Sharif Digital Repository

The subject of modeling and stability analysis of dc-dc resonant converters is still a challenge. The conventional large signal nonlinear model of the resonant converter is derived using the sinusoidal approximation and averaging followed by linearization about an operating point. Models obtained with such method involve considerable approximation, and produce results that are limited for higher performance designs. Therefore, it is essential to investigate the stability of the resonant converters using a more sophisticated model. Because of semiconductors switching, dc-dc resonant converters are intrinsically hybrid systems consist of discrete input and continuous states. The complexity of... 

Resonant converters are hard nonlinear systems which are comprised of both continuous and discontinuous nonlinearities. Many nonlinear modeling approaches lead to a very awkward, unsystematic stability analysis and controller design. Hence, stability analysis and stabilizing controller design of the popular LLC resonant converter still remain challenging as direct consequences of the absence of a "systematic modeling". In this paper, the LLC resonant converter is modeled in the form of Piece-Wise Affine (PWA) systems and a Direct Piece-Wise Affine (DPWA) model of the DC-DC LLC resonant converter is proposed. No dynamic is omitted in the modeling approach, and accordingly, the proposed... 

Control and stabilisation of the resonant converters are essential problems in power electronics. The conventional model of the dc-dc series resonant converter (SRC) is derived using the sinusoidal approximation and generalised averaging followed by linearisation about an operating point. This model involves considerable approximation and is not applicable for large variation of load and supply voltage. The authors have already proposed a direct piece-wise affine (DPWA) modelling and control approach for the SRC that operates above resonant frequency. However, the DPWA technique is not applicable to an SRC that operates below resonance because of the presence of harmonics. In this study, a... 

The control and stabilization of resonant converters are essential problems in power electronics. The conventional controller design and stability analysis for these converters are based on the linearized averaged model. Nevertheless, the state variables in resonant converters have large ac variations and the validity of the linearized average model is violated. Hence, using large signal and nonaveraged models are necessary for controller design and stability analysis. In this paper, a new hybrid controller is presented that is applicable to dc-dc series resonant converters and use neither averaging nor small signal approximation. The dc-dc resonant converters are inherently switched affine... 

A dc-dc resonant converter has the advantage of overcoming switching losses and electromagnetic interference which are the main limitations of high frequency power converters. Nevertheless, the modeling and stability analysis of dc-dc resonant converters are considerably more complex than pulsewidth modulation counterparts. The conventional averaged linearized model of the resonant converter has limitations due to averaging and linearization. First of all, the linearized model has large modeling error in presence of large variations of reference voltage and input voltage. Furthermore, Converging area for stabilizing controllers is smaller in the averaged model. In order to overcome these... 

In this work, the effects of rolling parameters, cooling media, and deformation path on mechanical properties and aging behavior of hot-rolled AA2017 were studied. First, hot-rolling experiments were conducted under different working conditions, and the rolled strips were then aged at room temperature for up to 57 days during which hardness and tensile tests were carried out to record the changes in the mechanical properties of the alloy. Furthermore, due to the importance of static recrystallization on subsequent aging behavior, the rate of recrystallization was also computed. To this end, a mathematical model was developed to predict thermomechanical responses during hot rolling using the... 

In the context of the care crisis in modern medicine, the existential needs of patients are not sufficiently satisfied. One idea to address the crisis is that physicians should be educated to be virtuous. This suggestion is inadequate because it does not take into account the role of (non-)human factors, including technologies. The paper focuses on online caring forums, arguing that they are technological factors that can play the role of “focal things”, in which the members gather together to do a care-related focal practice. We study empirically the online forums of Ninisite, a popular Persian website on pregnancy, childbirth, and parenting, and suggest that these forums shape focal... 

Thermal performance of a novel sintered wick heat pipe was investigated in this study. Two types of sintered wick heat pipes were fabricated and tested at different filling ratios of water, and their thermal resistances in different modes were compared. In the first type, wick was sintered annularly (conventional type), and in the other one (novel type of sintered wick) it was sintered only in one third of cross-section. Results showed that dry-out occurs at higher heat input by an increase in the filling ratio. Moreover, the best filling ratio is 20% for both heat pipes. Thermal resistances of the partly sintered wick heat pipe are approximately 28%, 17% and 47% lower than those of the... 

Heat pipes are important cooling devices that are widely used to transfer high heat loads with low temperature differences. In this paper, thermal performance of a novel type of sintered-wick heat pipe, namely, partly sintered-wick heat pipe, was investigated. The heat pipe was filled with degassed water and acetone, as working uids, and effects of filling ratio, orientation, and heat inputs were tested. Moreover, conditions at which dryout occurred were presented. The results showed that the best filling ratio for both working uids is about 20%. The heat pipe filled with water has better thermal performance than that filled with acetone; thus, the thermal resistances of the 20% water-filled... 

In this paper, a novel moving object modeling suitable for multicamera correspondence is introduced. Taking into consideration the color and motion features of foreground objects in each independent video stream, our method segments the existing moving objects and constructs a graph-based structure to maintain the relational information of each segment. Using such graph structures reduces our correspondence problem to a subgraph optimal isomorphism problem. The proposed method is robust against various resolutions and orientations of objects at each view. Our system uses the fuzzy logic to employ a human-like color perception in its decision making stage in order to handle color inconstancy... 

A mathematical model was developed to assess thermomechanical behavior of work rolls during warm rolling processes. A combined finite element analysis-slab method was first developed to determine thermal and mechanical responses of the strip being rolled under steady-state conditions, and then, the calculated roll pressure and temperature field were utilized as the governing boundary conditions for the thermomechanical problem of the work roll. Finally, the thermomechanical stresses within the work rolls were predicted by a thermoelastic finite element approach. The results of the model indicate that, in warm strip rolling, thermal and mechanical stresses developed in the work rolls are... 

Ethylene dichloride thermal cracking is one of the conventional methods for hydrogen chloride production. A critical issue concerned with this method is to provide thermal energy for cracking reaction, which is generally provided by the flammable gasses inside the furnace. Utilizing renewable energy sources can be an interesting topic in this case. Hence, in this paper, the thermal integration feasibility of an ethylene dichloride cracking unit with a hybrid renewable plant, based on geothermal and wind energies, is investigated, while the case study for wind turbines system (Alstom ECO 74/1670/ Class II model) is Meshkin Shahr, located in Iran. To utilize geothermal energy, a...