Nasser Al-Emadi

A New Low Cost Linear Resolver Converter

A new low cost converter topology is proposed for sinusoidal position encoders. The converter enables determination of the angle from the sine and cosine signals of the encoder. When used with resolvers, the implementation of the present scheme takes advantage of the available excitation signal used to operate the device. This trigonometric reference signal is optimally used to generate an analogue signal equivalent to a digital look-up table (LUT). This enables determination of the mechanical angle without using LUT, A/D, and D/A converters. The scheme is optimized in order to achieve highest possible precision. Beside simplicity of its implementation, the proposed converter offers the advantage of robustness to amplitude fluctuation of the transducer excitation signal. The converter was implemented using ordinary low-cost analog components. The theory of operation, computer simulation, and experimental results are given.

Preventive and corrective open access system dispatch based on the voltage stability security assessment and diagnosis

Abstract The capabilities of the voltage stability security assessment (VSSAD) to assess proximity to and ranking voltage instability by (a) performing a contingency selection of each model determined subsystem and (b) diagnosing where, why, when and what can be done to cure voltage instability for each equipment outage and transaction combination is thoroughly documented in IEEE Trans. Power Syst. 13 (1998) 1423; Division of Engineering Research Technical Report December 1998, Santorini, Greece. This paper reviews these capabilities and how they can be used to implement a contingency selection module and security constrained optimization module for the open access system dispatch (OASYDIS) being proposed as part of the proposed transmission dispatch and congestion management (IEEE Trans. Power Syst. 13 (1998) 1466) in an ISO. The open access system dispatch can be implemented as either a preventive control as given in IEEE Trans. Power Syst. 13 (1998) 1466 or as a corrective control as proposed in this paper. The VSSAD based contingency selection can provide the security constraints for either a preventive or corrective control implementation of OASYDIS. The advantages of corrective control are discussed and the changes in the proposed open access system dispatch (IEEE Trans. Power Syst. 13 (1998) 1466) required to implement a corrective control are discussed.

Matlab/Simulink implementation & simulation of islanding detection using passive methods

The extensive use of Distributed Generators in Electrical and power systems made it a must to explore its functionality and the issues related to their connection to the grid. One of the main issues is unintentional islanding, which has been considered and studied for many years since it has serious consequences on electric systems and line workers safety. Therefore, islanding detection methods is a motivating topic to be discussed by many scientists and engineers. Islanding detection methods can be divided into two main categories, remote methods and local methods; the later method is classified into passive techniques and active techniques. This paper represents two methods of the passive islanding techniques and a simple comparison between both of them. The selected two methods are the over/under voltage and over/under frequency detection method and the wavelet based method. These two were implemented and simulated using Matlab/Simulink toolboxes. The simulation results proved that the two studied methods have a good performance for parallel RLC loads having quality factor of 2.5. The simulated passive techniques have no negative impact on the power quality.

A resolver converter based upon a novel open-loop technique

The paper presents a novel technique for the determination of the angle from slowly-varying quadrature co- sinusoidal signals produced, for example, by position sensors. In the presented scheme applied to a resolver, the separately generated constant-frequency sine wave used for exciting the resolver together with an additional cosine wave are used as reference against which the amplitudes of the angle-dependent demodulated resolver sine and cosine signals are compared. At the instant equality between respective amplitudes of the signals are detected, two sample and hold circuits sample a voltage proportional to the angle of the shaft of the resolver from a triangular waveform generated from the reference signals. In theory, the sample and hold devices produce identical output voltages proportional to the unknown angle of the transducer. In order to improve the precision of the proposed converter, the two sample and hold circuits outputs are fed into a multiplexer to produce a single output that takes full advantage of the accurate comparison outside the peak regions of the signals. With this method, the validated output is obtained from the accurate comparisons involving the alternating pseudo-linear segments of the trigonometric signals. Another important feature of this converter is its robustness to amplitude fluctuations in the trigonometric reference signals which are used for the excitation of the resolver. A converter based on this technique has been successfully implemented using basic electronic components. Theory of operation, computer simulation and experimental results are given.

Frequency and voltage partitioning in presence of renewable energy resources for power system (example: North Chile power network)

This paper investigates techniques for frequency and voltage partitioning of power network based on the graph-theory. These methods divide the power system into distinguished regions to avoid the spread of disturbances and to minimize the interaction between these regions for frequency and voltage control of power system. In case of required active and reactive power for improving the performance of the power system, control can be performed regionally instead of a centralized controller. In this paper, renewable energy sources are connected to the power network to verify the effect of these sources on the power systems partitioning and performance. The number of regions is found based on the frequency sensitivity for frequency partitioning and bus voltage for voltage partitioning to disturbances being applied to loads in each region. The methodology is applied to the north part of Chile power network. The results show the performance and ability of graph frequency and voltage partitioning algorithm to divide large scale power systems to smaller regions for applying decentralized controllers.

An open-loop technique for angle determination from position encoders

The paper presents a novel technique for the determination of the angle from low-frequency quadrature cosinusoidal signals produced, for example, by position sensors. In the presented scheme applied to a resolver, the separately generated constant-frequency sine wave used for exciting the resolver together with an additional cosine wave are used as reference against which the amplitudes of the angle-dependent demodulated resolver sine and cosine signals are compared. At the instant equality between amplitudes of respective signals are detected, a sample and hold circuit samples a voltage proportional to the angle of the shaft of the resolver from a triangular waveform generated from the reference signals. This is a feed-forward method, which is an analog equivalent to digital look up table techniques. In order to improve the precision of the proposed converter, a new technique is used to take full advantage of the alternating pseudo-linear segments of the trigonometric signals. With this method, the sampling relies only on the accurate comparison outside the peak regions of the signals. A converter based on this technique has been successfully implemented using basic electronic components. Theory of operation, computer simulation and experimental results are given.