Search

Photovoltaic (PV) inverters form the backbone of PV generation. This paper proposes an all-film-capacitor, transformerless single-phase inverter for PV application. The topology is a combination of a front-end boost stage, a half-bridge (HB) inverter stage, and a buck–boost power decoupling stage. The grid ripple power is decoupled by a large swing of the HB capacitors along with a limited ripple on the dc link, thus reducing the capacitance requirement and converter volume. Being an HB-derived inverter, the high-frequency common mode leakage current through the PV parasitic capacitance is mitigated. Furthermore, the dc-link average is optimally controlled to ensure a higher efficiency over wide operating load and power factor range. To validate its operation, a Silicon Carbide based 1-kVA laboratory prototype is built and closed-loop experimental results are provided at 100/75 kHz switching frequency over wide operating conditions. [ABSTRACT FROM AUTHOR]

Two major challenges in the transformerless photovoltaic (PV) inverters are the presence of common-mode leakage currents, and as in most single-phase converters the need for reliable and compact double-line-frequency power decoupling. In the proposed doubly grounded inverter topology with innovative active-power-decoupling approach, both of these issues are simultaneously addressed. The topology allows the PV negative terminal to be directly connected to the neutral, thereby eliminating the capacitive-coupled common-mode ground currents. The decoupling capacitance requirement is minimized by a dynamically variable dc-link with large voltage swing, allowing an all-film-capacitor implementation. Furthermore, the use of wide bandgap devices enables the converter operation at higher switching frequency, resulting in smaller magnetic components. The topology uses only four switches and potentially enables a high power density solution. The operating principles, design and optimization, and control methods are explained in detail, and compared with other transformer-less, active-decoupling topologies. A 3 kVA, 100/75 kHz single-phase hardware prototype at 400 V dc nominal input and 240 V ac output with a wide range of power factor has been developed using SiC MOSFETs with only 45 μF/1100 V dc-link capacitance. Extensive experimental results from the prototype are presented to validate the concept, design, and superior performance of the proposed topology. [ABSTRACT FROM AUTHOR]

Recently some stator discharge problems in northern America and Europe have greatly brought people?s concerns to the safety of stator coils. Different from the traditional partial discharge (PD) mechanism, the stator damage problem was thought to be probably caused by a newly promoted theory, namely the vibration sparking (VS). It is well known that during the operation of generators there is come voltage on the surface of the conductive coating, usually less than 10 V, but for ageing generators the voltage can be much higher. During vibration of stator bars caused by electromagnetic force, the conductive coating incessantly gets in touch with and disconnects from stator core, which under some circumstances (usually much easier than PD) may result in vibration sparking (VS) in stator slots. According to recent researches about PD, usually a certain high voltage around 200 V or above is needed for most of the gaps in stator slots of which gap distances are between several micrometers to tens of micrometers to have electrical breakdown. However VS can emerge when the gap voltage is only several tens of volts according to the experiment in this paper. In this paper, first of all, by combining two models (promoted by Jackson and Liese) for the first time, principles of VS were studied integratedly, gap voltage and ground current were calculated and verified through experiments. In addition a model platform of VS was built up by which conditions needed for the emergence of VS and characteristics of VS were studied. Finally optimal resistance per square of conductive coating was calculated based on theoretical analysis and experimental results, which can provide advice for manufacturers to greatly restrain the occurrence of VS. [ABSTRACT FROM AUTHOR]