Multiple single-active bridge (SAB) DC-DC converters are connected in the input-parallel and outputparallel (IPOP) configuration to achieve higher power output in many applications. Module shutdown, known as phase shedding, is used to improve light-load efficiency in the IPOP modular converter. The SAB is known for its simplicity and robustness, but it is only moderately efficient; therefore, larger snubber capacitance is used to lower switching and conduction losses in the SAB and improve efficiency. However, larger snubber capacitance increases minimum power and reduces load range in the SAB, resulting in the unattainability of certain load-range segments in the IPOP converter because capacitance increases when phase shedding is used. Hence, snubber capacitances across the modules are optimized to improve average efficiency while maintaining the existing load range. As a result, snubber capacitances differ across SAB modules. With nonidentical modules, nonuniform module power distribution is used in the IPOP converter for higher light-load efficiency with selective phase shedding. This increases the average IPOP converter efficiency from 92.5% to 94.1% across the load range of 260 W to 13.6 kW. Peak efficiency is also increased from 93% to 95.5%. In this article, we present a method to optimize the modular SAB IPOP system for high efficiency over a wide load range.

An Active-Bridge based, current-source, three-phase inverter (3PAB) is proposed. It is a single-stage, galvanically-isolated topology, which enables direct interface to a three-phase grid. Operation is similar to a Dual Active Bridge converter, in which the secondary side H-bridge is replaced with a three-phase bridge. A novel modulation technique presented in the paper enables unidirectional power flow from DC to AC side, while energizing all three output phases in one link cycle. Zero voltage, zero-current turn-on of all devices reduces switching losses and increases efficiency. The proposed topology is a viable solution for applications where a compact and lightweight, galvanically-isolated inverter is required such as roof-Top photovoltaic installations.

Increased knowledge of atmospheric water vapor can improve weather predictions and is expected to reduce errors in products derived from GPS and (In)SAR data. At GPS ground stations Integrated Water Vapor (IWV) is estimated from the GPS signal delay with a high temporal resolution. The Envisat MERIS spectrometer obtains spatially dense IWV observations but at limited moments in time. In this research the additional value of MERIS IWV is evaluated when added to GPS IWV for the purpose of obtaining a high quality spatial-temporal water vapor product. At each of 39 stations, first GPS IWV from surrounding stations is used to produce a two months time series of IWV with a temporal resolution of one hour. Then both GPS and MERIS IWV are used together. The two resulting time series are validated against direct GPS IWV as measured at the station.

A tendency to erect ever more wind turbines can be observed in order to reduce the environmental consequences of electric power generation. As a result of this, in the near future wind turbines may start to influence the behavior of electric power systems by interacting with conventional generation and loads. Therefore, wind turbine models that can be integrated into power system simulation software are needed. A model that can be used to represent all types of variable-speed wind turbines in power system dynamics simulations is presented. The modeling approach is commented upon, and models of the subsystems of which a variable speed wind turbine consists are discussed. Some results obtained after incorporation of the model in PSS/E, a widely used power system dynamics simulation software package, are presented and compared with measurements.