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Aiming at the leakage current problem of single-phase transformerless photovoltaic(PV) grid-connected inverters, the recent proposed topologies are classified and reviewed. These topologies are divided into half-bridge type and full-bridge type. The topology characteristics of transformerless PV inverter are analyzed. This paper presents some of transformerless PV inverter topologies and discusses the evolution laws among various topologies to clarify the interrelationship between them. Furthermore, according to the evolution laws, a new topology is proposed. Finally, Simulations and experiments compare leakage current suppression capability of the proposed topology, H5 topology and HERIC topology. [ABSTRACT FROM AUTHOR]

A new nonlinear compact LED model is presented in this paper. The model is useful in the design stage of LED driver system. The parameter extraction procedure is presented step by step. Since the power of a single LED unit is very low, manufacturers often arrange LED units in the form of an array named LED module. On the basis of theoretical I-V characteristic curve of the LED module, the electrical performance of LED module can be tested according to the rated parameters provided by its manufacturers. Five fitting methods are used to obtain the fitting curves. The sum of squares due to error (SSE) and the coefficient of determination (R-square) are compared to choose a better fitting curve. Six terms gaussian fitting method, which has optimal fitting performance among the five methods, is chosen to construct the nonlinear mathematical model of the LED module, and then the simulation model is built with MATLAB/Simulink. A Boost converter simulation circuit adapts this model, and a 25 W dimming prototype is designed to verify the validity of the model. The simulation and test results show that the error of the model is small, and it meets the requirements of practical application. [ABSTRACT FROM AUTHOR]

Infragravity waves (IGWs) play a crucial role in nearshore hydrodynamics and are the primary drivers of coastal hazards such as harbor resonance and overtopping over seawalls. Field observations show that during five storm events in Fall 2013, the IGW heights at the landward side were significantly larger than those at the seaward side of an isolated shoal near Cape Canaveral, Florida, USA. The concurrent offshore incident waves were energetic with directions nearly perpendicular to the shoal. The maximum wave height-to-depth ratio was below 0.3, indicating no wave breaking. Here, we propose a semi-analytical model in combination with field observations to investigate the shoal-induced increase in the cross-shoal IGW energy flux. The model was proposed based on the theory of spatial evolution of nonlinear energy transfer from primary waves to IGWs over an idealized trapezoidal topography under nonbreaking conditions, and was calibrated using a numerical dataset of 21 test cases generated by the non-hydrostatic numerical wave model Simulating Waves till SHore (SWASH). The predicted increase in the cross-shoal IGW energy fluxes are in reasonable agreement with field observations, with 78 % data variability explained by the model. Also, the IGW energy flux increase calculated from the observed IGW height increase was found to coincide with the observed IGW energy flux increase in the cross-shoal direction. The results strongly indicate that the observed amplification of IGWs near Cape Canaveral in Fall 2013 is largely attributed to the topography-induced nonlinear energy transfers from sea-swells to IGWs. [ABSTRACT FROM AUTHOR]

Predicting wave runup on reef-fringed coasts using phase-resolving modelings suffers from uncertainty induced by wave randomness, spectral-width determination, and reef-surface-roughness reproduction. A multi-layer non-hydrostatic model SWASH was first validated against two physical experiments and then applied to simulate runup over coral reefs. Simulations with different wave sequences for the same wave condition indicated that infragravity swash (R IGW) variability was the main contributor to the extreme runup (R 2 %) uncertainty. R IGW was positively correlated to the off-reef incident-wave groupiness factor and the average number of waves per wave group, suggesting that prior knowledge of incident group structure could help in reducing the uncertainty of runup prediction. In ensembles with 100 simulations of different random wave sequences, the ratio of R 2 % with 5% exceedance level to R 2 % with 95% exceedance level decreased with increasing number of spectral components and approached to 1.15–1.3 with over 600 components. Runup uncertainty induced by randomly phasing did not significantly vary with spectral widths and reef-surface roughness. Runup uncertainty due to arbitrarily specifying reef-surface roughness was much more significant than the uncertainty induced by wave randomness and spectral width, suggesting that accurate reproduction of reef surface roughness has a high priority in physical and numerical modelings. • Uncertainty in runup prediction is considerable over fringing reefs. • Variability in infragravity-frequency swash is a primary source for the uncertainty. • The uncertainty reduces with incident waves generated using more frequency bins. • Incident wave-group height and length affect the infragravity-frequency swash height. • Accurate reproduction of reef surface roughness has a high priority. [ABSTRACT FROM AUTHOR]

The lifetime of traditional light-emitting diode (LED) drivers is mainly affected by electrolytic capacitor. Therefore, a single-stage isolated electrolytic capacitor-less LED driver is proposed, with which the electrolytic capacitor is eliminated and the output current ripple is reduced. Firstly, the operation principle and switching mode of the topology are analyzed. Then, the feasibility of the topology is analyzed by using the state space average method. Finally, an experimental prototype of 60 W output power is built to verify the correctness of the scheme. [ABSTRACT FROM AUTHOR]

The lifetime of light-emitting diode (LED) drivers is mainly affected by electrolytic capacitors. Therefore, it is necessary to eliminate electrolytic capacitors from LED drivers. Firstly, basic concept of LED driver without electrolytic capacitors is addressed in this paper. Then, a new electrolytic capacitor-less LED driver is proposed and its operation principles are analyzed in detail. In order to achieve better control effect, model predictive control (MPC) strategy is introduced in this topology. Following that, the mathematical model of the circuit which adopts MPC is derived. Finally, simulations and experiments on a 24 V, 3A laboratory prototype are carried out to verify the feasibility of the proposed topology and control strategy. [ABSTRACT FROM AUTHOR]

Widespread flooding of reef-fringed islands demonstrates the insufficient protection provided by reef topographies and suggests the necessity of artificial structures for hazard prevention and mitigation. As an indicator of the structural protection efficiency, the wave overtopping rate is difficult to estimate in reef environments because hydrodynamics over reefs violate the application conditions of standard overtopping formulas. A combined physical and numerical modeling was performed to investigate wave transformations over reefs of different topographies and overtopping at vertical seawalls on the reefs. Results showed that, in addition to the off-reef wave height and still water level, the off-reef wave period also played significant roles. The intensity of short-wave motions and the level of wave setup near the seawall were positively correlated with the off-reef wave period, and the intensity of infragravity-wave motions depended largely on it. Steeper fore-reef slopes would lead to more intensive wave motions and higher setup on reef flats and, consequently, higher overtopping rates. Furthermore, the overtopping rate exponentially decreased with the distance between the seawall and reef edge, primarily due to the decay of short waves in the surf zone. • A laboratory experiment on random wave transformation and overtopping in reef environments was conducted. • The ability of SWASH model was validated against the experimental data. • Installation of a seawall on a reef flat could significantly modify the wave field. • Influences of hydrodynamic and reef topography on the physical drivers of flooding were studied. [ABSTRACT FROM AUTHOR]