Nadipuram R. Prasad

A study of islanding in utility-connected residential photovoltaic systems

Islanding is the continued operation of a group of utility-connected photovoltaic systems even after loss of the utility source. Such operation can be hazardous to both utility personnel as well as to components in the system. Models and methods for the analysis of this phenomenon are presented in this paper. The methods are used in a companion paper to explore the possibility of islanding in practical systems. Although all such systems have a natural propensity to island, it is shown that the controls used in many commercially available units make islanding a rather unlikely phenomenon.

Fuzzy-logic-based speed control of a shunt DC motor

The fundamental equations governing the operation of a DC motor are straightforward and are well presented in most undergraduate curricula, usually in a required energy conversion or electrical machinery class at the junior level. The physical implications of the equations regarding device behavior, and the need for speed control, are easily understood. Furthermore, students can readily develop a mental picture of the physical motor and its response. Speed control of a DC motor represents an ideal application for introducing the concepts of fuzzy logic. Once the fundamentals of fuzzy logic have been presented to the students, their application to the speed control problem can be easily demonstrated. The paper shows how a commercially available fuzzy logic development kit can be applied to the theoretical development of a fuzzy controller for motor speed, which represents a very practical class of engineering problems.

Effects of pulsed-power loads upon an electric power grid

Certain proposed particle-accelerator and laser experiments, and other devices related to fusion research, require multi-megawatt, repetitive power pulses, often at low (subsynchronous) frequency. While some power-delivery technologies call for a certain degree of buffering of the utility demand using capacitive, inductive, or inertial energy storage, considerations have also been made for serving such loads directly from the line. In either case, such pulsed loads represent non-traditional applications from the utilitys perspective which, in certain cases, can have significant design and operational implications. This paper outlines an approach to the analysis of the effects of such loads upon the electric power grid using existing analysis techniques. The impacts studied include busvoltage flicker, transient and dynamic stability, and torsional excitation. The impact of a particular pulsed load is examined and illustrated for the power network serving the Los Alamos National Laboratory. 19 refs., 13 figs.

Eliminated Common-Mode Voltage Pulsewidth Modulation to Reduce Output Current Ripple for Multilevel Inverters

The paper presents an analysis on the output current ripple in zero common-mode voltage (ZCMV) PWM control of multilevel inverters. The modulation strategy for common-mode voltage (CMV) elimination in multilevel inverters is based on the “three zero common-mode vectors” principle. The space vector diagram, which consists of vectors of ZCMV, is fully explored by properly depicting the base voltage vectors and their corresponding active switching vectors. The switching patterns are limited to those of three switching states each of which is symmetrically distributed. Based on the PWM process simplified to that of a two-level inverter with three allowable switching states and the degree of freedom existing in the switching states arrangement, a novel carrier-based pulsewidth-modulated (PWM) method with optimized output current ripple is proposed. Compared to the existing PWM methods which utilize the same kind of switching patterns, the proposed PWM method has reduced considerably the rms current ripple and total harmonic distortion (THD) of the output current in a wide region of the modulation index. The effectiveness of the proposed method is validated by both simulation and experimental results.

Approach to combining case based reasoning with rule based reasoning for lung disease diagnosis

In recent years, we have developed an expert system for the diagnosis of lung diseases using cased-based reasoning and other rule-based systems using fuzzy logic. Case-based reasoning is the process of using solutions to previously encountered problems as a basis for reasoning solution to new problems. The knowledge base of the Case-Based Reasoning System for Diagnosis of Lung Diseases is a case base of patient records consisting of documented experience. On the other hand, the knowledge base of the Expert System for Lung Diseases is a set of IF-THEN rules based on the experience of medical doctors. In fact, these two systems make diagnoses of lung diseases based on two different knowledge bases. One is a case base and other is a rule base. Our design combines the diagnoses of these two methods in order to obtain improved accuracy in lung disease diagnosis. In this paper, we offer an approach to combining case-based reasoning and rule-based reasoning for lung disease diagnosis.

Identification of trash types in ginned cotton using neuro fuzzy techniques

Discusses the use of soft computing techniques such as neural networks and fuzzy logic based approaches in the identification of various types of trash (non-lint material/foreign matter) in ginned cotton. Lint is the cotton fiber; non-lint or foreign matter is everything other than lint. The effectiveness of a hybrid neuro-fuzzy structure, namely the adaptive-network-based fuzzy inference system to classify trash types is compared to other techniques. Shape descriptors like shape factor, extent, and solidity measures are used as features to distinguish trash types.

Hierarchical fuzzy control

In this paper, a simplified method for developing Takagi-Sugeno-Kang (TSK) style fuzzy controllers is described. The method takes advantage of developers knowledge and understanding of the system being implemented. System attributes such as variable and nonlinearity independence are utilized to significantly reduce the required rule-base size when describing the system, without compromising robustness and performance. An example of a tracking system is used to convey the process of implementing a hierarchical fuzzy controller.

State estimation with aid of fuzzy logic

The paper presents an approach to power system state estimation based on the application of fuzzy logic. Significant improvements in state estimates are achieved (relative to the weighted least squares algorithm) by using a hybrid estimator incorporating fuzzy logic concepts. The design of the fuzzy estimator is described. The approach is illustrated for two sample systems: a 6-bus and a 30-bus system.

A fuzzy-logic-supported weighted least squares state estimation

Abstract This paper presents a new approach to power system state estimation based on the application of fuzzy logic. Significant improvements in state estimates are achieved (relative to the weighted least squares algorithm) by using a hybrid estimator incorporating fuzzy-logic concepts. The design of the fuzzy estimator is described. The approach is illustrated for two sample systems: a 6-bus network and the 30-bus IEEE test system. Numerical and graphical results are presented to illustrate the superiority of the new method.

Dynamic wavefront sensor system using spatial light modulators

Liquid crystal televisions (LCTVs) have become very popular spatial light modulators. Their polarization and phase modulation capabilities allow them to be used as inexpensive spatial light modulators in a wide variety of applications. The design of a dynamic Hermann wavefront sensor system is described. A LCTV is used as an aberration generator in an optical system. A LCTV is also used as a Harmann wavefront sensor to measure the aberrations. Experimental results characterizing the LCTVs performance as an aberration generator and Harmann wavefront sensor are presented.