A Novel Location Method for Interline Power Flow Controllers Based on Entropy Theory

As one of the new generation flexible AC transmission systems(FACTS)devices,the interline power flow controller(IPFC)has the significant advantage of simultaneously regulating the power flow of multiple lines.Nevertheless,how to choose the appropriate location for the IPFC converters has not been discussed thoroughly.To solve this problem,this paper proposes a novel location method for IPFC using entropy theory.To clarify IPFC’s impact on system power flow,its operation mechanism and control strategies of different types of serial converters are discussed.Subsequently,to clarify the system power flow characteristic suitable for device location analysis,the entropy concept is introduced.In this process,the power flow distribution entropy index is used as an optimization index.Using this index as a foundation,the power flow transfer entropy index is also generated and proposed for the IPFC location determination study.Finally,electromechanical electromagnetic hybrid simulations based on ADPSS are implemented for validation.These are tested in a practical power grid with over 800 nodes.A modular multilevel converter(MMC)-based IPFC electromagnetic model is also established for precise verification.The results show that the proposed method can quickly and efficiently complete optimized IPFC location and support IPFC to determine an optimal adjustment in the N-1 fault cases.

Analogies Between the Nonlinear Control Problem and the Multi-level Substructural Method

The establishment of the analogy theory between optimal control and computational structural mechanics is based on the linear quadratic control problem in optimal control and the substructural chain theory in structural mechanics.When the nonlinear optimal control problem is treated by the above theory, especially

Structural Optimization of Hatch Cover Based on Bi-directional Evolutionary Structure Optimization and Surrogate Model Method

Weight reduction has attracted much attention among ship designers and ship owners.In the present work,based on an improved bi-directional evolutionary structural optimization(BESO) method and surrogate model method,we propose a hybrid optimization method for the structural design optimization of beam-plate structures,which covers three optimization levels:dimension optimization,topology optimization and section optimization.The objective of the proposed optimization method is to minimize the weight of design object under a group of constraints.The kernel optimization procedure(KOP) uses BESO to obtain the optimal topology from a ground structure.To deal with beam-plate structures,the traditional BESO method is improved by using cubic box as the unit cell instead of solid unit to construct periodic lattice structure.In the first optimization level,a series of ground structures are generated based on different dimensional parameter combinations,the KOP is performed to all the ground structures,the response surface model of optimal objective values and dimension parameters is created,and then the optimal dimension parameters can be obtained.In the second optimization level,the optimal topology is obtained by using the KOP according to the optimal dimension parameters.In the third optimization level,response surface method(RSM) is used to determine the section parameters.The proposed method is applied to a hatch cover structure design.The locations and shapes of all the structural members are determined from an oversized ground structure.The results show that the proposed method leads to a greater weight saving,compared with the original design and genetic algorithm(GA) based optimization results.

Characteristics of the transient thermal load and deformation of the evacuated receiver in solar parabolic trough collector

As a core element in solar parabolic trough collector, the evaluated receiver often runs under severe thermal conditions. Worse still, the transient thermal load is more likely to cause structural deformation and damage. This work develops an efficient transient multi-level multi-dimensional(M2) analysis method to address photo-thermal-elastic problems, thereby estimating transient thermal load and deformation for the receiver:(i) one-dimensional(1-D) thermo-hydraulic model is adopted to determine the transient thermo-hydraulic state,(ii) 3-D finite volume method(FVM) model for the receiver tube is established to obtain the real-time temperature distribution,(iii) 3-D finite element method(FEM) model is employed to make thermoelastic analysis. Based on this M2 method, the typical transient cases are conducted in cold-start, disturbed-operation and regulatedprocess. Three indicators(average temperature of the wall(ATW), radial temperature difference(RTD), circumferential temperature difference(CTD)) are defined for overall analysis of the receiver thermal load. It is found that in the transient process,receivers face response delay and endure significant thermal load fluctuation. The response time for a single HCE(heat collecting element) under lower mass flow rate(1.5 kg s-1) could sustain 280 s. During the cold-start stage(DNI=200 W m-2 to 800 W m-2), the maximum value of CTD in receiver is as high as 11.67℃, corresponding to a maximum deflection of 1.05 cm.When the mass flow rate decreases sharply by 80%, the CTD reaches 33.04℃, causing a 2.06-cm deflection. It should be pointed out that in the cold-start stage and the lower mass flow rate operation for solar parabolic trough collector, alleviating the transient thermal load and deformation is of importance for safely and efficiently running evaluated receiver.

Spectral Analysis for Preconditioning of Multi-Dimensional Riesz Fractional Diffusion Equations

In this paper,we analyze the spectra of the preconditioned matrices arising from discretized multi-dimensional Riesz spatial fractional diffusion equations.The finite difference method is employed to approximate the multi-dimensional Riesz fractional derivatives,which generates symmetric positive definite ill-conditioned multi-level Toeplitz matrices.The preconditioned conjugate gradient method with a preconditioner based on the sine transform is employed to solve the resulting linear system.Theoretically,we prove that the spectra of the preconditioned matrices are uniformly bounded in the open interval(12,32)and thus the preconditioned conjugate gradient method converges linearly within an iteration number independent of the discretization step-size.Moreover,the proposed method can be extended to handle ill-conditioned multi-level Toeplitz matrices whose blocks are generated by functions with zeros of fractional order.Our theoretical results fill in a vacancy in the literature.Numerical examples are presented to show the convergence performance of the proposed preconditioner that is better than other preconditioners.

Multilevel Techniques for the Solution of HJB Minimum-Time Control Problems

The solution of minimum-time feedback optimal control problems is generally achieved using the dynamic programming approach,in which the value function must be computed on numerical grids with a very large number of points.Classical numerical strategies,such as value iteration(VI)or policy iteration(PI)methods,become very inefficient if the number of grid points is large.This is a strong limitation to their use in real-world applications.To address this problem,the authors present a novel multilevel framework,where classical VI and PI are embedded in a full-approximation storage(FAS)scheme.In fact,the authors will show that VI and PI have excellent smoothing properties,a fact that makes them very suitable for use in multilevel frameworks.Moreover,a new smoother is developed by accelerating VI using Anderson’s extrapolation technique.The effectiveness of our new scheme is demonstrated by several numerical experiments.