This paper presents dynamic analysis and nonlinear control of laterally mass varying combat aircraft based on a six degree-of-freedom model derived for a variable mass system. The objective is to investigate the effects of asymmetric lateral mass variation, due to mass ejection, from two different perspectives-the open loop dynamic behavior through bifurcation analysis; and the closed loop control performance while carrying out some demanding maneuvers. Bifurcation analysis reveals considerable coupling between the longitudinal and lateral-directional channels even for a modest lateral shift in the center-of-mass due to store ejection, which in turn is observed to give rise to a spiral-dive like divergent mode even at low angles-of-attack. Thereafter, the well-known high angle-of-attack cobra maneuver is implemented for the symmetric center-of-mass case using sliding mode control technique and using a new single loop control formulation in contrast with the conventional inner-outer loop formulation. The proposed single loop control formulation is further extended to handle the lateral movement of center-of-mass due to asymmetric store ejection using the asymmetric dynamics model proposed and derived in this paper.
This paper addresses the controllability and global stability issues of a magnetically actuated satellite in the geomagnetic field. The variation of the geomagnetic field along the orbit, which is time varying in nature, makes the dynamics of the satellite time varying also. Sufficient conditions for controllability of such a time varying magnetic attitude control system are given. As a major contribution, it is proven that the three-axis controllability of the spacecraft actuated by the magnetic actuators is possible and it does not depend on the initial angular velocity of the spacecraft. Global controllability is a precursor to global stability. Therefore, exponential stability for an arbitrarily high initial angular velocity and an arbitrary initial orientation is proven next for a proportional-derivative control law using averaging theory. It is also proven that even an iso-inertial satellite can be stabilized using the time invariant feedback control, which was hitherto not possible, even using time variant conventional control. Simulation results are presented under different initial orientations and angular velocities of the satellite in the presence of favorable and unfavorable gravity gradient torques to validate the proposed control method.
Summary
This article proposes forecast‐based modeling and robust frequency control strategy in isolated microgrids (MGs) to improve its stability. The intermittency and variability in renewable generation is problem for its smooth integration to MGs considering frequency stability. Continuous rise in penetration levels of renewable energy sources (RESs) is the main motivation behind forecast‐based modeling and controller design for MGs. The disturbances that affect the frequency in the MG may come from the load side and/or the generation sides. In MGs, at the generation side, the forecast of power from RESs is usually obtained to get a rough estimate of available renewable power. The forecasted power always differs from the actual one, so the secondary frequency controller may get overburdened due to forecast error resulting in abnormal frequency deviation that may lead to unstable power system. The proposed H∞ based robust control design considers the forecast error which improves the system stability and performance against disturbances coming from load/generation side. First, a long short term memory based recurrent neural network has been used to forecast the renewable power availability. Thereafter a H∞ controller is designed, and it is shown through extensive simulation studies that the H∞ controller outperforms optimized PID controllers so far as rejecting the effects of uncertainties in RESs, forecasting errors, and model parameter variations are concerned. The proposed robust controller design is also validated with real time simulator (OP4510) made by Opal‐RT. The controller hardware in the loop (CHIL) test has been done taking the simulation time step of 50 μS.
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