Photovoltaic Energy Yield Improvement in Two-Stage Solar Microinverters

The focus in this paper is on the two-stage photovoltaic (PV) microinverters using a buck-boost dc/dc front-end converter. Wide input voltage range of the front-end converter enables operation under shaded conditions but results in mediocre performance in the typical voltage range. These microinverters can be controlled with either fixed or variable dc-link voltage control methods. The latter improves the converter efficiency considerably in the range of the most probable maximum power point (MPP) locations. However, the buck-boost operation of the front-end converter results in noticeable variations of the efficiency across the input voltage range. As a result, conventional weighted efficiency metrics cannot be used to predict annual energy productions by the microinverters. This paper proposes a new methodology for the estimation of annual energy production based on annual profiles of the solar irradiance and ambient temperature. Using this methodology, quantification of the annual energy production is provided for two geographical locations

Grid Integration of DC Buildings: Standards, Requirements and Power Converter Topologies

Residential dc microgrids and nanogrids are the emerging technology that is aimed to promote the transition to energy-efficient buildings and provide simple, highly flexible integration of renewables, storages, and loads. At the same time, the mass acceptance of dc buildings is slowed down by the relative immaturity of the dc technology, lack of standardization and general awareness about its potential. Additional efforts from multiple directions are necessary to promote this technology and increase its market attractiveness. In the near-term, it is highly likely that the dc buildings will be connected to the conventional ac distribution grid by a front-end ac-dc converter that provides all the necessary protection and desired functionality. At the same time, the corresponding requirements for this converter have not been yet consolidated. To address this, present paper focuses on various aspects of the integration of dc buildings and includes analysis of related standards, directives, operational and compatibility requirements as well as classification of voltage levels. In addition, power converter configurations and modulation methods are analyzed and compared. A classification of topologies that can provide the required functionality for the application is proposed. Finally, future trends and remaining challenges pointed out to motivate new contributions to this topic

Digest of "Implementation Possibilities of SMD Capacitors for High Power Applications"

Focus is on implementation possibilities of surfacemount device (SMD) to be used in high power applications. SMD capacitors reduce the size and dimensions of a power circuit and increase the flexibility of placement of other components. Ceramic and electrolytic capacitors are compared by means of voltage ripple, volume, labour-intensity and impedance. A 1 kW experimental setup of a quasi-Z-Source inverter (qZSI) based converter was built to compare SMD capacitor performance in the quasi-Z-source (qZS) network. Operation waveforms in both input voltage extremes showed that no significant visual differences exist in the performance of the two types of capacitors.  Differences in voltage ripple were found in the electrolytic and ceramic capacitor case. This fact could be caused by high temperature on the electrolytic capacitors when the voltage ripple damping capability decreases. The heat reduction could be achieved by selecting capacitors with smaller impedance and higher permissible ripple current. If labour intensity and price are not essential, then SMD ceramic capacitors can be recommended for high power applications. Electrolytic capacitors could be implemented only in the case of paralleling them in order to reduce total impedance