Electrical Engineering

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The paper is concerned with the design of a hybrid controller structure, consisting of the adaptive control law and a neural-network-based learning scheme for adaptation of time-varying controller parameters. The target error vector for weight adaptation of the neural networks is derived using the Lyapunov-function approach. The global stability of the closed-loop feedback system is guaranteed, provided the structure of the robot-manipulator dynamics model is exact. Generalisation of the controller over the desired trajectory space has been established using an online weight-learning scheme. Model learning, using a priori knowledge of a robot arm model, has been shown to improve tracking accuracy. The proposed control scheme has been implemented using both MLN and RBF networks. Faster convergence, better generalisation and superior tracking accuracy have been achieved in the case of the RBF network. © IEE, 1996.

World University root node

(SoE) School of Engineering

IEE Proceedings: Control Theory and Applications

Neuro-adaptive hybrid controller for robot-manipulator tracking control

A robust hybrid control method that integrates a neural controller, and a H∞ controller is proposed. The neural controller is designed for feedback linearization and the H∞ controller is used to minimize the effect of parameter uncertainties of the model on the tracking performance. Simulations are provided to show that the disturbances generated from the model error will be quickly compensated and hence more robust performance can be achieved.

IEEE International Conference on Neural Networks - Conference Proceedings

Robust hybrid controller for robotic manipulators using neural and H∞ techniques

This paper is concerned with the design of a neuroadaptive trajectory tracking controller. The paper presents a new control scheme based on inversion of a feedforward neural model of a robot arm. The proposed control scheme requires two modules. The first module consists of an appropriate feedforward neural model of forward dynamics of the robot arm that continuously accounts for the changes in the robot dynamics. The second module implements an efficient network inversion algorithm that computes the control action by inverting the neural model. In this paper, a new extended Kalman filter (EKF) based network inversion scheme is proposed. The scheme is evaluated through comparison with two other schemes of network inversion: gradient search in input space and Lyapunov function approach. Using these three inversion schemes the proposed controller was implemented for trajectory tracking control of a two-link manipulator. Simulation results in all cases confirm the efficacy of control input prediction using network inversion. Comparison of the inversion algorithms in terms of tracking accuracy showed the superior performance of the EKF based inversion scheme over others. © 1996 IEEE.

Fulltext

IEEE Transactions on Neural Networks

On adaptive trajectory tracking of a robot manipulator using inversion of its neural emulator

A query based learning algorithm is proposed in this paper to obtain a valid neural emulator of the robot manipulator using radial basis function networks. This algorithm is centred around the concept of network inversion for which we have proposed an extended Kalman filtering (EKF) based algorithm. Initially the training data set is generated by tracking various random trajectories in robot work space. During this process, control input (or joint actuating torque) vector is computed using a fixed PD control scheme with added dither signal. The RBF network thus learned is tested for its validity using the inversion based recall process. In case the neural network is partially trained, additional input/output data pairs are generated. The data so generated are used to retrain the RBFN model of the robot manipulator. Experiments showed significant improvement in the neural model after retraining. © 1996 Taylor & Francis Group, LLC.

IETE Journal of Research

A Query Based Learning Algorithm for Modelling Robot Manipulator Dynamics using Network Inversion

Electrochemical noise measurements were taken in a 7.5 cm diameter, 10 m long multiphase oil/water/gas flow system. Full pipe flow studies were conducted for liquid velocities of 0.8, 1.0 and 1.5 m/s and slug flow for Froude numbers 4, 6, 9 and 12, using two phase (ASTM standard saltwater and carbon dioxide gas) and three phase (oil of 2cP viscosity, saltwater and gas) flow. The pressure was maintained at 134 KPa and temperature at 40 C. Noise data was measured with a Zero Resistance Ammeter and analyzed using software provided with the instrument. The noise fluctuations show trends which can be related to the type of How. Full pipe flow studies show random fluctuations around the mean for both potential and current noise.This implies the occurrence of uniform corrosion. The Fast Fourier Transform (FFT) shows roll-off greater than -40 dB/decade in magnitude, characteristic of uniform or general corrosion. In slug flow the potential noise fluctuations take the form of characteristic transients. The frequency of these transients correspond to the observed frequency of slugs. The FFT of this data shows roll-off slopes less than -20 dB/decade shown to be characteristic of pitting corrosion. A second slope of magnitude greater than -30 dB/decade is observed at higher frequencies and this might signify the presence of a second time constant controlling the corrosion reaction. This is due to the unique mechanisms associated with the mixing zone of slugs. Peaks in the Fast Fourier Transform (FFT) are also seen at particular frequencies. One of these corresponds to the slugging frequency. An increase in the percent change in standard deviation of current with Froude number implies enhanced corrosion activity on the surface of the electrode. The electrochemical noise technique is extremely useful for studying corrosion mechanisms and flow parameters in multiphase flow pipelines. Its ability to isolate dynamic incidents and study them both in the time and frequency domain makes it a powerful tool for gaining an insight into mechanistic information on corrosion in multiphase pipelines. © 1996 by NACE International.

NACE - International Corrosion Conference Series

Use of electrochemical noise to monitor multiphase flow and corrosion

In the present paper a comparative performance of the SVS auxiliary controllers for the dynamic performance enhancement of long transmission lines with and without series compensation has been evaluated. A new controller, namely, combined reactive power and frequency (CRPF) auxiliary controller has been developed and incorporated in the SVS control system located at the middle of the transmission line. The proposed SVS auxiliary controllers, considerably, enhances the system damping and the unstable system modes are stablized. A digital computer simulation study, using a nonlinear system model, has been performed to illustrate the performance of the proposed controller.

Journal of the Institution of Engineers (India): Electrical Engineering Division

SVS Auxiliary Controllers to Improve the Dynamic Performance of Long Transmission Lines with and without Series Compensation

In this paper a novel concept of a static var system (SVS) auxiliary controller application for damping subsynchronous resonance in power systems has been proposed and demonstrated. An SVS controller, known as the combined reactive power and frequency (CRPF) auxiliary controller has been developed and incorporated in the SVS control system located at the middle of a series compensated long transmission line. The studies are conducted on a system having a similar spread of the torsional modes as the first IEEE benchmark model. The proposed SVS auxiliary controller stabilizes all the torsional modes over a wide operating range. A digital computer simulation study has been performed, using a nonlinear system model, to illustrate the effectiveness of the proposed SVS auxiliary controller.

Electric Power Systems Research

Application of an auxiliary controlled static var system for damping subsynchronous resonance in power systems

In this letter we demonstrate that a photothermal microscopy experiment can be used to determine the electronic diffusivity (or carrier mobility) in the same way it is now widely used to measure locally thermal diffusivity of various nonsemiconductor materials. The main difficulty lies in the fact that in order to separate thermal and carrier diffusion, the experiment must be performed for a relatively large distance between the pump and probe beams. Photothermal signals are therefore rather weak and great experimental care must be taken. We present and discuss experimental results on Si. © 1996 American Institute of Physics.

Applied Physics Letters

Electronic diffusivity measurement in silicon by photothermal microscopy

A novel ultrasonic flow metering system been developed that has the capability of measuring liquid film thicknesses of the order of 0.1 mm and mist contents in gas flow of 4-5%. The principle of this nonintrusive technique is based on recording the transit time and attenuation of ultrasonic signals in both axial and radial directions using sets of upto eight transducers flush-mounted on the outside pipe wall at intervals around the pipe circumference and at two locations along the pipeline. The data from the meter is then used in existing multiphase flow models developed at the Corrosion in Multiphase Systems Center, to predict the quality of the gas and flow rate of the individual phases as a function of time.

American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED

Development of a novel non-intrusive, ultrasonic flow meter for wet gas pipelines

This paper presents a novel synchronous dc link voltage notching circuit topology for zero voltage switching (ZVS) of PWM inverters. The link voltage will fall to zero almost immediately after the controlled switch is turned on. Thus, the synchronous operation of the link voltage with any PWM pattern is facilitated. Analysis and simulation have demonstrated the successful operation of the new topology. The feasibility of the proposed scheme is experimentally verified on a laboratory prototype.