Transformerless inverters are extensively employed in grid-connected photovoltaic (PV) generation systems due to its advantages of achieving low cost and high efficiency. However, the common-mode voltage issues have been motivated the proposition of new topologies, control, and modulation schemes. In common ground PV inverters, the grid neutral line is directly connected to the negative pole of the dc bus. Therefore, the parasitic capacitances are bypassed and the leakage current can be eliminated. In this paper, a five-level common ground transformerless inverter with reduced output harmonic content for PV systems is proposed. In addition, the proposed inverter can process reactive power and it presents a maximum dc-voltage utilization in opposition to half-bridge-based topologies. The operation modes of the proposed inverter, a simple modulation strategy, as well as the design guidelines are analyzed in detail. Finally, experimental results demonstrate the feasibility and good performance of the proposed inverter.

empty Transformerless inverters have attracted great attention since they became a compact and economic solution for photovoltaic (PV) generation systems. On the other hand, the common-mode (CM) leakage current issue needs to be addressed in order to meet safety requirements. This paper proposes a new multilevel common-ground inverter for transformerless systems. The leakage current is eliminated by the electric connection between the grid neutral point and the PV negative terminal. Furthermore, the operation modes of the proposed inverter, as well as the design guidelines are analyzed in detail. In addition, a feed-forward modulation strategy to decouple the output variables from the voltage capacitor oscillations is proposed. Experimental results are presented to verify the performance and practicability of the proposed inverter in grid-connected operation.

This study develops a generalised pulse width modulation (PWM) approach to eliminate both the low-frequency oscillations and imbalances in the dc-link capacitor voltages, which are the main drawbacks of diode clamped converters. The algorithm has been developed within the carrier-based PWM framework to facilitate its implementation in diode clamped converters with four or more levels. In addition, a generalised control strategy for dc voltage control is proposed and its stability is demonstrated. The good performance of the proposed modulation technique is demonstrated from simulation and experimental results for a four-level diode-clamped inverter.

H-bridge inverter is a common topology used for single-phase applications. Due to its limited voltage gain, a two-stage power conversion with a front-end dc–dc converter is usually adopted to accommodate the low dc source voltage. Recently, single-stage boost inverters are gaining significant interest due to their higher power efficiency and compactness. In this article, we present a family of boost inverters with continuous dc source current. By the incorporation of merely a power switch and a boost inductor to the first leg of H-bridge, voltage boosting and three-level generation can be simultaneously achieved within a single-stage operation. All potential topologies using the same number of components are derived. An extension to generate five voltage levels with voltage gain enhancement is also proposed. The operation of the proposed boost inverters is thoroughly analyzed. The simulation andexperimental results are presented for verification.

The split-source inverter (SSI) has been recently proposed as an alternative option to the commonly used Z-source inverter. This topology requires the same number of active switches of the conventional VSI, three additional diodes and the same eight switching states. This paper presents a finite set model predictive control (FS-MPC) for grid connected three-phase SSI's. The proposed controller perform a discrete-time model to predict the future behaviour of the input and output currents for each switching state, then a control action is defined by minimizing a proper cost function. Finally, simulation results are presented to demonstrate the good performance of the proposed controller.

This paper presents a new flexible arrangement of static converters for grid-connected wind energy conversion systems (WECS). The proposed arrangement uses three-phase voltage-fed back-to-back mass-produced power converter modules with reconfiguration switches. The main features of the proposed flexible arrangement are as follows: 1) expanded reactive power capability limits; 2) high efficiency, mainly under low wind conditions where the active power is reduced; and 3) low current harmonic content. In addition, a detailed description of the operating modes, as well as of the grid, generator, and circulating current controller design, are given. Finally, experimental results support the theoretical development, and demonstrate the good performance and flexibility of the proposed arrangement.