilization of the generators and face the peak power demand without disconnecting the loads, different technologies of storage are employed. This paper proposes the use of a Quadruple Active Bridge converter, already employed in other fields, to interface a fuel cell, a battery and a supercapacitor bank to the DC bus of the EPDS. This objective can be achieved by employing multiple DC/DC converters, that allow an individual control of the energy sources and a good efficiency. Obtaining the same power control and efficiency with a multi-port power converter constitutes a challenge which is worth taking to reduce cost, volume and weight and increase the system reliability. A novel control based on PI controllers in conjunction with a decoupling system and current feed-forward allow shaping the power request to each port. This, however, leads to an asymmetrical loading of each port, which could decrease the efficiency. A laboratory prototype is used to confirm that this asymmetrical kind of operation, where each port processes a different amount of power, does not imply a marked reduction of efficiency.

This paper presents a modified two-level three-phase inverter for the reduction of the leakage current. With respect to a traditional two-level inverter, the proposed solution reduces the common-mode voltage, both in amplitude and frequency. Between the DC source and the traditional three-phase bridge, two active DC-decoupling devices and a voltage-clamping network have been added. A dedicated control strategy was developed adopting a modified Space Vector PWM modulation, oriented to the reduction of the common-mode voltage. Simulations showing the good performance of the solution are presented. A preliminary prototype was developed and experimental results are presented.

The design of a PV grid-connected converter usuallycomprehends a galvanic isolation between the grid and thephotovoltaic panels. Recently, in low power systems, thegalvanic isolation has been removed with the aim to increaseefficiency and reduce the cost of the converter. Due to thepresence of a parasitic capacitance between the photovoltaiccells and the metal frame of the PV panel, usually connected toearth, a high value of common mode current (i.e. groundleakage current) can arise. In order to limit the ground leakagecurrent (which deteriorates the power quality and generatesEMI), new converter topologies have been proposed. Theireffectiveness is based on the symmetrical (ideal) commutationsof the power switches and some of them adopt a further voltagelevel derived from a capacitive divider of the DC bus voltage.Unfortunately, in actual implementations, asymmetrical powerswitches transients and variations of this added voltage lead tohigher ground leakage current with respect to the ideal case.After a review of the state of the art this paper investigates thesetwo issues and presents a particular solution (based on digitalcontrol and PWM strategy) that, in conjunction with acompensation strategy of power switches actual commutations,guarantees low ground leakage current regardless theparameters tolerance of the power circuit. Simulation andexperimental results confirm the effectiveness of the proposedsolution