Search results for "Control theory"
showing 10 items of 1333 documents
Oscillation dynamics of free vortex surface in uncovered unbaffled stirred vessels
2016
Abstract The main feature of unbaffled stirred tanks is the highly swirling liquid motion, which leads to the formation of a central vortex on the liquid free surface, when the vessel is operated without top-cover (Uncovered Unbaffled Stirred Tanks, UUST). One of the main drawbacks of such vessels, that limits their industrial applicability, is the possible onset of low-frequency sloshing of the free surface. In this work, original data on oscillation dynamics in UUST are presented. In particular, data focus on the oscillation amplitude as well as on their frequency. Data were obtained by means of a novel experimental technique based on digital image analysis. The effect of impeller geometr…
Robust Control Allocation for Spacecraft Attitude Stabilization under Actuator Faults and Uncertainty
2014
A robust control allocation scheme is developed for rigid spacecraft attitude stabilization in the presence of actuator partial loss fault, actuator failure, and actuator misalignment. First, a neural network fault detection scheme is proposed, Second, an adaptive attitude tracking strategy is employed which can realize fault tolerance control under the actuator partial loss and actuator failure withinλmin=0.5. The attitude tracking and faults detection are always here during the procedure. Once the fault occurred which could not guaranteed the attitude stable for 30 s, the robust control allocation strategy is generated automatically. The robust control allocation compensates the control …
Rendezvous Guidance Trajectories via Multiple-Subarc Sequential Gradient-Restoration Algorithm
2009
We consider the three-dimensional rendezvous between a target spacecraft in a circular orbit and a chaser spacecraft with an initial separation distance and an initial separation velocity. We assume that the chaser spacecraft has variable mass and that its trajectory is governed by three controls, one determining the thrust magnitude and two determining the thrust direction. We employ the Clohessy–Wiltshire equations, describing the relative motion of the chaser vis-a-vis the target, and the multiple-subarc sequential gradient-restoration algorithm to produce first optimal trajectories and then guidance trajectories for the following problems: P1—minimum time, fuel free; P2—minimum fuel, ti…
Modeling the Sequential Switching Shunt Series Regulator
2005
This letter characterizes, in terms of the bandwidth and limit cycle frequency of its constituent subsystems, the sequential switching shunt series regulator -S/sup 4/R, a high-efficiency, low-mass and volume power cell devised to power the next generation of regulated power buses in telecommunication spacecrafts. Transconductance power source modeling is used to obtain linear and nonlinear models. These are used to establish a design control strategy which involves the dynamic response in large load requirements or at the end of the satellite life. Simulations and experimental results are also given to demonstrate the validity of the model.
Study on Improving the Functional Performance of Linear Motion Systems
2015
In the construction of high performance mechanical transmission with high precision in movement and positioning are used ball screws with preloaded double nuts. Among the factors that influence the performance of these transmissions are friction idle torque and friction load torque. Because, theoretically, the friction idle torque is influenced only by the preload force that loading, the double nut of the ball screw, was experimentally determined dependence of that torque of screw speed. Given the set was determined and exposed in the present work, the relation of dependency, idle friction torque, preload force and screw speed. From the relationship thus obtained can determine the instantan…
Partial stability for specific growth rate control biotechnological fed-batch processes
2004
In this paper, the problem of the specific growth rate control in biological reactions in fed-batch mode is dealt with. It is assumed that only part of the state is measurable on-line, namely biomass and volume. Moreover, no estimation of the specific growth rate is used. An unbounded manifold is tracked using a partial state feedback. Then, techniques for partial stability, i.e., only with respect to part of the variables, are used in order to analyze the problem.
Interior permanent magnet synchronous motors: Impact of the variability of the parameters on their efficiency
2016
In the scientific literature, various authors presented different control strategies aimed to increase the efficiency of the interior permanent magnet synchronous motors. These strategies, starting from a well-known mathematical model of the dynamic behaviour of the motor, are able to reduce the power losses acting on the magnetizing component of the stator current. However, none of the proposed approaches takes into account that, varying the working conditions of the motor, also the values of the parameters, which have an impact on the power losses, can vary. In this paper, therefore, starting from an accurate measurement of the motor characteristics for various values of speed and load, w…
A New Digital Demodulator for Sensorless Control of Electrical Drives with Permanent Magnet Synchronous Motors
2008
This paper deals a new digital demodulator algorithm for sensorless control of interior permanent magnet synchronous motors (IPMS) based on the estimation of speed and rotor angular position. To this aim a signal similar to that generated by a resolver connected to the shaft of the motor is obtained injecting high frequency stator currents. A new digital algorithm has been designed and set up to demodulate the above signal whose implementation can be carried out on the same DSP that processes the whole control algorithm. The proposed demodulator scheme is presented and justified on the theoretic point of view. Simulations results finally validate the effectiveness of the demodulator within …
Contribution to the platoon distribution analysis in steady-state traffic conditions
2014
The traffic flow analysis and the relevant vehicle distribution (“free-moving” or “platooned” vehicles) on highway facilities at uninterrupted flow has always had fundamental importance in Highway Engineering, with special reference to topics like traffic operations, car accidents, road safety and air pollution emissions. In light of this, the study suggests a calculation algorithm as a random test generator to simulate a steady state traffic flow and to provide time headways. Thanks to the outcome produced by numerical simulations, we analysed platoon distributions within traffic flows in a steady-state regime and showed the results of numerical analyses carried out by traffic random proce…
Non-linear digital control improving transient response: Design and test on a multiphase VRM
2010
Multiphase interleaved buck converters are widely used for point of load applications, especially for VRMs. Performance optimization issue often clashes with size and cost requirements thus leading the industrial and academic research to focus on advanced solutions. This paper presents a control technique for multiphase VRMs including two interacting sections: the linear loop implements a PWM peak current mode control and the nonlinear subsystem modifies few linear loop parameters under load transients only. Steady-state performances are affected by the linear control only while dynamic performance optimization is a non-linear algorithm issue. The proposed control system improves the dynami…