Optimal Reactive Power Compensation of Distribution Network to Prevent Reactive Power Reverse

The capacitive reactive power reversal in the urban distribution grid is increasingly prominent at the period of light load in the last years.In severe cases,it will endanger the security and stability of power grid.This paper presents an optimal reactive power compensation method of distribution network to prevent reactive power reverse.Firstly,an integrated reactive power planning(RPP)model with power factor constraints is established.Capacitors and reactors are considered to be installed in the distribution system at the same time.The objective function is the cost minimization of compensation and real power loss with transformers and lines during the planning period.Nodal power factor limits and reactor capacity constraints are new constraints.Then,power factor sensitivity with respect to reactive power is derived.An improved genetic algorithm by power factor sensitivity is used to solve the model.The optimal locations and sizes of reactors and capacitors can avoid reactive power reversal and power factor exceeding the limit.Finally,the effectiveness of the model and algorithm is proven by a typical high-voltage distribution network.

Research of Electric Cable Path Planning Based on Heuristic Optimization Algorithm in Mixed-Land Scenario

In order to improve the reliability of power supply,the sophisticated design of the structure of electric cable network has become an important issue for modern urban distribution networks.In this paper,an electric cable path planning model based on heuristic optimization algorithm considering mixed-land scenario is proposed.Firstly,based on different land samples,the kernel density estimation(KDE)and the analytic hierarchy process(AHP)are used to estimate the construction cost of each unit grid,in order to construct the objective function of comprehensive investment for electric cable loop network.Then,the ant colony optimization(ACO)was improved in pheromone concentration,factor increment and search direction to accelerate the solving speed,and the cable path planning result with minimum construction cost is obtained.Finally,the feeder’s tie line of the cable loop network is planned by the genetic algorithm(GA)to achieve the minimum operating cost.In the case analysis,compared with the traditional method,not only the subjective factors in the process of investment estimation can be avoided,but also the speed of model solving and the quality of the optimal solution are improved.

Shaking table test and numerical analysis of offshore wind turbine tower systems controlled by TLCD

A wind turbine system equipped with a tuned liquid column damper(TLCD) is comprehensively studied via shaking table tests using a 1/13-scaled model. The effects of wind and wave actions are considered by inputting responseequivalent accelerations on the shaking table. The test results show that the control effect of the TLCD system is significant in reducing the responses under both wind-wave equivalent loads and ground motions, but obviously varies for different inputs. Further, a blade-hub-tower integrated numerical model for the wind turbine system is established. The model is capable of considering the rotational effect of blades by combining Kane's equation with the finite element method. The responses of the wind tower equipped with TLCD devices are numerically obtained and compared to the test results, showing that under both controlled and uncontrolled conditions with and without blades' rotation, the corresponding responses exhibit good agreement. This demonstrates that the proposed numerical model performs well in capturing the wind-wave coupled response of the offshore wind turbine systems under control. Both numerical and experimental results show that the TLCD system can significantly reduce the structural response and thus improve the safety and serviceability of the offshore wind turbine tower systems. Additional issues that require further study are discussed.

Calculation of the Two High Voltage Transmission Line Conductors’ Minimum Distance

In the design of high voltage transmission lines inevitably needed to change the arrangement of wires, and the distance between the wires directly affected by changing the arrangement of the wires. The distance between the wires is difficult to judge by experiences. Therefore, it is urgently to develop a way to accurately calculating the minimum distance between the wires when changing the arrangement between the two wires, and determine the minimum distance can meet the requirements of standards and regulations or not. Through the thinking, based on the balance equation and the space curve wire calculus method, a more accurate method of calculating the two wires in a variety of conditions the minimum spacing was derivated, and the sensitivity of the minimum distance was analysized based on the method.

Maximum entropy based probabilistic load flow calculation for power system integrated with wind power generation

Distributed generation including wind turbine(WT) and photovoltaic panel increases very fast in recent years around the world, challenging the conventional way of probabilistic load flow(PLF) calculation. Reliable and efficient PLF method is required to take this chage into account.This paper studies the maximum entropy probabilistic density function reconstruction method based on cumulant arithmetic of linearized load flow formulation,and then develops a maximum entropy based PLF(MEPLF) calculation algorithm for power system integrated with wind power generation(WPG). Compared with traditional Gram–Charlier expansion based PLF(GC-PLF)calculation method, the proposed ME-PLF calculation algorithm can obtain more reliable and accurate probabilistic density functions(PDFs) of bus voltages and branch flows in various WT parameter scenarios. It can solve thelimitation of GC-PLF calculation method that mistakenly gains negative values in tail regions of PDFs. Linear dependence between active and reactive power injections of WPG can also be effectively considered by the modified cumulant calculation framework. Accuracy and efficiency of the proposed approach are validated with some test systems. Uncertainties yielded by the wind speed variations, WT locations, power factor fluctuations are considered.

Optimal allocation of hybrid energy storage for microgrids based on multi-attribute utility theory

To satisfy the requirements of high energy density,high power density,quick response and long lifespan for energy storage systems(ESSs),hybrid energy storage systems(HESSs)have been investigated for their complementary characteristics of‘high energy density components’and‘high power density components’.To optimize HESS combinations,related indices such as annual cost,fluctuation smoothing ability as well as safety and environmental impact have to be evaluated.The multiattribute utility method investigated in this paper is aimed to draw an overall conclusion for HESS allocation optimization in microgrid.Building on multi-attribute utility theory,this method has significant advantages in solving the incommensurability and contradiction among multiple attributes.Instead of determining the weights of various attributes subjectively,when adopting the multi-attribute utility method,the characteristics of attributes and the relation among them can be investigated objectively.Also,the proper utility function and merging rules are identified to achieve the aggregate utility which can reflect comprehensive qualities of HESSs.