Low Voltage Ride-Through of Single-Phase Transformerless Photovoltaic Inverters Yongheng Yang Frede Blaabjerg Huai Wang Aalborg University, Aalborg Denmark

Y. Yang, F. Blaabjerg, and H. Wang "Low voltage ride-through of single-phase transformerless photovoltaic inverters,” IEEE Trans. Industry Applications, in press.

 Abstract 
Transformerless photovoltaic (PV) inverters are going to be more widely adopted in order to achieve high efficiency, as the penetration level of PV systems is continuously booming. However, problems may arise in highly PV-integrated distribution systems. For example, a sudden stoppage of all PV systems due to anti-islanding protection may contribute to grid disturbances. Thus, standards featuring with ancillary services for the next generation PV systems are under a revision in some countries. The future PV systems have to provide a full range of services as what the conventional power plants do, e.g. Low Voltage Ride-Through (LVRT) under grid faults and grid support service. In order to map future challenges, the LVRT capability of three mainstream single-phase transformerless PV inverters under grid faults are explored in this paper. Control strategies with reactive power injection are also discussed. The selected inverters are the full-bridge inverter with bipolar modulation, the full-bridge inverter with DC bypass and the Highly Efficient and Reliable Inverter Concept (HERIC). A 1 kW single-phase gridconnected PV system is analyzed to verify the discussions. The tests confirmed that, although the HERIC inverter is the best candidate in terms of efficiency, it is not very special feasible in case of a voltage sag. The other two topologies are capable of providing reactive current during LVRT. A benchmarking of those inverters is also provided in this paper, which offers the possibility to select appropriate devices and to further optimize the transformerless system.

ORIGINAL URL

http://vbn.aau.dk/files/102349282/77954_tia.2013.2282966.pdf

A Simple procedure to evaluate the efficiency and power density of power conversion topologies for offshore wind turbines Rene Barrera-Cardenas,∗ , Marta Molinas Department of Electric Power Engineering, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway

Abstract
The prospective development of the offshore wind energy conversion system is mainly promoted by demand for higher efficiency and power density. This paper describes a simple procedure to calculate the efficiency and power density of power conversion systems for offshore wind turbines. The proposed method can be used as starting point into the linear design process to calculate the losses in semiconductors and transformer as well as the volume of main elements. With the losses and volumes, efficiency and power density can be calculated. In order to illustrate the evaluation procedure, the reduced matrix converter with single-phase transformer is considered like example topology. The Efficiency-Power-density Pareto Front is obtained for a set of design parameters. The methodology is eminently suitable for comparison of power converter with different topologies. © 2012 Published by Elsevier Ltd.
LINK FULL PAPER
http://www.sciencedirect.com/science/article/pii/S1876610212011423