P. Rastgoufard

An Improved Control Algorithm for Active Filters

This paper proposes a new control algorithm resulting in significant advantages toward smooth control of an active filter (AF). The majority of existing feedforward control methods of the AF system result in switching notches (sharp-rising ripples) in the supply current during transitions of stepped waveshaped nonlinear load current. This is due to switching signals for the AF devices, which are obtained by comparison of the sensed and reference currents of the AF. The proposed control algorithm is based on feedback control, wherein, switching signals for the AF devices are obtained by comparing sensed and reference supply currents. This not only eliminates switching notches in the supply currents but also reduces the supply current total demand distortion below the 5% mark recommended by the IEEE-519 standard. A TMS320C31 digital signal processor is used for real-time implementation of the proposed algorithm. To establish its viability and flexibility, the proposed algorithm is also experimented with a laboratory prototype of the AF system made of a reduced number of switches

Line of sight robot navigation toward a moving goal

In this paper, we consider the problem of robot tracking and navigation toward a moving goal. The goals maneuvers are not a priori known to the robot. Thus, off-line strategies are not effective. To model the robot and the goal, we use geometric rules combined with kinematics equations expressed in a polar representation. The intent of the strategy is to keep the robot between a reference point, called the observer, and the goal. We prove under certain assumptions that the robot navigating using this strategy reaches the moving goal successfully. In the presence of obstacles, the method is combined with an obstacle avoidance algorithm. The robot then moves in two modes, the navigation mode and the obstacle avoidance mode. Simulation of various scenarios highlights the efficiency of the method and provides an instructive comparison between the paths obtained for different reference points.

Power system voltage stability and security assessment

Abstract The purpose of this investigation is to review the recent research progress in voltage stability and security assessment of power systems. This paper presents the fundamental concepts of voltage stability, gives a short recall of the classical voltage theory and different criteria currently available for predicting voltage collapse problems in power systems, which have been associated with multiple power flow solutions, bifurcation, dynamics of tap changers, stochastic loads, singular values, etc. The various methods for studying voltage collapse are compared. The application of expert system techniques to assist in the decision-making process of the reactive power/voltage control problem of power systems and future research directions towards voltage stability and security assessment will also be proposed in this paper.

A new topology of active filter to correct power-factor, compensate harmonics, reactive power and unbalance of three-phase four-wire loads

This paper proposes a new topology of an active filter (AF) with improved control algorithm. The reactive power theory of three-phase circuits is used to obtain reference currents as control quantities for the AF. The developed improved control algorithm is first tested with a standard topology of the AF, thereafter, extended to control a new topology of four-pole AF system. The new topology of the AF system is capable to compensate harmonics and reactive power, correct power-factor and unbalance in three-phase four-wire balanced/unbalanced linear/nonlinear loads. The proposed new topology of the AF system fully compensates neutral current for nonlinear unbalanced load connected in a three-phase four-wire supply system, thereby preventing heating and bursting of neutral conductor. The new topology of the AF system is free from shoot through fault and exhibits a desired performance. The developed control algorithm is implemented using a TMS320C31 DSP system and performance of new topology of the four-pole AF system with improved control algorithm is simulated. Simulation as well as experimental results are given and discussed in detail.

Multi-robot hunting behavior

In this paper we consider the problem of hunting an unpredictably moving prey using a group of robots. We elaborate a mathematical model for the tracking-navigation problem based on geometric rules. This model consists of systems of two differential equations describing the relative motion of the prey with respect to the robots. The control laws are decentralized and the robots move in different modes, namely: navigation-tracking mode, obstacles avoidance mode, cooperative collision avoidance, and circle formation. In the tracking-navigation mode, we use the deviated pursuit strategy, which consists of a closed loop control law based on geometric rules. The properties of this strategy are explored briefly. For obstacles and cooperative collision avoidance, a collision cone approach is used. Our method is illustrated using simulation.

Parallel navigation for reaching a moving goal by a mobile robot

In this paper, we present a method for robot navigation toward a moving object with unknown maneuvers. Our strategy is based on the integration of the robot and the target kinematics equations with geometric rules. The tracking problem is modeled in polar coordinates using a two-dimensional system of differential equations. The control law is then derived based on this model. Our approach consists of a rendezvous course, which means that the robot reaches the moving goal without following its path. In the presence of obstacles, two navigation modes are integrated, namely the tracking and the obstacle-avoidance modes. To confirm our theoretical results, the navigation strategy is illustrated using an extensive simulation for different scenarios.

Computational voltage stability assessment of large-scale power systems

Abstract The problem of voltage instability occurring in power systems and various voltage instability indicators proposed in the literature are reviewed in this paper. A voltage stability margin in terms of the active power that the system can supply before voltage instability occurs is proposed. Two voltage stability assessment programs, one developed by EPRI, the Voltage Stability Analysis Program (VSTAB), and the Voltage Eigen Value Analysis Program (VEVA) developed at Tulane University, are compared. The output of these programs as applied to the IEEE 30-bus test system is tabulated.

DSP based control method of active filter: elimination of switching ripples

This paper deals with a DSP based implementation of a three-phase shunt active filter (AF) to compensate harmonics and reactive power of nonlinear loads. A three-phase diode bridge rectifier with R-L and R-C loads is taken as the nonlinear load. It is observed that the AF systems suffer from the problems of switching ripples and these ripples contribute considerably to the total harmonic distortion (THD) in the supply current. This investigation proposes a new, cost free and simple approach for the elimination of switching ripples. A PWM current controlled voltage source inverter (CC-VSI) is used as the AF. In current controlled VSI two types of PWM techniques, namely, carrierless (hysteresis) and carrier based techniques are used. Two types of current control techniques, namely, direct current control and indirect current control are designed to obtain PWM switching signals for the devices of the AF. A laboratory prototype model of an AF is tested with both the direct and indirect techniques. The capability of the indirect current control technique towards the elimination of switching ripples is established. Experimental results for steady state and transient operating conditions of the AF are given and discussed in detail.

Autonomous navigation and obstacle avoidance using navigation laws with time-varying deviation functions

In this paper we introduce a new family of navigation functions for robot navigation and obstacle avoidance. The method can be used for both path finding and real-time path planning. Each navigation function is composed of three parts: a proportionality term, a deviation function and a deviation constant. Deviation functions are time-varying functions satisfying certain conditions. These functions and parameters are updated in real-time to avoid collision with obstacles. Our strategy uses polar kinematics equations to model the navigation problem in terms of the range and direction between the robot and the goal. The obstacles are mapped to polar planes, and represented by the range and the direction from the robot or the final goal in polar coordinates. This representation gives a certain weight to the obstacles based on their relative position from the robot and facilitates the design of the navigation law. There exists an infinite number of navigation functions obtained by changing the proportionality constant, the deviation constant or the deviation function. This offers an infinite number of possibilities for the robots path. Our navigation strategy is illustrated using an extensive simulation where different navigation parameters are used.

Single-phase switch mode boost rectifier: an improved design/control applied to three phase AC-DC converters to power up telecommunication system

An improved control technique for raising the efficiency and performance of the single-phase switch mode rectifiers is proposed. The switch mode rectifier operates at unity power factor, exhibits negligible harmonies in input current,. and acceptable ripples in DC bus voltage. The topology of single-phase switch mode rectifier considered in this paper uses a main boost converter and an auxiliary boost converter. The main boost converter is switched at a very high frequency to shape the input current close to the sinusoidal and to eliminate the need of an electromagnetic interference (EMI) filter. On the other hand, auxiliary boost converter operates at a very low switching frequency and works as a current deviator as well as current source for DC bus capacitor of the rectifier. The switched mode rectifier has a very simple and autonomous analog control system for the boost converters. For three-phase applications, a modified topology of single-phase switch mode rectifier is proposed. The modified topology of the rectifier unit and its controller can be considered as a switch mode rectifier (SMR) module. In three phase applications, three identical SMR modules either connected in star or in delta can be used. This paper describes the proposed single-phase configurations of switch mode rectifiers. The steady and dynamic performance of the proposed rectifier is analyzed. Simulated results are given and discussed in detail.