Component reallocation and system replacement maintenance based on availability and cost in series systems

Component reallocation(CR)is receiving increasing attention in many engineering systems with functionally interchangeable and unbalanced degradation components.This paper studies a CR and system replacement maintenance policy of series repairable systems,which undergoes minimal repairs for each emergency failure of components,and considers constant downtime and cost of minimal repair,CR and system replacement.Two binary mixed integer nonlinear programming models are respectively established to determine the assignment of CR,and the uptime right before CR and system replacement with the objective of minimizing the system average maintenance cost and maximizing the system availability.Further,we derive the optimal uptime right before system replacement with maximization of the system availability,and then give the relationship between the system availability and the component failure rate.Finally,numerical examples show that the CR and system replacement maintenance policy can effectively reduce the system average maintenance cost and improve the system availability,and further give the sensitivity analysis and insights of the CR and system replacement maintenance policy.

A novel technique for the optimal design of offshore wind farm electrical layout

The design of electrical layout is a key element in the offshore wind farm planning.We present a novel electrical layout design optimization method for offshore wind farms in this paper.The proposed method can be used to generate the network model based on fuzzy c-means(FCM)and binary integer programming(BIP)methods.It can automatically allocate wind turbines to the nearest substations and obtain the topology structure of cables utilized to connect wind turbines or turbine and substation.The objective of this optimization is to minimize the investment costs of cable connection and the transmission power losses.The results of case study clearly demonstrated the feasibility of the proposed method and showed that it can be used as a reliable tool for electrical layout design of offshore wind farms.

Approximation Algorithms for Discrete Polynomial Optimization

In this paper,we consider approximation algorithms for optimizing a generic multivariate polynomial function in discrete(typically binary)variables.Such models have natural applications in graph theory,neural networks,error-correcting codes,among many others.In particular,we focus on three types of optimization models:(1)maximizing a homogeneous polynomial function in binary variables;(2)maximizing a homogeneous polynomial function in binary variables,mixed with variables under spherical constraints;(3)maximizing an inhomogeneous polynomial function in binary variables.We propose polynomial-time randomized approximation algorithms for such polynomial optimizationmodels,and establish the approximation ratios(or relative approximation ratios whenever appropriate)for the proposed algorithms.Some examples of applications for these models and algorithms are discussed as well.

Weak bus-constrained PMU placement for complete observability of a connected power network considering voltage stability indices

Phasor measurement units(PMUs)are preferred for installation at weak buses in a power network.Therefore,the weak buses need to be located and the strategic locations of PMUs identified to ensure network observability.Thus,the primary aim of this work is to identify the placements of the maximum number of PMUs installed at the weak buses in the electrical network.The voltage collapse proximity indicator,line stability index,fast voltage stability index,and a new voltage stability indicator utilizing load flow measurement are used to determine the weak buses.A novel deterministic methodology based on a binary-integer linear programming model is then proposed to determine the optimal locations of PMUs.The effect of a single PMU outage considering the weak buses is also demonstrated.The effectiveness of the developed approach is tested and validated on the standard IEEE 14-,118-,300-,and New England 39-bus systems.The obtained results are also compared to those using different weak bus methodologies.