مجله کنترل
سال چهارم شماره 2 (تابستان 1389)

In this work we use directional enlargement of domain of attraction to increase critical clearing time of nonlinear systems. To find the optimal control parameters, we use measure theory which converts the enlargement problem to a linear programming problem. At first step we find the critical directions of system, along them the system instability happens. After that we find optimal controlling parameters to extend domain of attraction along directions of interest. The efficiency of the proposed method is verified in simulation part for increasing critical clearing time of a power system with four machines.

In this paper, a PI guidance law is proposed to nullify the LOS rate. Stability of the guidance dynamics including autopilot and seeker dynamics is analyzed by employing circle criterion. Stability conditions give an analytical bound for the time of the flight up to which stability can be assured. The stability bound of the new guidance law is less conservatism than PN guidance law. Also, this approach can be used as a tool for Guidance, Autopilot and seeker parameters design. Simulation results show the effectiveness and robustness of the proposed guidance law against maneuvering target as compared to PN.

Safe grasping and handling delicate object with fingertips need a sophisticated control algorithm capable of position and force control in one direction. Most of position-force control algorithms proposed so far divide the work space of manipulators into two subspace and control position in one subspace and force in the other one. Meanwhile, for safe grasping purpose we should apply force at minimum necessary level which itself is not a known quantity during motion, so the desired value of normal force is not known forehand. This paper propose a new positionforce algorithm and employ that to accomplish pinching and moving delicate object with two multilink fingers. Performance issues and parameters robustness with respect to friction coefficient is also addressed. Several numerical examples are provided to show versatility of the proposed method.

In this paper, nonlinear model of a hydraulic actuator considering amplitude and rate saturations is identified. First actuator model with a first order transfer function and nonlinear functions of saturation with unknown parameters are taken in account, then by defining two suitable destination functions and numerically optimization of them, unknown parameters are estimated. Introduced model appropriately has described the nonlinear behavior of the actuator and has higher accuracy due to conventional linear models. Comparison between nonlinear simulation results using new model and the experimental tests, show the fidelity of this model. This model has large applications in flying systems autopilot designing, also it could be used as the costly real actuators in simulation laboratory.

Power Market, due to unique characteristics of power system, can not be considered as a competitive market. It is much more like an oligopoly market where small numbers of Generation Companies (GenCos) compete to supply the market demand. It became more obvious in 1990s and 2001 as some major crisis hit power markets around the globe. In such a situation, the ability of market participants could raise prices over the competitive level. On the other hand, there is also possible GenCos collude and as a result the market prices rise. The ability of raising the price in collusion is highly dependent on price elasticity of demand. In this paper, at first several reported recent research works related to the collusive behavior in the power market are reviewed. Then, an analytic model based on game theory is proposed to analyze the behavior of participants in competitive and collusive market states. Using the proposed model on a simple system, variation of the market price in both competitive & collusive states are investigated and effects of price elasticity on equilibrium point in a collusive state are studied. Furthermore, the numerical results obtained from the proposed collusion model and a monopolistic model of the market, are compared and the differences are interpreted.

A new method is presented in this paper to improve the performance of time delay Multiple-Input Multiple-Output systems. The method uses a specific compensator for each of the control loops by which the non-minimum phase characteristic of the open loop functiondchanges to minimum phase. When using the proposed added compensator for robustness of the system it is sufficient that compensater becomes dominant gain with respect to the upper norm of the uncertainty of the process. The proposed method is applicable easily in a convetional feedback control loop.