This paper will revise, experimentally investigate, and discuss the main application challenges related to gallium nitride power semiconductors in switch-mode power converters. Gallium Nitride (GaN) devices are inherently gaining space in the market. Due to its high switching speed and operational switching frequency, challenges related to the circuit design procedure, passive component selection, thermal management, and experimental testing are currently faced by power electronics engineers. Therefore, the focus of this paper is on low-voltage (<650 V) devices that are used to assemble DC-DC and/or DC-AC converters to, for instance, interconnect PV generation systems in the DC and/or AC grids. The current subjects will be discussed herein: GaN device structure, the advantages and disadvantages of each lateral gallium nitride technology available, design challenges related to electrical layout and thermal management, overvoltages and its implications in the driver signal, and finally, a comprehensive comparison between GaN and Si technology considering the main parameters to increase the converters efficiency.

Low Voltage DC microgrids emerge as a viable alternative to AC microgrids. A large research interest is noted towards fast and selective protection of DC grids, typically focusing on hybrid or full solid state solutions. In this paper, the use of fuses as short-circuit protection in Low Voltage DC microgrids is evaluated. The main advantage of fuses is that they are simple, cheap, standardized and have low steady state losses. A theoretical basis is formed to model DC short-circuit currents in grids with a limited short-circuit availability. The outcomes are applied to evaluate the possibilities of fuse protection in LVDC grids. It was found that fuses are an effective means of protection, although the required amount of capacitance at the output of the voltage balancing converter can be high, which impacts the total system cost. A fuse based protection strategy is presented that highlights the need for additional capacitance to clear faults compared to the necessary capacitance for system stability. An experimental setup was built to validate the claims.

Since building-integrated photovoltaic (BIPV) modules are typically installed during, not after, the construction phase, BIPVs have a profound impact compared to conventional building-applied photovoltaics on the electrical installation and construction planning of a building. As the cost of BIPV modules decreases over time, the impact of electrical system architecture and converters will become more prevalent in the overall cost of the system. This manuscript provides an overview of potential BIPV electrical architectures. System-level criteria for BIPV installations are established, thus providing a reference framework to compare electrical architectures. To achieve modularity and to minimize engineering costs, module-level DC/DC converters preinstalled in the BIPV module turned out to be the best solution. The second part of this paper establishes converter-level requirements, derived and related to the BIPV system. These include measures to increase the converter fault tolerance for extended availability and to ensure essential safety features.

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Reliability of DC-DC converters is important in photovoltaic (PV) applications like building integrated PV systems, where the module-level converter may be stressed significantly. Understanding and predicting the most failing components with accurate degradation models in such systems enables the design for reliability. In this paper, a photovoltaic mission profile-based reliability analysis framework is proposed where the inputs and models of the framework can be adjusted according to the converter topology, the components and the failure mechanisms under investigation. The framework is demonstrated by comparing the influence of two different one-year mission profiles on the solder joint degradation of a MOSFET in an interleaved boost converter. This is done by using an electro-thermal circuit simulation in PLECS and a finite element MOSFET model in COMSOL. In future work, the mesh and the geometry of the solder joint can be adjusted to more closely match the practical stress-cycle (S-N) curve used to determine the lifetime. This framework allows for exploring more accurate models or even simplify parts with low sensitivity in order to obtain a thorough understanding of their accuracy and to determine the overall converter reliability.

As compared to two-wire, unipolar DC microgrids (DCμGs), bipolar DCμGs apply a positive, neutral and negative conductor to increase the power transfer capability while retaining two voltage levels for supplying low-and high-power devices at an appropriate voltage. However, connecting devices between the positive or negative pole and the neutral conductor will result in unbalanced currents causing voltage to unbalance. Therefore, power electronic converters with voltage balancing capability are essential. Instead of installing dedicated voltage balancing converters, this study proposes to apply three-level DC-DC converters. These converters can interface battery storage with bipolar DCμGs and balance the pole-to-neutral voltages at the same time. However, high levels of unbalanced currents drive three-level DC-DC converters towards their theoretical unbalanced operating limits. To derive these, a method is presented which decomposes the governing equations in balanced and unbalanced components. Although the method is generally applicable to the three-level converters, the full-bridge threelevel converter serves as a comprehensive example. The method enables to derive the unbalanced operating area of threelevel DC-DC converters and to appropriately size the filter inductor. Furthermore, a novel modulation strategy is introduced in order to lower the inductor current ripple in unbalanced conditions, supported by experimental results.

Building-integrated photovoltaics (BIPV) is seen as a key technology to reduce the environmental impact and net power consumption of buildings. The integration of PV into building components, such as façade, window, roof or shading elements, leads to a distributed generation over the building envelope with a profound impact on the electrical installation. Designing the electrical system with string inverters and a possible wide variety of module sizes and technologies is a challenging task. To overcome this issue, Module-Level Converters (MLCs) can be used. A supplementary benefit is that the consequences of partial shading can strongly be reduced. This paper investigates whether the current generation of MLCs is suited for embedment in facade BIPV modules. The PV output is categorized and compared to the input parameters of the converters. Besides the discrepancy between the physical dimensions of the converters and the desired installation location, thermal and electrical measurements on a prototype BIPV curtain wall element reveal that daily energy losses can be as high as 50% due to thermal overload when used in a moderate climate such as Belgium. The paper concludes by discussing further standardization of BIPV module-level converters.

In this paper, a family of interleaved high-stepdown (I-HSD) DC-DC converters is proposed integrating the Valley-Fill switched capacitor structure and a double series capacitor Buck converter. This integration generates three converters, which will be extensively explored herein via theoretical and experimental analysis. A complete theoretical analysis of the structures is presented in order to mathematically explain the physical operation of the proposed topologies. A design procedure is presented for the following specifications: 300 V/12 V input to output voltage, 100 W of power and a switching frequency of 100 kHz and the results obtained are compared to state-of-theart DC-DC converters that enable similar high step-down operation.