Aiming for converters with high efficiency and high power density demands converter topologies with zero-voltage switching (ZVS) capabilities. This letter shows that in order to determine whether ZVS is provided at a given operating point, the stored charge within the mosfets has to be considered and the condition LI ² ≥2Q _oss has to be fulfilled. In the case of incomplete soft switching, nonzero losses occur which are analytically derived and experimentally verified in this letter. Furthermore, the issue of nonideal soft-switching behavior of Si superjunction mosfets is addressed.

The strings of photovoltaic panels have a significantly reduced power output when mismatch between the panels occurs, as, e.g., caused by partial shading. With mismatch, either the panel-integrated diodes are bypassing the shaded panels if the string is operated at the current level of the unshaded panels, or some power of the unshaded panels is lost if the string current is reduced to the level of the shaded panels. With the implementation of dc-dc converters on panel level, the maximum available power can be extracted from each panel regardless of any mismatch. In this paper, different concepts of PV panel-integrated dc-dc converters are presented and their suitability for panel integration is evaluated. The buck-boost converter is identified as the most promising concept and an efficiency/power density ( η- ρ) Pareto optimization of this topology is shown. Based on the optimization results, two 275 W converter prototypes with either Silicon MOSFETs with a switching frequency of 100 kHz or gallium nitride FETs with a switching frequency of 400 kHz are designed for an input voltage range of 15 to 45 V and an output voltage range of 10 to 100 V. The theoretical considerations are verified by efficiency measurements which are compared to the characteristics of a commercial panel-integrated converter.

The rising electricity demand of data centers has initiated a development trend towards highly efficient power supplies. Therefore, a multi-cell converter approach for a telecom rectifier module breaking through the efficiency and power density barriers of traditional single-cell converter systems is presented in this paper. The potential of the multi-cell approach for high efficiency is derived from fundamental scaling laws of different system performance aspects in dependence of the number of converter cells and the benefits of the interleaving technique. Based on the available degrees of freedom in the design of such a converter system, a comprehensive multi-objective optimization of the entire system with respect to efficiency and volume is performed with detailed component loss and volume models. In order to verify the analytical models and the design procedure, a hardware demonstrator of a 3.3kWmulticell 230VAC/48VDC telecom power supply with Ncells = 6 isolated converter cells in an input-series output-parallel (ISOP) arrangement is presented with measurement results indicating a maximum efficiency of η = 97.7% and a power density of ρ = 2.2kW/dm³(= 36W/in³). Furthermore, different paths for future performance improvements of the multi-cell arrangement are outlined.

The increasing demand for higher power densities and higher efficiencies in power electronics, driven by the aerospace, electric vehicle and renewable energy industries, encourages the development of new converter concepts. In particular, modular and/or multi-level (M/ML) topologies are employed to break the performance barriers of state-of-the-art power converters by simultaneously reducing the system losses and volume/weight. These improvements mainly originate from the replacement of high voltage transistors, typical of two-level converters, with low voltage, e.g. 200V, devices, offering superior electric performance. Hence, two low on-state resistance silicon (Si) and gallium nitride (GaN) 200V power semiconductors are comprehensively characterized in this paper to support the multi-objective optimization and the design of M/ML power converters. First, the selected devices are analyzed experimentally determining their conduction, thermal and switching characteristics; for this purpose, a novel ultra-fast transient calorimetric measurement method is introduced and explained in detail. In the course of this analysis, an unexpected switching loss mechanism is observed in the Si devices at hand; the physical reason of this behavior is clarified and it is proven to be solved in next generation research samples, which are also characterized by measurements. Finally, the influence of the measured power semiconductors performance on the overall efficiency and power density of a typical converter is determined through a case study analyzing a hard switching half-bridge operated as single-phase inverter, i.e. the fundamental building block of several M/ML topologies. It is concluded that, in this voltage and power class, GaN e-FETs are nowadays approximately a factor of three superior to Si Power MOSFETs; however, the better heat dissipation achieved by the latter still makes them the preferred solution for higher power applications.

Due to the increasing electricity demand of data centers driven by the emergence of cloud computing and big data, the focus on the development of telecom and data center power supplies is shifted towards high efficiencies. In this paper, a multi-cell converter approach for a telecom rectifier module breaking through the efficiency and power density barriers of traditional single-cell converter systems is shown. The comprehensive optimization of the entire system with respect to efficiency and volume is described and the applied component loss models are explained. Furthermore, the design of a hardware demonstrator based on the optimization results is presented and several important design aspects are explained in detail.