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Power electronic converters in grid applications as for example hybrid transformers are vulnerable to grid faults, so that a protection system is required. This paper identifies critical overcurrents and overvoltages due to grid faults and presents grid models to calculate the overcurrents and a high frequency transformer model to calculate the overvoltages, in order to derive requirements/specifications for designing protection systems., 2021 23rd European Conference on Power Electronics and Applications (EPE'21 ECCE Europe), ISBN:978-1-6654-3384-6, ISBN:978-9-0758-1537-5

This paper deals with a novel hybrid transformer configuration able to face power quality issues occurring on modern distribution grids integrating distributed generation from renewable energy sources and non-linear power electronic loads. The proposed system encompasses a three-phase distribution transformer with secondary windings arranged according to an open-end configuration and a three-phase inverter with floating DC bus. Unlike previous hybrid transformers the proposed one does not require a bidirectional converter to manage bidirectional power flows, neither a tertiary winding to supply the inverter, thus allowing the use of standard MV-LV distribution transformers with simple modifications. The obtained power conversion system can be exploited to perform a voltage control at the distribution grid edge, a reactive power management and harmonic pollution mitigation. Simulations confirm the effectiveness of the proposed solution, ensuring high power quality voltage control under unbalanced grid and load conditions.

An electrical-balance duplexer achieving the state-of-the-art linearity and insertion loss (IL) performance is presented, enabled by a partially depleted RF silicon-on-insulator CMOS technology. A single-ended configuration avoids the common-mode isolation problem suffered by topologies with a differential low-noise amplifier. Highly linear switched capacitors allow for impedance balancing to antennas with

Microinverter has become a new trend for photovoltaic (PV) grid-tie systems due to its advantages which include greater energy harvest, simplified system installation, enhanced safety, and flexible expansion. Since an individual microinverter system is typically attached to the back of a PV module, it is desirable that it has a long lifespan that can match PV modules, which routinely warrant 25 years of operation. In order to increase the life expectancy and improve the long-term reliability, electrolytic capacitors must be avoided in microinverters because they have been identified as an unreliable component. One solution to avoid electrolytic capacitors in microinverters is using a two-stage architecture, where the high voltage direct current (DC) bus can work as a double line ripple buffer. For two-stage electrolyte-free microinverters, a high boost ratio dc-dc converter is required to increase the low PV module voltage to a high DC bus voltage required to run the inverter at the second stage. New high boost ratio dc-dc converter topologies using the hybrid transformer concept are presented in this dissertation. The proposed converters have improved magnetic and device utilization. Combine these features with the converter's reduced switching losses which results in a low cost, simple structure system with high efficiency. Using the California Energy Commission (CEC) efficiency standards a 250 W prototype was tested achieving an overall system efficiency of 97.3%. The power inversion stage of electrolyte-free microinverters requires a high efficiency grid-tie inverter. A transformerless inverter topology with low electro-magnetic interference (EMI) and leakage current is presented. It has the ability to use modern superjunction MOSFETs in conjunction with zero-reverse-recovery silicon carbide (SiC) diodes to achieve ultrahigh efficiency. The performance of the topology was experimentally verified with a tested CEC efficiency of 98.6%. Due to the relatively low energy density of film capacitors compared to electrolytic counterparts, less capacitance is used on the DC bus in order to lower the cost and reduce the volume of electrolyte-free microinverters. The reduced capacitance leads to high double line ripple voltage oscillation on DC bus. If the double line oscillation propagates back into the PV module, the maximum power point tracking (MPPT) performance would be compromised. A control method which prevents the double line oscillation from going to the PV modules, thus improving the MPPT performance was proposed. Finally, a control technique using a single microcontroller with low sampling frequency was presented to effectively eliminate electrolyte capacitors in two-stage microinverters without any added penalties. The effectiveness of this control technique was validated both by simulation and experimental results. Ph. D.

A new topology is proposed for fully-electronic tap changers in distribution transformers. In every single phase, the voltage is regulated by a 2x1 matrix converter, which can be extended using the concept of multilevel converters. The topology allows reaching the desired functionality with one single tap, which reduces the cost of the transformer.