Tek Tjing Lie

A Statistical Approach to the Design of a Dispatchable Wind Power-Battery Energy Storage System

A scheme that allows the dispatch of steady and controllable level of power from a wind power generating station is proposed in this paper. The scheme utilizes two battery energy storage systems (BESSs) in which the generated wind power is used to charge one BESS, while the second BESS is used to discharge constant power into grid. The role of the two BESS interchanges when the discharging BESS reaches specified operating limit. With this scheme in mind and based on given wind speed statistics, charging characteristics of the BESS are studied, and a method to determine the expected charging time of the BESS to reach stipulated battery state of charge is developed. The expected BESS charging time, in turn, dictates the constant power level that can be dispatched to the grid through the discharging BESS. The corresponding discharge time is also determined using the developed method, the accuracy of which is validated experimentally. The proposed design procedure is then used to determine the minimum BESS capacity based on the expected wind power. Statistical likelihood of dispatchable power delivery achievable from the scheme is also obtained.

Opportunities for Software-Defined Networking in Smart Grid

The large-scale, heterogeneous, and distributed nature of the Smart Grid poses many challenges to be overcome from communication networking to autonomous control and management. The underlying infrastructure of Smart Grid must be efficient and reliable in transmitting large amounts of real-time data, scalable and flexible in aggregating resources, and secured and convenient in providing management interfaces to upper layer application systems. Meanwhile, the recent rapidly developing technology of Software Defined Networking (SDN) is perceived to have tremendous potential for utilization by the underlying infrastructure. By abstracting control functionalities from underlying packet forwarding hardware to an external software controller, SDN offers a high degree of flexibility for implementing novel networking solutions to improve performances of distributed systems in large, complex network environments such as Smart Grid. In this paper, three potential use cases are presented to examine the opportunities for SDN technology in Smart Grid.

Configure Methodology of Onboard Supercapacitor Array for Recycling Regenerative Braking Energy of URT Vehicles

Onboard energy storage system (ESS) is an important energy-saving technology in urban rail transit. The key issue of the ESS is the array configuration. In this paper, a new array configuration methodology is developed. First, the limitations of the capacity-constrained configuration method, which is mainly adopted for configuring the onboard supercapacitor array (OSA), are investigated. Second, a mathematical model of the OSA is developed taking into account power and capacity constraints so that the absorbed braking energy can be recovered. Finally, a powerand capacity-constrained configuration methodology (P&C-Method) is proposed. Digital simulation studies are conducted, and the results show that the OSA with the proposed P&C-Method can realize the effective energy recovery of the whole absorbed braking energy and have a high energy-saving effect/weight ratio.

Computation of the Thermal Effects of Short Circuit Currents on HTS Transformer Windings

The active development of high temperature superconductor (HTS) materials has led to extensive research and development studies of superconducting transformers worldwide. Considerable benefits have been accomplished with the introduction of the HTS transformer such as reduced power loss, size, and transformer weight. However, recent advancement in the design technology has focused on the HTS transformers ability to also perform as a fault current limiter (FCL). This paper presents the computation of the thermal effects of short circuit currents on a non-FCL HTS transformer and demonstrates how it will behave with an HTS-FCL winding conductor.

Determination of a dispatch strategy to maximize income for a wind turbine-BESS power station

A dispatch strategy is proposed for the purpose of maximizing the income for a wind turbine - dual battery energy storage power station. The strategy takes into consideration the complex relationship between the efficiency of the battery and the BESS discharge level while meeting the prevailing power market rules. The technique requires an accurate forecast in both the variable wind power and electricity tariff. Solution to the optimization problem is based on an iterative computational procedure. A case study is included to demonstrate the main findings of this investigation.

The Effects of Short-Circuit and Inrush Currents on HTS Transformer Windings

Rapid changes and developments are being witnessed in the transformer design technologies. The phenomenal growth of power systems has put tremendous responsibilities on the industry to supply reliable and cost-effective transformers. The advent of high-temperature superconductor (HTS) materials has increased interest in research and development of superconducting transformers with major projects being carried out worldwide. The major challenges in the design and development of HTS transformers are the modeling of short-circuit and inrush currents the transformer can withstand. Even though HTS technology is claimed to be more efficient, reliable, and eco-friendly, use of HTS transformers must be appropriately verified through the proper modeling of power system network.

Wind speed forecasting using hybrid ANN-Kalman Filter techniques

Wind intermittency, independent nature of direction, speed was the best-known challenge and major barrier against wind power penetration. Precise forecasting of wind speed is vital to the effective harvesting of wind power. The problems posed in the wind speed prediction include reduction in time delay, improvement in speed for short time, error reduction, model improvement for effective conversion of wind energy. However there is a lot of research being done in this field in which individual as well as hybrid techniques are being worked upon. The objective of this paper is on error reduction and improvement of model by hybridizing two techniques. One is the Artificial Neural Networks (ANN) along with a statistical method of Ensemble Kalman Filter (EnKF) technique. These methods are used for short term predictions of wind speed. This result is tested practically on MATLAB in this paper. By help of observations, the EnKF will correct the output of ANN to find the best estimate of wind speed. Results in MATLAB show that combination of ANN with EnKF acts as an output correction scheme.

Three-phase modeling of HTS transformer in distribution networks

Transformers utilizing high temperature superconductors (HTS) are considered as a timely invention. The number of power transformers age more than 30 years old and nearing retirement is increasing. If this window of opportunity is not grabbed, there would be great reluctance to replace recently installed highly priced capital asset. Major projects of developing HTS transformers are well making progress in the United States, Europe, Japan, Korea and China which indicate the interest. The efforts must have been appropriately verified through the economic interest of the discounted losses. Consequently, it is very important to develop an understanding of the fundamental HTS transformer design issues that can provide guidance for developing practical devices of interest to the electric utility industry. The parameters of HTS transformer need to be validated before any effort is to carry out to model the behaviour of a distribution network under a range of conditions. The predicted performance and reliability of HTS transformers can then be verified through the network modelling and analysis calculation. The ultimate purpose is to furnish electric utilities precise information as to which HTS transformers work under various applications with greater technical efficiency and proven reliability.

Dynamic study of a battery change-over scheme of a windfarm containing dual BESS

The wind farm-dual-battery energy storage systems (BESS) described in [1] is studied in greater detail for those instances when the battery banks change-over. The primary design objective of the wind farm-BESS scheme is to realize the dispatchability of wind generation. The scheme requires two BESS modules to inter-change between charging-discharging modes. A new power flows control strategy is designed to cater for the battery switching-over operation while practical constraints on the charging-discharging of the BESS are considered. A dynamic study is included to illustrate the strategy.

Performance analysis of HTS transformer with fault current limiting properties on short circuit current

The advent of High Temperature Superconductor (HTS) materials has increased interest in research and development of superconducting transformers with major projects being carried out worldwide. Several benefits were accomplished with the introduction such as lower power loss, smaller size and lighter weight transformer. However, recent development on HTS transformer has focused on its ability to also function as Fault Current Limiter (FCL). This paper will show the performance of a non-FCL HTS transformer on short circuit current and predict how it will behave with HTS-FCL transformer winding conductor architectures.