Wei Zhan

Development of a Low-Cost Self-Diagnostic Module for Oil-Immerse Forced-Air Cooling Transformers

Fault detection, fault prognosis, and life expectancy estimation of transformers are important issues in improving the reliability of smart grids. Regular maintenance checks can detect the transformers faulty conditions; however, such checks can only be performed limited times annually due to high cost and disruption of service. Therefore, faults that occur between such checks take a long time to be detected. This paper proposes a simple online monitoring algorithm that uses a minimum set of sensor feedback to estimate oil-immersed forced-air cooling transformers life expectancy parameters. Abrupt changes or sufficient deviations of these estimations from their nominal values can be used as an indicator of transformer fault. The algorithm can also estimate the transformer-life expectancy during normal operation. A transformer-monitoring prototype has been developed based on the proposed algorithm. The transformer-monitoring prototype that uses wireless communication capability to transmit transformer life expectancy parameters to the substation has been tested, verified with lab experiments, and deployed to a utility substation.

An inequality governing nonlinear H ∞ control

Abstract This note gives necessary and sufficient conditions for solving a reasonable version of the nonlinear H ∞ control problem. The most objectionable hypothesis is elegant and holds in the linear case, but every possibly may not be forced for nonlinear systems. What we discover in distinction to Isidori and Astolfi (1992) and Ball et al. (1993) is that the key formula is not a (nonlinear) Riccati partial differential inequality, but a much more complicated inequality mixing partial derivatives and an approximation theoretic construction called the best approximation operator. This Chebeshev-Riccati inequality when specialized to the linear case gives the famous solution to the H ∞ control problem found in Doyle et al. (1989). While complicated the Chebeshev-Riccati inequality is (modulo a considerable number of hypotheses behind it) a solution to the nonlinear H ∞ control problem. It should serve as a rational basis for discovering new formulas and compromises. We follow the conventions of Ball et al. (1993) and this note adds directly to that paper.

Piecewise Riccati equations and the bounded real lemma

This article concerns piecewise linear systems and determining if they meet given H/sup /spl infin// performance specifications. Such problems occur in control of linear systems with saturation nonlinearities. While one could imagine many mathematically natural piecewise linear systems problems we took care to extract one which does correspond to control of saturated plants. We think many such problems will fall into the category treated here. After a serious compromise (which makes our test for meeting specifications conservative), we arrive at a type of piecewise Riccati equation. Even these look formidable, however we begin a study of them.<<ETX>>

Analysis of Impact of Various Factors on Downwind Deposition Using a Simulation Method

The drift of aerially applied crop protection and production materials is studied using a novel simulation-based design of experiments approach. Many factors that can potentially contribute to downwind deposition from aerial spray application are considered. This new approach can provide valuable information about the significant level of the impact from all factors and interactions among them that affect drift using simulation software such as AGDISP. The application efficiency, the total downwind drift, the cumulative downwind deposition between 30.48 m (100 ft) and 45.72 m (150 ft), and the deposition at 30.48 m (100 ft), 76.2 m (250 ft), and 152.4 m (500 ft) are established as the performance metrics. The most significant factors will be identified using statistical analysis based on simulation results, and suggestions for improvement will be made. Through preliminary study, the new simulation-based method has shown the potential for statistic analysis without conducting time-consuming field experiments. The new method can be used to search for the optimal spray conditions, which could be used to generate guidelines for applicators to achieve an optimal spray result. The effective use of simulation tool through the identification of significant factors can greatly simplify the field study.

Optimal selection of wireless channels for real-time communication in ambulances

The design and implementation of ambulances that exchange high quality video, vital signs, voice and text communications, and patient information in real-time with the emergency room are becoming a reality. For instance, the Disaster Relief and Emergency Medical Service (DREAMStrade) project has developed such ambulances. Through wireless Internet access, the ambulances take advantage of the widespread cellular coverage in rural and urban areas to transfer audio, video and vital signs. In this paper, our goal is to improve the intelligence of the channel selection mechanism of the ambulance based on metrics such as data transfer efficiency and reliability. Using a simple optimization algorithm, we propose a strategy to assign the next designated channel for the high priority data.

A Design of Experiment (DOE) Analysis of the Performance of Uplink Real-Time Traffic over a 3G Network

The bandwidth and reliability of the reverse link (or uplink) as the performance metrics of real-time traffic are studied in this paper. A two-level full factorial design of experiment (DOE) was conducted to identify the impact on the bandwidth and reliability of four factors: packet size, data streaming rate, time of the day, and buffer size in a real network environment. Two extreme cases for each factor were tested and statistical analysis is performed to characterize how different factors and their interactions may affect the bandwidth and reliability. The importance of this study is illustrated in the optimal channel selection mechanism where appropriate packet size, data streaming rate and buffer size can be chosen to achieve the best result.

A regression algorithm for transformer fault detection

A transformers failure can lead to disruption in power, decrease in system reliability and monetary loss to the utility and distribution companies. Fault detection of transformers is a critical step for improving the reliability of distribution systems. Regular maintenance checks can detect most of faulty conditions, but due to high cost and difficulty, the maintenance checked can only be performed annually. This paper proposes a simple on-line monitoring algorithm that uses a minimum set of sensor information, including ambient temperature, hot spot temperature, and load, to estimate several system parameters such as oil and thermal properties of the transformer and detect abnormal behavior. Fault can be detected when these parameter estimations experience sudden changes or the estimated values have sufficient deviation from their nominal values.

Reducing simulation time using design of experiments

Purpose – The purpose of this paper is to demonstrate the effectiveness of Six Sigma as an innovative tool in software design optimization. The problem of reducing simulation time for characterizing a type of DC motor is studied in this paper. The case study illustrates how Six Sigma tools such as the design of experiments (DOE) method can be used to improve a simulation process.Design/methodology/approach – A first‐principle model for the motor is used for simulation in MATLAB®. Each parameter in the model is assumed to have a known distribution. Using the random number generator in MATLAB®, Monte Carlo analysis is conducted. To reduce simulation time, several factors in the simulation process are identified. A two‐level full factorial DOE matrix is constructed. The Monte Carlo analysis is carried out for each of the parameter set in the DOE matrix. Based on the simulation results and the DOE analysis, the Simulink model is identified as the main contributor to the computational time of the simulation. S...

Modeling, Simulation, and Analysis for Battery Electric Vehicles

Steady state and dynamic vehicle models are derived for analyses of requirements on motors and batteries for battery electric vehicles. Vehicle level performance requirements such as driving range, maximum cruise speed, maximum gradeability, and maximum acceleration are used to analyze the requirements on motors and batteries including motor power and torque, battery weight and specific energy. MATLAB simulation tools are developed to allow validation of these vehicle level performance requirements for a given set of motor/battery.

Statistical Analysis of Broadband Wireless Links in Rural Areas

Third-generation (3G) cellular systems are often considered as a promising strategy for high-speed internet deployment in rural areas. However, bandwidth in 3G systems is a limited resource and can be quite different from the advertised bandwidth. In addition, in wireless applications such as voice over IP, video-conference, remote monitoring and telemetry (e.g., for healthcare applications) the Quality of Service (QoS) is critical. It is therefore important to understand how different factors affect the QoS requirements of real-time applications. Focusing on the reverse link (or uplink), we performed an assessment of the bandwidth and packet loss rate in a real network environment, using test data collected with two wireless data cards from different providers, in both rural and urban locations. The main contribution of this paper is the presentation of a formal statistical method – a Design of Experiments (DOE) analysis - that can be used to analyze the interactions between different variables, such as packet size, location, buffer size, and wireless provider. With a better understanding of the impact of such factors and their interactions, the end-user may be able to make the best selection of certain controllable parameters, in an effort to improve the QoS of the 3G connection. This is especially important for users located in rural areas, where cellular coverage is limited.