Cyber-physical power system (CPPS) frequency control faces the state estimation error brought by cyber contingencies, such as delay and packet loss. The current CPPS study mainly focuses on resilient observer design against cyber contingencies. The controllability of the cyber contingencies, however, is overlooked. This paper introduces the age of information (AoI) for the observer design of CPPS frequency control. AoI is equipped with the observability and controllability of cyber contingencies. Namely, the AoI model can be used to characterize and alleviate cyber contingencies. Then, the state estimation error is proposed as an AoI penalty function. Next, the packet management and the observer gain are integrated into the design for the AoI penalty function minimization. Finally, a case study is carried out on a single- area CPPS and it shows that the proposed algorithm provides better state estimation accuracy.

The reversible data hiding in encrypted images (RDH-EI) technique has been widely used to achieve privacy protection and convenient management of cloud storage images. The existing RDH-EI methods focus on the embedding capacity, reversibility, and the quality of decrypted images. This paper considers a new performance indicator of RDH-EI, the file size of encrypted images, which directly affects the cloud storage cost of content owner and network transmission efficiency. The goal is to obtain the smallest file size and to vacate sufficient space for data embedding. We propose a multi-MSB compression method that includes three strategies: the iterative MSBs-inversion prediction (IMIP), the adjacent prediction plane XOR (APPX), and the block variable length coding (BVLC). The file size of encrypted images is adaptively minimized while ensuring the format compatibility and lossless reconstruction. An encrypted image is generated by a combination of stream ciphers and bit scrambling to improve the resistance to various attacks such as the cipher-only attack (COA). Experimental results demonstrate that the proposed method has higher embedding capacity and resistance to COA compared with the current state-of-the-art methods for images with different texture complexity. The proposed algorithm can achieve the maximum embedding rate ranging from 0.74 to 4.78 bpp.

Injection of both positive and negative sequence currents is desirable for three-phase voltage source converters under unbalanced grid fault condition. However, the 2ndorder oscillation exists in the positive and negative sequence synchronous reference frame. Several approaches have been reported to cope with this 2ndorder oscillation. In this paper, a simple yet efficient control method in double synchronous reference frame (DSRF) is proposed. The proposed method does not need additional filter or decoupling circuit, and does not require signal reconstruction for the current reference. Theoretical analysis and simulation study show that the proposed control method not only achieve zero steady state error, but also exhibits faster transient response. Experimental results verify the performance of the proposed current control method in DSRF.

In three-phase grid-tied inverter, grid voltage feedforward is helpful to improve grid-tied power quality for strong grid condition. This paper found that the voltage feedforward had different effect on power quality under weak grid condition compared with that in ideal grid condition. And recent reported studies show that grid voltage feedforward has negative effect for grid-inverter system stability. This paper analyzes the voltage feedforward effects on power quality and system stability, and proposes a proportional voltage feedforward scheme to improve system stability and reserve ability to improve power quality under weak grid condition. Then how to design the proportional voltage feedforward scheme is presented. Theoretical and experimental results verify the effectiveness of the proposed control method for improving system stability and power quality under weak grid condition.

As a basic building block, the phase-locked loop (PLL) has been widely used in the grid-connected voltage source inverter (VSI). But it has been shown recently that PLL has adverse impact on stability of grid-inverter system. In a weak grid, the PLL may cause unexpected harmonic, or even instability. In order to overcome this problem, this paper proposes a q-axis voltage feedforward control method to mitigate the impact of PLL. Specifically, the detailed analysis and implementation of proposed method are depicted. Finally, experimental results are presented to verify the proposed method.

This paper proposes a thermal network parameter estimation method to find RC parameters of the Cauer network using cooling curve of IGBT module. The solutions are developed by exploiting the relationship between thermal network parameters and time constants of junction temperature response curves. Experimental tests are performed to validate the accuracy of the developed method. Advantages of the proposed method include no need to know the power loss information of IGBT and no need to heat the IGBT module up to thermal steady-state. Moreover, the proposed method is able to obtain complete RC parameters of the Cauer network. In addition, we show that the identified RC parameters can be used for condition monitoring and junction temperature estimation.

Inshore ship detection from high-resolution satellite images is a useful yet challenging task in remote surveillance and military reconnaissance. It is difficult to detect the inshore ships with high precision because various interferences are present in the harbor scene. An inshore ship detection method based on the weighted voting and rotation-scale-invariant pose is proposed to improve the detection performance. The proposed method defines the rotation angle pose and the scaling factor of the detected ship to detect the ship with different directions and different sizes. For each pixel on the ship template, the possible poses of a detection window are estimated according to all possible pose-related pixels. To improve robustness to the shape-similar distractor and various interferences, the score of the detection window is obtained by designing a pose weighted voting method. Moreover, the values of some parameters such as similarity threshold and the weight of “V” are investigated. The experimental results on actual satellite images demonstrate that the proposed method is invariant to rotation and scale and robust in the inshore ship detection. In addition, better detection performance is observed in comparison with the existing inshore ship detection algorithms in terms of precision rate and recall rate. The target pose of the detected ship can also be obtained as a byproduct of the ship detection.

This paper proposes a color-direction patch sparsity-based image in painting method to better maintain structure coherence, texture clarity, and neighborhood consistence of the in painted region of an image. The method uses super-wavelet transform to estimate the multi-direction features of a degraded image, and combines with color information to construct the weighted color-direction distance (WCDD) to measure the difference between two patches. Based on the WCDD, the color-direction structure sparsity is defined to obtain a more robust filling order and more suitable multiple candidate patches are searched. Then, the target patches are sparsely represented by the multiple candidate patches under neighborhood consistency constraints in both the color and the multi-direction spaces. Experimental results are presented to demonstrate the effectiveness of the proposed approach on tasks such as scratch removal, text removal, block removal, and object removal. The effects of super-wavelet transforms and direction features are also investigated.

In this paper, we present the performance analysis of a self-recovery fragile watermarking scheme using block-neighbor- hood tamper characterization. This method uses a pseudorandom sequence to generate the nonlinear block-mapping and employs an optimized neighborhood characterization method to detect the tampering. Performance of the proposed method and its resistance to malicious attacks are analyzed. We also investigate three optimization strategies that will further improve the quality of tamper localization and recovery. Simulation results demonstrate that the proposed method allows image recovery with an acceptable visual quality (peak signal-to-noise ratio (PSNR) as 25 dB) up to 60% tampering.

In this letter, a texture-preserving despeckling algorithm for synthetic aperture radar images using an evidence framework is proposed. The salient aspects of this approach are given as follows. (1) The maximuma posterioriestimate can be guaranteed to converge to the optima by selecting the Gaussian distribution and Gaussian Markov random field model as the likelihood function and prior model, respectively. (2) MacKay's evidence framework can automatically sustain the balance between speckle reduction and texture preservation. (3) We use the Jeffreys prior to perform the second-level inference of the evidence framework. Experimental results are given to demonstrate the validity of the proposed despeckling method.

This work presents results of our work in development of a genetic algorithm based path-planning algorithm for local obstacle avoidance (local feasible path) of a mobile robot in a given search space. The method tries to find not only a valid path but also an optimal one. The objectives are to minimize the length of the path and the number of turns. The proposed path-planning method allows a free movement of the robot in any direction so that the path-planner can handle complicated search spaces.

This paper presents a new digital watermarking method based on chaotic maps. Different from most of the existing chaotic watermarking methods, two chaotic maps are incorporated into the watermarking system to resolve the finite word length effect and to improve the system's resistance to attacks. One map is used for watermark generation, another as the private key. Simulation results show that the proposed digital watermarking system is feasible and robust to common signal processing procedures. In addition, it performs better than existing watermarking schemes and exhibits better protection than watermarking systems using only one chaotic map

The work presents an automatic and efficient video object segmentation algorithm. Moving object extraction is carried out by adaptive background model and edge-based change detection techniques. The background is updated by use of pixel history and a moving object mask. Connected component analysis and morphological filtering are employed to obtain an accurate VOP (video object plane). Finally, a novel object tracking window scheme is applied to improve the processing speed. Experimental results for three different types of MPEG-4 video sequences are shown to demonstrate the effectiveness of the proposed algorithm.

A relaxation algorithm composed of both a time-step parallel algorithm and a component-wise parallel algorithm is proposed for solving large-scale system simulation problems in parallel. The interconnected nature of the system, which is characterized by the component connection model, is fully exploited by this approach. A technique for finding an optimal number of the time steps is also described. Finally, this algorithm is illustrated via several examples in which the possible trade-offs between the speedup ratio, efficiency, and waiting time are analyzed.