An extended state observer based fractional order sliding-mode control (ESO-FOSMC) is proposed in this study, with consideration of the strong nonlinear characteristics of a new electro-hydraulic servo system with iso-actuation balancing and positioning. By adopting the fractional order calculus theory, a fractional order proportional-integral-derivative (PID)based sliding mode surface was designed, which has the ability to obtain an equivalent positioning control with fractional order kinetic characteristics. By introducing the integral term into the sliding mode surface, it was found to be beneficial in reducing the steady-state errors, as well as improving the precision of the control system. Also, by using the fractional order calculus to replace the integral calculus, the form of the convergence is improved; the system transfer of energy is slowed down; and the chattering of the system is greatly weakened. The extended state observer was designed to observe the real-time disturbances, and also to generate the compensation control commands which are added to the FOSMC to achieve the dynamic compensation. By means of numerical simulations, the dynamic and static characteristics of the sliding mode control system were compared with those of the FOSMC and ESO-FOSMC. The experimental results show that the ESO-FOSMC system could effectively restrain the external disturbances and achieve higher control precision, as well as better control quantity without chattering. The semi-physical simulations based experimental tests also demonstrated that the proposed ESO-FOSMC outperformed the FOSMC in terms of system robustness and control precision, which could have a stable control of the gun system quickly and accurately.
The control strategy of VSC based multiterminal HVDC system is investigated in this paper. DC voltage feed-forward compensation and the controller configuration of double closed loops based on linearized feedback of the input and the output are applied in the controller design of the converter. By this approach the decoupled control of the active and the reactive power can be realized. Meanwhile, the voltage and the current waveforms at the ac sides of the converters can be improved. Also, multipoint dc voltage control strategy is proposed in this paper, which can improve the ability of the MTDC system to balance the power and enhance the reliability and economics of system operation. Simulation is performed on a VSC-MTDC system with five terminals and the results show that the proposed control strategy has satisfactory dynamic characteristics and the VSC-MTDC system can persist in supplying ac voltage of good quality to sensitive loads during the disturbances.
Antennas are characterized by their gain and effective aperture area, and the coupling between two antennas in 3-D free space is governed by the Friis transmission equation. In this paper, we derive the properties of antennas in 2-D space, and the equivalent coupling equation. This is useful for evaluating surface-wave coupling between antennas that share the same ground plane or substrate. We propose a quantity which is the effective width for surface-wave coupling, and derive its value for an isotropic surface-wave radiator in two dimensions. We also determine the surface-wave directivity for dipole-like modes, which is relevant to many small planar antennas. The total coupling between two coplanar antennas is a combination of surface waves and space waves, and these two components are distinguished in simulations by calculating antenna coupling as a function of distance. Several simple examples are illustrated including patch and monopole antennas on various substrates. Quantifying the effective surface wave width can serve as a useful tool for optimizing the coupling between coplanar antennas.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.