Sharif Digital Repository

Complex systems are omnipresent and play a vital role in in our every-day lives. Adverse behavior of such systems has generated considerable interest in being able to control complex systems modeled as networks. Here, we propose a topology-dynamics-based approach for controlling complex systems modeled as networks of coupled multi-dimensional dynamical entities. For given dynamics and topology, we introduce an efficient scheme to identify in polynomial time a finite set of driver nodes, which – when endowed with the control function – steer the network to the desired behavior. We demonstrate the high suitability of our approach by controlling various networked multi-dimensional dynamics,... 

The electric assist control strategy is one of the well-known methods for managing the power sources of hybrid electric vehicles. Because of the dependence of the electric assist control strategy approach on its parameters, optimization of this strategy can improve its performance, which results in lower fuel consumption and lower emission levels. However, one of the main concerns about optimization of this strategy is its dependence on the driving behaviour. This paper aims to propose a new control strategy based on the electric assist control strategy with a smaller number of control parameters and less dependence on the driving behaviour. This strategy is usable only for vehicles equipped... 

Power management strategies play a key role in the design process of hybrid electric vehicles. Electric Assist Control Strategy (EACS) is one of the popular power management strategies for hybrid electric vehicles (HEVs). The present investigation proposes a new framework to advance the EACS. Dynamic Programming method is applied to an HEV model in several drive cycles, and as a result, some optimal operating regions are found. The obtained regions are almost distinct, and consequently, some threshold lines can be defined to separate them. The obtained threshold lines are used to eliminate some parameters of the EACS to reduce its sensitivity to the driving behavior. It is shown that by... 

In this paper a new post fault operation strategy is proposed for modular multilevel converter (MMC). The conventional MMC fault tolerant operation methods use redundant cells in spinning or cold reserve schemes, however in this work the MMC fault tolerant operation is achieved without requiring any redundant cells. The introduced strategy modifies capacitors reference voltages and arms modulation reference waveforms in faulty leg of MMC while other legs operate normally. The applied technique leads to having some degree of overvoltage in faulty leg capacitors which could be neglected since the number of cells is high. Simple realization and significant economic savings would be attained as... 

One of the primary challenges of re-planning in high-speed urban railways is the randomness of disruptive events. In this study, an integrated disturbance recovery model presented in which short-turn and stop-skip service operations are optimized together to minimize the average of passengers’ waiting times. This study develops a discrete-event simulation model that employs a variable neighborhood search algorithm to maintain the service level under infrastructure elements’ unavailability. Due to the unpredictable nature of the incidents, the uncertainty associated with obstruction duration is experimentally analyzed through probabilistic scenarios. The computational experiments are... 

One of the primary challenges of re-planning in high-speed urban railways is the randomness of disruptive events. In this study, an integrated disturbance recovery model presented in which short-turn and stop-skip service operations are optimized together to minimize the average of passengers’ waiting times. This study develops a discrete-event simulation model that employs a variable neighborhood search algorithm to maintain the service level under infrastructure elements’ unavailability. Due to the unpredictable nature of the incidents, the uncertainty associated with obstruction duration is experimentally analyzed through probabilistic scenarios. The computational experiments are... 

In this paper, optimal control strategy is applied to parallel three-phase inverters using SVPWM technique. The three-phase system is transformed to a synchronous-stationary frame, suitable cost functions are defined, and the switching schemes are determined for the inverters. The control strategy minimizes the circulating current between the inverters, therefore, proper load sharing scheme is achieved. Simulations are performed for steady state and load change operation, and the results which show the suitability of the controller are provided. ©2009 IEEE  

Anaerobic digestion (AD) is a green technology that has been applied for many years. One of the main problems in this process is controlling these bioreactors to maximize methane production. A supervisory control strategy has been proposed to improve the methane production rate in an anaerobic digestion process while minimizing the risk of process failure in the presence of several drastic feedstock changes. The inner loop consisted of a feedback control that manipulated the feed flow rate for achieving the desirable methane production rate. A rule based control strategy was used as supervisory control loop. This controller received the total volatile fatty acids concentration in the reactor... 

In this paper, we try to interpret "Duality of Dynamic Locomotion and Dynamic Object Manipulation". Since our main goal in this paper is to offer the duality concept and to validate it with a case study, we deal with the problem in a simple and abstract system. As a case study, we describe the duality between the problem of 2D dynamic object manipulation of a sphere using two planar manipulators and 2D dynamic locomotion of lower part of a biped robot. Having obtained the equations of dynamic object manipulation, we change the boundary conditions of the problem in such a way that both radius and mass of sphere object tend to infinity. Simultaneously, both of size and mass of manipulators'... 

This article proposes two novel approaches to improve the superimposed frequency droop scheme for the control of dc microgrids (MGs). Conventional voltage-based control strategies suffer from issues such as undesirable voltage regulations, poor power sharing among the sources, and negative effects of line resistances on the equivalent droop characteristics. To overcome these challenges, a superimposed frequency droop scheme has been introduced. However, this method suffers from three major issues: 1) instability in terms of load variation, which is due to the location of system dominant poles; 2) limitation in system loading due to the limitation in the transferred reactive power; and 3)... 

Societal concerns over global warming issues and dependence on fossil fuels have caused the vehicle market share of plug-in hybrid electric vehicles (PHEVs) to grow. A large penetration of PHEVs, however, would likely put higher stress on power systems. To lessen the PHEVs' harmful impacts on the distribution grid, this paper proposes a two-stage charging control strategy modeled on a renewable-based energy hub. In the first stage, a home-based charging control method is formulated in which the charging cost of PHEVs is considered as an objective. Running this procedure by PHEV schedulers in houses, in the second stage of the proposed strategy, the PHEV coordinator agent (PCA) applies a... 

In this study, control strategies based on time-varying LQR, Lyapunov-Floquet transformation (LFT), backstepping, feedback linearization, and constant gain feedback control are implemented for the linearized time periodic equations of spacecraft relative motion when the reference orbit is elliptic. Also, natural and nonnatural leader-follower two-spacecraft formations are studied. The stability of the closed-loop response, the control effort required, and the settling time are investigated and compared for all control strategies. Furthermore, using constant gain feedback, the estimated region of attraction of the closed-loop system is obtained analytically  

Racing catamarans use aerodynamic alleviation concept which in existing extreme ground effect significantly enhances the performance. Beside design measures, controlling strategies may be employed as convenient solutions to improve the performance and address concerns regarding poor stability in these crafts. Being of substantial importance for a racing catamaran to reach the final speed as soon as possible, this study attempts to find the optimal form of changing the drive angle (as control variable) to minimize its acceleration time. In this regard, a mathematical model is developed for forward acceleration phase of these catamarans based on empirical and theoretical methods. Then the... 

A 3 DOF platform was constructed in the Georgia Institute of Technology to perform new control strategies in an experimental framework. Also in this simulator, there isn't any sensor used by a real satellite for attitude determination. The setup was structured on data transmitting and synchronization of distributed elements for ADCS tests. In such a plan, not only can different elements of the test bed be used individually, but also they can support an integrated hardware in the loop test. Accordingly, reusing the hardware sources causes a cost reduction of development. Furthermore the geometric interferences of different parts are minimized in this plan. So, the test bed can be developed...