Percorrer por autor "Chen, Liping"
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- Analysis and implementation of fractional-order chaotic system with standard componentsPublication . Yao, Juan; Wang, Kunpeng; Huang, Pengfei; Chen, Liping; Machado, J. A. TenreiroThis paper is devoted to the problem of uncertainty in fractional-order Chaotic systems implemented by means of standard electronic components. The fractional order element (FOE) is typically substituted by one complex impedance network containing a huge number of discrete resistors and capacitors. In order to balance the complexity and accuracy of the circuit, a sparse optimization based parameter selection method is proposed. The random error and the uncertainty of system implementation are analyzed through numerical simulations. The effectiveness of the method is verified by numerical and circuit simulations, tested experimentally with electronic circuit implementations. The simulations and experiments show that the proposed method reduces the order of circuit systems and finds a minimum number for the combination of commercially available standard components.
- Analysis of a rectangular prism n-units RLC fractional-order circuit networkPublication . Chen, Liping; Wu, Xiaobo; Xu, Linpeng; Lopes, António M.; Machado, J. A. Tenreiro; Wu, Ranchao; Ge, SuoliangIt was demonstrated recently that ideal capacitors can not exist physically and that the behavior of real-world inductors and capacitors is characterized by fractional-order (FO) models. Therefore, the modeling and analysis of FO electrical circuit networks (FO-ECN) has gained considerable interest. This paper introduces the basic principles of a class of rectangular prism n-units () RLC FO-ECN, including the mathematical modeling and the analysis of the impedance magnitude and phase. Three general formulas of the equivalent impedance between two nodes of the FO-ECN are obtained by the matrix transform method. The relationship between the impedance and the FO-ECN parameters, including the capacitance, inductance, number of circuit units and FO are investigated. Numerical simulations reveal dynamical phenomena not exhibited by ordinary ECN.
- Design and implementation of grid multi-scroll fractional-order chaotic attractorsPublication . Chen, Liping; Pan, Wei; Wu, Ranchao; Machado, J. A. Tenreiro; Lopes, António M.This paper proposes a novel approach for generating multi-scroll chaotic attractors in multidirections for fractional-order (FO) systems. The stair nonlinear function series and the saturated nonlinear function are combined to extend equilibrium points with index 2 in a new FO linear system. With the help of stability theory of FO systems, stability of its equilibrium points is analyzed, and the chaotic behaviors are validated through phase portraits, Lyapunov exponents, and Poincaré section. Choosing the order 0.96 as an example, a circuit for generating 2-D grid multiscroll chaotic attractors is designed, and 2-D 9x9 grid FO attractors are observed at most. Numerical simulations and circuit experimental results show that the method is feasible and the designed circuit is correct.
- Double color image encryption based on fractional order discrete improved Henon map and Rubik’s cube transformPublication . Chen, Liping; Yin, Hao; Yuan, Liguo; Machado, J. A. Tenreiro; Wu, Ranchao; Alam, ZeeshanA double color image encryption method based on DNA (deoxyribonucleic acid) computation and chaos is proposed. Differently from the conventional algorithms, double color images are encrypted at the same time so that we can save information of each other, which makes the encryption more safe and reliable. In addition, a new chaotic fractional order (FO) discrete improved Henon map (FODIHM) is proposed as a pseudo-random number generator. To ensure the plain-image sensitivity of the encryption algorithm, the initial value of FODIHM is calculated from the hash value of the color image (SHA-256) and from the three additional keys entered by the user. Furthermore, a Rubik’s cube transform scrambles the pixels in each color component of the two images. Then, each pixel in each color component of the two images is diffused by means of different DNA coding rules. Finally, the CAT transform, based on FO discrete Logistic map and the classic XOR, is used to further improve the security performance. The key space size of the proposed algorithm is of order 10 135, which is about 30 orders of magnitude higher than those available in the literature. The information entropies are 7.9974 and 7.9973, which are very close to the ideal entropy value of 8. The values of the unified average changing intensity (NPCI) are 99.630 and 99.623, while the number of pixels change rate (UACR) are 33.473 and 33.553, which are also close to the ideal NPCR and UACR value of 99.6094 and 33.4635, respectively. The numerical results and security analysis prove that the algorithm has good resistance to several classic attacks.
- Improved Decentralized Fractional PD Control of Structure VibrationsPublication . Xu, Kang; Chen, Liping; Wang, Minwu; Lopes, António M.; Machado, J. A. Tenreiro; Zhai, HouzhenThis paper presents a new strategy for the control of large displacements in structures under earthquake excitation. Firstly, an improved fractional order proportional-derivative (FOPD) controller is proposed. Secondly, a decentralized strategy is designed by adding a regulator and fault self-regulation to a standard decentralized controller. A new control architecture is obtained by combining the improved FOPD and the decentralized strategy. The parameters of the control system are tuned using an intelligent optimization algorithm. Simulation results demonstrate the performance and reliability of the proposed method.
- Variable coefficient fractional‐order PID controller and its application to a SEPIC devicePublication . Chen, Liping; Chen, Gang; Wu, Ranchao; Lopes, António M.; Machado, J. A. Tenreiro; Niu, HaihongThe fractional-order proportional–integral–derivative (FOPID) controller has two more parameters than the integer-order proportional–integral–derivative (PID). Such characteristic makes the controller design more flexible and leads to superior performance. This study proposes a variable coefficient FOPID (VCFOPID) with optimal single step parameters, combining discrete synthesis and variable control parameters. The new algorithm is compared with previous FOPID discrete methods via several examples. Since the energy losses of the single-ended primary-inductor converter (SEPIC) cannot be ignored, the standard models are insufficient and a new model is derived using quantum-behaved particle swarm optimisation. The VCFOPID is applied to the SEPIC and both the effectiveness of the controller and the model are verified experimentally.
- A variable-order fractional proportional-integral controller and its application to a permanent magnet synchronous motorPublication . Chen, Liping; Chen, Gang; Li, Penghua; Lopes, António M.; Machado, J. A. Tenreiro; Xu, ShuiqingThe time-domain approximation of the Grünwald–Letnikov fractional derivative is intuitive and widely adopted in the design of fractional-order proportional-integral (FOPI) controllers. To solve the accuracy reduction caused by truncating the series, an optimized discrete FOPI is presented. The effectiveness of the new FOPI is highlighted and compared with the one exhibited by a controller implemented based on the Oustaloup method. Furthermore, to improve the performance of the FOPI, a variable-order fractional proportional-integral (VFPI) controller is proposed. The response of the VFPI is verified in the control of a permanent magnet synchronous motor. Simulation and experimental results show the superior performance of the VFPI.