Ibrahim Mustafa Mehedi

State feedback with fractional integral control design based on the Bode’s ideal transfer function

State feedback technique through a gain matrix has been a well-known method for pole assignment of a linear system. The technique could encounter a difficulty in eliminating the steady-state errors in some states. Introducing an integral element can effectively eliminate these errors. State feedback with fractional integral control is proposed, in this work, for pole placement of a linear time invariant system. The proposed method yields simple gain formulae. The paper presents the derivation of the design formulae. The method is applied to stabilise an inherently unstable inverted pendulum-cart system. Simulation and experimental results show the effectiveness of the proposed method for set-point tracking, disturbance rejection and stabilising the inverted pendulum. Comparison with the results obtained from applying Achermann’s formula is also presented.

Fractional-order controller design for a heat flow process

In this paper, fractional-order controller designs for integer first-order plus time delay systems are investigated. Based on Bode’s ideal transfer function as a reference model, a new structure of the fractional-order controller is proposed. The internal model control principle is used to design the controllers. The effectiveness of the controllers is demonstrated through simulations and their efficiency is validated through experimentation on a heat flow platform.

Tandem organic solar cells with improved efficiency

Tandem solar cell provides an effective way to improve power conversion efficiency of organic solar cell by combining two or more organic solar cells. Each cell has different absorption maximum and width so it provides the amenities of using the photon energy more effectively. Due to the limited absorption band of organic materials, single junction organic solar cells suffer from low efficiency. Here, we demonstrate the performance of single layer devices based on the solution of carrier continuity equation in MATLAB. Polymers P3HT:PCBM, pBBTDPP2:PCBM and PCDTBT:PCBM provide power conversion efficiency of 3%, 3.15% and 6.2% respectively. Hence series connected tandem cell P3HT:PCBM as front cell and pBBTDPP2:PCBM as rear cell is designed to achieve higher efficiency where the proposed model gives the power conversion efficiency of 6%. A major back through came when the front cell is replaced by PCDTBT:PCBM solar cell in the device configuration which provides the power conversion efficiency of 8.8%, till now the maximum efficiency for organic solar cell.

Performance analysis of P3HT:PCBM based organic solar cell

An analytical model of the photocurrent-voltage characteristics has been utilized to analyze important properties of organic bulk-heterojunction solar cells, e.g., generation rate, electron current density, hole current density and the total photocurrent density. The generation rate of P3HT:PCBM based solar cell critically depends on the absorption coefficient. For measuring the electron and hole current density solution of carrier continuity equation is used in MATLAB. Then the effects of electron and hole current density on the performance of P3HT solar cells have been studied. The result of this paper demonstrate that current density due to electron plays a major role in photocurrent production while hole current density has a very little impact. Effect of electron and hole mobility variation are investigated separately which indicate that increasing electron mobility are extremely important than hole mobility to increase the power conversion efficiency of P3HT:PCBM blend. The dependence of electron and hole current densities as a function of the blend thickness is also analyzed.

Time Varying Back Propagating Algorithm for MIMO Adaptive Inverse Controller

In the field of automatic control system design, adaptive inverse is a powerful control technique. It identifies the system model and controls automatically without having prior knowledge about the dynamics of plant. In this paper neural network based adaptive inverse controller is proposed to control a MIMO system. Multi layer perception and back propagation are combinedly used in this investigation to design the NN learning algorithm. The developed structure represents the ability to identify and control the MIMO system. Mathematical derivation and simulation results for both plant identification and control are shown in this paper. Further, to prove the superiority of the proposed technique, performances are compared with recursive least square (RLS) method for the same MIMO system. RLS based adaptive inverse scheme is discussed in this paper for plant identification and control. Also the obtained simulated results are compared for both plant parameter estimation and tracking trajectory performance.

Theoretical investigation of Gibb's free energy and phase diagram for In x Ga 1−x N nano-film system

The models for investigating the phase diagram of InGaN thin films have been anticipated by considering the effects of strain energy, the self-energy of misfit dislocations and surface energy to Gibbs free energy. Total Gibbs free energy varies with Indium composition and thickness of the epitaxial thin film. The calculated results indicate that over critical thickness, energy of the films increases with increasing thickness. The phase diagrams of InGaN films grown on GaN substrate have been calculated. There is a small effect of surface energies of solid phases on the phase diagrams of epitaxial film. With increasing the thickness of InGaN films the wurtzite phase is found to be decreased. This is due to the increase of thickness, misfit dislocations and the commencing of phase separation. Accurate information of InGaN nano film is applicable for the innovation of III-nitride based nano-electronics system.

Moon Landing Trajectory Optimization

Trajectory optimization is a crucial process during the planning phase of a spacecraft landing mission. Once a trajectory is determined, guidance algorithms are created to guide the vehicle along the given trajectory. Because fuel mass is a major driver of the total vehicle mass, and thus mission cost, the objective of most guidance algorithms is to minimize the required fuel consumption. Most of the existing algorithms are termed as “near-optimal” regarding fuel expenditure. The question arises as to how close to optimal are these guidance algorithms. To answer this question, numerical trajectory optimization techniques are often required. With the emergence of improved processing power and the application of new methods, more direct approaches may be employed to achieve high accuracy without the associated difficulties in computation or pre-existing knowledge of the solution. An example of such an approach is DIDO optimization. This technique is applied in the current research to find these minimum fuel optimal trajectories.

Effect of dislocation density on the performance of InGaN-based MJ solar cell: Analytical approach

In this study the effect of dislocation density on the performance of InGaN based multi junction solar cell has been calculated analytically. It is found that dislocation density adversely affects the open circuit voltage, short circuit current density and conversion efficiency of a solar cell. Efficiency is found to be improved with the increase in the number of junction (24.4-43.56% for single-six junction solar cells) while considering no dislocation. Whereas it is found that the efficiency is affected when dislocation density (1001-1013m-2) is incorporated for analyzing the performances of either single junction (24.47-8.25%) or multi junction solar cell (43.56-15.25% for six junctions). The effect of dislocation density on minority carrier life time is also been anticipated in this study.

Estimation of minority carrier lifetime in InGaN single junction solar cell

The parameters that influence the performance of solar cell, minority carrier lifetime is a crucial one. The increase of minority carrier lifetime results in higher conversion efficiency. Minority carrier lifetime is determined and analyzed for InGaN single junction solar cell at different excess carrier concentrations by considering the effect of radiative, Auger, Shockley-Read-Hall (SRH) and surface recombination. Since InGaN is a direct bandgap material it is found that radiative recombination is the dominating mechanism for determining the minority carrier lifetime.