Sri R. Kolla

Robust stability bounds on time-varying perturbations for state-space models of linear discrete-time systems

The stability robustness of linear discrete-time systems in the time domain is addressed using the Lyapunov approach. Bounds on linear time-varying perturbations that maintain the stability of an asymptotically stable linear time-invariant discrete-time nominal system are obtained for both structured and unstructured independent perturbations. Bounds are also derived assuming that various elements of the system matrix are perturbed dependently. The result for the structured perturbation case is extended to the stability analysis of interval matrices.

Identifying three-phase induction motor faults using artificial neural networks

This paper presents an artificial neural network (ANN) based technique to identify faults in a three-phase induction motor. The main types of faults considered are overload, single phasing, unbalanced supply voltage, locked rotor, ground fault, over-voltage and under-voltage. Three-phase currents and voltages from the induction motor are used in the proposed approach. A feedforward layered neural network structure is used. The network is trained using the backpropagation algorithm. The trained network is tested with simulated fault current and voltage data. Fault detection is attempted in the no fault to fault transition period. Off-line testing results on a 3 HP induction motor model show that the proposed ANN based method is effective in identifying various types of faults.

Fieldbus networks for control system implementations

Industrial digital communication networks called fieldbuses are becoming more popular in control system implementations for use in automated manufacturing systems. This paper presents an overview of the current state of these fieldbus networks. It first gives various advantages of using fieldbus networks over point-to-point connections for control system implementations. Then, the generic ISO/OSI seven-layer communication protocol model is discussed and the deviations from this model for various fieldbus networks are identified. Hardware and software aspects of fieldbus networks are reviewed. Finally, some of the issues in selecting a fieldbus network for a given application are examined.

Improved stability robustness bounds using state transformation for linear discrete systems

Abstract Sufficient-condition bounds on the linear time-varying perturbations for robust stability of an asymptotically stable linear time-invariant discrete-time system have been reported recently. The development involves both Schwartz and triangular inequalities, and tends to give conservative results. This paper uses state transformation to obtain improvement in these bounds. Both unstructured and structured perturbation bounds are shown to improve using transformations. The proposed analysis is applied to a fourth-order macroeconomic system model.

Real-time monitoring of critical nodes with minimal number of Phasor Measurement Units

This paper presents a method for placement of Phasor Measurement Units, ensuring the monitoring of vulnerable buses which are obtained based on transient stability analysis of the overall system. Real-time monitoring of phase angles across different nodes, which indicates the proximity to instability, the very purpose will be well defined if the PMUs are placed at buses which are more vulnerable. The issue is to identify the key buses where the PMUs should be placed when the transient stability prediction is taken into account considering various disturbances. Integer Linear Programming technique with equality and inequality constraints is used to find out the optimal placement set with key buses identified from transient stability analysis. Results on IEEE-14 bus system are presented to illustrate the proposed approach.

Improved robust stability bounds for discrete-time linear regulators with computational delays

Abstract Recently obtained stability robustness bounds on linear time-varying perturbations of an asymptotically stable linear time-invariant discrete-time system are applied to linear regulators with computational delays. The bounds were developed using Lyapunov theory and singular value decomposition for unstructured and structured time-varying perturbations. The new structured perturbation bound may provide improved results for the elemental perturbations over a bound based on the unstructured perturbation bound of Ishihara (1988, Automatica, 24, 696–700), as indicated both by an example and by sufficient conditions.

Evaluation of component-based reconfigurable machine controllers

The lack of interoperability and integration standards is severely hindering manufacturing productivity. To address this problem, a general motion control (GMC) testbed has been developed at National Institute of Standards and Technology (NIST) with one of its goals to validate the open modular architecture controller (OMAC) interface specification for reconfigurable, plug-and-play open-architecture controllers. The GMC validation testbed was built using Microsoft component object model (COM) components. This paper reviews software programming issues and the use of Microsoft COM in the development of machine control components. Strategies and tests of COM programming for a controller are discussed.

Application of block pulse functions for digital protection of power transformers

The author describes an application of block pulse functions for digital protection of power transformers. Digital relay algorithms are developed to extract fundamental and second-harmonic components. These components are then used for harmonic restraint differential protection of transformers. In comparison with the algorithms based on the Walsh and Haar functions, the proposed method is computationally simple and can be used with any sampling frequency. It is concluded that offline testing of the method with simulated inrush and internal fault current data clearly indicate that the method can provide fast and reliable trip decision. The method is suitable for microprocessor-based protective relays. >

Improved stability robustness bounds for digital control systems in state-space models

This paper presents stability robustness bounds for linear discrete-time systems with time-invariant perturbations. These bounds extend the previous investigations for independent perturbations to dependent perturbations and provide improved results. It is shown that the dependent perturbation bound includes an independent perturbation bound previously reported as a special case. These results are illustrated with simple examples.

Application of block pulse functions in a polyphase digital distance relay

This paper presents a digital distance relay scheme for power transmission line protection. The scheme uses a single criterion to determine the fault distance during the ten types of shunt faults on a three-phase transmission line. The criterion is derived using a modal transformation. The scheme uses a recently developed algorithm based on block pulse functions to compute fundamental frequency voltage and current phasors of fault signals. The scheme is tested using simulated voltage and current signals obtained from the electromagnetic transient program (EMTP). These simulations are performed on a 230 kV transmission line of a six bus power system model.