This paper is a simple and systematic approaches to the design of sliding mode controller for buck DC-DC Converters. Various aspects of the design, including the practical problems and the proposed solutions, are detailed. However, these control strategies can't compensate for large load current and input voltage variations. In this paper, a new control strategy by compromising both schemes advantages and avoiding their drawbacks is proposed, analyzed and simulated.

Summary The communication links between a satellite and the Earth station (ES) are exposed to many impairments such as noise, rain, and atmospheric attenuations. They are also prone to loss such as those resulting from antenna pointing and polarization. The Algerian Earth Observation satellite AlSat‐1b is designed to accomplish its mission in S‐band (Telecommands and Telemetry) and X‐band (images) frequencies in low Earth orbit (LEO). The ground segment (GS) of this satellite, situated in Oran, Algeria, is based on the X/Y antenna mounting system with 7.3‐m dish diameter. This large reflector can cause antenna pointing errors. The Antenna Control Unit (ACU) implemented in this station can be configured with or without an AutoTrack system. In this work, operational tests and analysis of the different communication links between AlSat‐1b and the ground station are presented. The obtained results clearly show that the quality of the S‐band links can reliably and efficiently satisfy the requirements without the use of the AutoTrack. On the contrary, the use of AutoTrack is necessary in order to obtain an improved level of link quality in the X band.

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