Continuous objective-based control for self-optimizing systems with changing operation modes

Flexible heat exchanger network design for chemical processes with operation mode changes

Although various optimization methods for solving single-objective problems have been developed in the last few decades, these methods have lost their eligibility due to the fact that today’s engineering problems are toward multiple objective optimization problems, in real applications. For single-objective optimization problems, for example, in case of a minimization problem, this value is the decision vector giving the smallest objective that can be achieved within the specified constraints. Hence the minimum decision vector within all possible (feasible) solution vectors is the so-called optimal solution and/or optimal design. However, in multi-objective optimization problems, since a different objective value is generated against each decision vector, the superiority of the solutions over each other is determined by considering the trade-off among the objective values. Therefore, the solution of multi-objective optimization problems, unlike single-objective problems, is a set of vectors rather than a single decision vector. In multi-objective optimization problems, especially if there are intricate objectives, the computational cost of the problem increases. In other words, while synchronously trying to maximize one of the objectives and to minimize another one makes it difficult to find the global optimum design. One of the important techniques used in multi-objective optimization problems is Pareto optimality which enables to select the global optimum solution taking into account the trade-off among all objectives. In this context, using of derivative-based methods has decreased, but the use of metaheuristic methods has increased due to the rapid availability of global optimum solution. This is because the improvements in the field of optimization are progressing in proportion to technology and varying according to the needs. In this chapter, one of the recent metaheuristic optimization methods based on swarm intelligence that is so-called a Pareto-based bat algorithm inspired by the behavior of determining the direction and distance of an object using the echo of the sound called the echolocation of bats is used in order to obtain optimum solutions for multi-objective engineering design problems. In this regard, a four-bar planar truss, a real-sized welded steel beam as well as a multi-layer radar absorber are selected as multi-objective engineering design optimization problems. In case the obtained results (optimal designs) are examined, the potency and the reliability of the proposed multi-objective Pareto-based bat algorithm are demonstrated.

A novel control strategy for mode seamless switching of PV converter in DC microgrid based on double integral sliding mode control

Fault detection and diagnosis based on particle filters combined with interactive multiple-model estimation in dynamic process systems

The simple reactor model developed for the fluidized-bed methanator PEDU gives reasonably good parity plots for six PEDU tests using six different catalysts. This model can be used to predict the performance of the pilot plant methanator and as a building block in any computerized simulation of the BI-GAS process for process development, design or optimization purposes. Some refinements could be made to the model to accommodate changes in mode of operation and additional knowledge gained concerning the hydrodynamic properties of the catalyst bed. The kinetic model, based upon a first-order rate equation to describe the catalyst behavior in the PEDU, also appears to be satisfactory as to its utilization in the reactor model. Further refinements could be made to yield a more mechanistically accurate expression, which would include the effects of non-first-order kinetics and deactivation on CO conversion and of selectivity on product distribution. The selectivity of molybdenum-containing catalysts for the water-gas shift reaction has been shown to be significantly higher than that of cobalt-containing catalysts. This suggests that catalysts containing molybdenum might be more suitable for processes in which the water-gas shift reaction must be combined with methanation. However, this increase in selectivity appears to be coupled withmore » a reduction in overall activity. Further investigation is neededto determine whether this reduction is real or merely the result of an imbalance between particle size and pore structure of the molybdenum-containing catalyst, which has resulted in mass-transfer limitations in those catalysts tested so far.« less

Improvement of the Reliability Graph with General Gates to Analyze the Reliability of Dynamic Systems That Have Various Operation Modes

To remove the influence of operation mode changes in the chemical process, the whole variable set is partitioned into external, main, and quality variables. External variables are related to the operation mode. Two regression models are initially developed between external variables and main variables/quality variables, based on which the influence of the operation mode is removed from both input and output of the soft sensor. Then, an additional regression model is constructed for soft sensing, which is robust to the change of the operation mode. Compared to existing methods, the new method has advantages to handle two critical issues: (1) capable of quality estimation in new process modes; (2) able to distinguish changes in operation modes from process faults. Besides, a monitoring and analysis strategy is proposed for performance evaluation of the new soft sensor. Two case studies are provided to illustrate the efficiency of the proposed method. © 2013 American Institute of Chemical Engineers AIChE J, 60: 136–147, 2014

Bioprocessing has been transitioning from batch to continuous processes. As a result, a considerable amount of resource was dedicated to optimising strategies for continuous production. However, the focus has been on developing a suitable and scalable perfusion strategy with little attention given to the selection of optimal cell clones. Cell line development and lead clone selection are critical to bioprocess development. The screening and selection process is typically performed in stages. Microwell plates (MWP) are used to narrow down the number of clone candidates, which will undergo further selective screening in progressively larger small-scale bioreactors (12mL-3L) to identify the top clone for GMP production. Perfusion mode is typically applied at bench-scale for optimisation purposes, while process development and cell clone screening studies at mL-scale still commonly use fed-batch methods. The change of operation mode from bolus feeding to perfusion with a regular exchange of medium, leads to questions regarding the reliability and fit of initial clone selection. Is the early-stage clone ranking impacted by the discrepancy in the operation mode, and does this potentially result in the exclusion of cell clones suitable for perfusion processes? To address this question, we evaluated various CHO cell clones expressing two antibody products using MWP methodologies in fed-batch and semi-perfusion mode. We assessed growth, metabolic, and productivity performance, and ranked cell clones using two different strategies. The first strategy evaluated clones based on a single parameter: the cell-specific productivity (qP). The second considered a collection of multiple parameters using the metric of the Manufacturability index (MICL). Both ranking strategies showed an impact of operation mode and perfusion rate on the clone ranking. Notably, depending on the chosen operation mode, different sets of candidate clones might have been selected for further, more extensive screening. Additionally, we evaluated the reproducibility of our results demonstrating consistency in cell clone growth performance and ranking.

This paper is about the numerical solution of multiobjective optimization problems in continuous spaces. The problem is to define a search direction and a dynamical adaptation scheme for sets of vectors that serve as approximation sets. Two algorithmic concepts are compared: These are stochastic optimization algorithms based on cooperative particle swarms, and a deterministic optimization algorithm based on set-oriented gradients of the hypervolume indicator. Both concepts are instantiated as algorithms, which are deliberately kept simple in order to not obfuscate their discussion. It is shown that these algorithms are capable of approximating Pareto fronts iteratively. The numerical studies of the paper are restricted to relatively simple and low dimensional problems. For these problems a visualization of the convergence dynamics was implemented that shows how the approximation set converges to a diverse cover of the Pareto front and efficient set. The demonstration of the algorithms is implemented in Java Script and can therefore run from a website in any conventional browser. Besides using it to reproduce the findings of the paper, it is also suitable as an educational tool in order to demonstrate the idea of set-based convergence in Pareto optimization using stochastic and deterministic search.

Micro‐grid which connects with the main grid can operate under the grid‐connected mode or the islands mode. During the switching process between the two operation modes, if the control strategy is not complete, there will be problems such as the AC bus voltage oscillation and current surge, which will result in the switchover failure. An improved energy storage inverter control method based on operation states tracking is adopted for the optical storage micro‐grid using master–slave control, which solves the problem of control variables mutation. Secondly, an improved software phase‐locked method based on grid phase state tracking is proposed in an energy storage inverter. The problem of instantaneous mutation of the phase angle is solved by cooperating with the micro‐grid operation state control signal during operation mode changes. Through the improvement of the two control strategies above, the transient shock phenomena of the micro‐grid voltage and current during the switching process is obviously improved, and the harmonic content of the AC voltage and current is obviously reduced. Finally, a detailed model of optical storage micro‐grid is established in MATLAB/Simulink, and the correctness and practicability of the improved control strategy are verified by simulation.

When the power system is disturbed or the operation mode is changed, the electromagnetic transient process will occur, which will lead to the high frequency transient component and affect the protection and control of the power system. Therefore, attention should be paid to the analysis of high-frequency transient components when modeling and analyzing the system model. In view of the fact that the symmetrical-component theory is not suitable for asymmetric transmission lines and the phasor method is not suitable for transient analysis and calculation, this paper uses the phase coordinate approach and Laplace transform to derive the node voltage equation of three-phase π type transmission lines in frequency domain, which can be used to calculate the transient response of transmission lines caused by the change of operation mode or disturbance. And vectorized NILT is used to calculate the time domain solution, which greatly improves the calculation speed. The calculated results are basically consistent with those of ATP-EMTP, and can fully reflect the transient characteristics. This method lays a foundation for analyzing the influence of high frequency transient components on power system and fault analysis considering transient process.

The reversible pump turbine (RPT) is a suitable machine to meet fluctuations in the energy market. The usage of RPTs for this purpose will increase the number of operational mode changes of the machine. In order to reduce the response time of the machine, fast transitions in the mode of operation are desired. Therefore, increased knowledge of how the machine operates during these fast transitions is needed. This paper presents measurements done both at the NTNU Waterpower Laboratory and Tevla Pump Power Plant. The two machines are not geometrically similar, and part of the result focus on the similarities in the measurements despite the differences in the two RPTs. Tevla is owned by the Norwegian company Nord-Trøndelag Energi (NTE) and consists of two reversible pump turbines. The installed capacity is 50 MW. The focus is on the pressure pulsations during the fast transition from pump to turbine mode of operation. Results from both the laboratory and field measurements show few but high pressure amplitudes during the fast transition.

42 V electrical power systems are on their way to replacing the present 14 V systems in automobiles and 42 V/14 V dual voltage systems have been proposed to provide backward compatibility with the existing components for the 14 V system. The synchronous buck/boost converter is an attractive topology for 42 V/14 V dual voltage systems since it offers bi-directional operation without additional components. In this paper, transient currents generated during converter startup or changes in operation modes between buck and boost are analyzed and a cost effective solution to remove the transient currents is proposed. The validity of the proposed control strategy is investigated through simulations and experiments

The effect of different carrier lifetimes on the forward I-V characteristics of a MOS-controlled thyristor (MCT) has been studied using numerical simulation. Those physical mechanisms that have a strong effect on the forward operation of the MCT have been identified and taken into account. The results show that in the design tradeoff between the switching speed and forward current capability there exists a characteristic lifetime below which the operation mode changes from thyristor-like to IGBT-like, and in the transfer between them a region of differential negative resistance exists. >

대용량 화력발전 보일러 과열기와 재열기 튜브는 과열에 취약하여 보일러 정지 시 튜브 내부의 산화 스케일 두께를 측정하여 과열상태를 평가한다. 산화스케일 두께측정에 의한 튜브 온도예측은 튜브의 발췌가 불가피하고 정확한 과열지점의 선정과 튜브의 초기운전온도가 확보되지 못하면 유의한 튜브온도예측결과를 얻을 수 없는 문제점이 있다. 또한 해석적 방법에 의해 튜브 온도를 예측하는 경우 튜브 외부 연소가스에 대한 연소, 복사, 대류 및 난류유동에 대한 방대한 해석이 필요한 반면 순시적인 부하의 변동, 탄종의 변화 및 운전방법의 변화를 반영할 수 없으므로 지속적인 튜브의 온도를 예측할 수 없는 단점이 있다. 본 논문에서는 보일러 운전정보와 유로망 해석을 통해 튜브의 열유속을 계산하고 이를 이용하여 단시간에 튜브의 온도를 예측할 수 있는 기법을 제시하였다. 본 기법을 Larson-Miller Parameter 법과 같은 실용적인 튜브 손상평가기법과 결합하면 유용한 고온손상감시의 수단으로 활용이 가능할 것으로 판단된다.