Application of VMD and Hilbert Transform Algorithms on Detection of the Ripple Components of the DC Signal

Accurate detection of ripple components of the direct-current (DC) signals is essential for evaluating DC power quality. In this study, the combination algorithm based on variational mode decomposition (VMD) and Hilbert transform (HT) is applied to detect and analyze the characteristics of the ripple components of the DC disturbance signals. Firstly, the optimal modal number of VMD algorithms is comprehensively determined by observing the center frequencies of the mode components and the Index of Orthogonality (IO) of mode components. Through utilizing the VMD algorithm, the DC disturbance signal is accurately decomposed into a series of amplitude modulation-frequency modulation (AM-FM) functions. Then, the HT algorithm is applied to each AM-FM function to obtain the corresponding instantaneous amplitude and frequency, and the characteristics of DC disturbance signal are determined. Some case studies are implemented to analyze the ripple components of the DC disturbance signal with the VMD-HT and empirical mode decomposition (EMD) algorithm. Finally, the experiment results of Gree Photovoltaic Cabin have verified the feasibility and effectiveness of the proposed combination VMD-HT algorithm by comparison with EMD and the window interpolation fast Fourier transform (WIFFT) algorithms

Tone mapping based on fast image decomposition and multi‐layer fusion

To solve the problem of low efficiency and colour distortion in several typical tone mapping operators for high dynamic range (HDR) images, the authors propose a novel tone mapping algorithm based on fast image decomposition and multi‐layer fusion. An input HDR image is firstly decomposed into a base layer and a detail layer by an improved guided filtering method. For the base layer, its dynamic range is compressed by the simulated camera response function. For the detail layer, it is enhanced to produce more fine structures and reduce halo effect by applying the guided image filter. The colour balance correction method is adopted to suppress colour distortion. The experiments on HDR images demonstrate that the proposed technique could bring better brightness, contrast, and visibility with less halo effect than other state‐of‐the‐art methods both qualitatively and quantitatively in most cases