Edward Palmer

Modal estimates from normal operation of power systems

Oscillation frequency and damping of interconnected power systems have traditionally been determined from line switching or generator tripping. In a competitive environment, scheduling generation and limiting transfers to ensure the system remains stable bring cost impacts for the test. Another factor influencing the test is that the resulting oscillation must be significantly above the noise level from customer load variations. Examination of normal operation angle measurements across 1200 km in Queensland and power measurements in Victoria show that frequencies and damping of the modes can be determined. This paper presents a method for extraction of impulse response parameters with particular emphasis on separation of the modes close in frequency.

Axial Magnetic Bearing Development for the BiVACOR Rotary BiVAD/TAH

A suspension system for the BiVACOR biventricular assist device (BiVAD) has been developed and tested. The device features two semi-open centrifugal impellers mounted on a common rotating hub. Flow balancing is achieved through the movement of the rotor in the axial direction. The rotor is suspended in the pump casings by an active magnetic suspension system in the axial direction and a passive hydrodynamic bearing in the radial direction. This paper investigates the axial movement capacity of the magnetic bearing system and the power consumption at various operating points. The force capacity of the passive hydrodynamic bearing is investigated using a viscous glycerol solution. Axial rotor movement in the range of ±0.15 mm is confirmed and power consumption is under 15.5 W. The journal bearing is shown to stabilize the rotor in the radial direction at the required operating speed. Magnetic levitation is a viable suspension technique for the impeller of an artificial heart to improve device lifetime and reduce blood damage.

A high impedance fault detector using a neural network and subband decomposition

High impedance faults (HIFs) are not easily detectable using conventional overcurrent protection relays. The fault current for HIF is usually less than the normal load current, thus the overcurrent relays cannot easily distinguish HIFs from normal currents. A new method based on a subband decomposition of the current is presented. The energies from the different subbands are used as input to train an artificial neural network (ANN) for the detection of HIFs. The technique, not only detects HIF faults, but also classifies the signals into one of several classes. The main advantage of this method is that it is less sensitive to noise and HIF can be distinguished from similar events, even in the presence of high levels of noise.

Transient Stability Improvement Through Wide-Area Controlled SVCs

This paper presents a wide-area control approach to improve the transient stability of the power systems while also damping the post-fault inter-area oscillations. The proposed approach employs a nonlinear Kalman filter to estimate the inter-area modes using phasor measurement units (PMUs). The wide-area control system then uses the estimated inter-area dynamics through the developed control algorithms to improve the first swing and damping stability of the system. The performance of the proposed approach is evaluated on the simplified Australian test system with different load models including induction motors and the results show significant improvement in the stability of the system by simply adding the wide-area control signals to the available controllers in the system. The application of the proposed wide-area control system is shown to be feasible on realistic systems by improving the system stability and efficiency.

Energy function for power systems with transmission losses

Stability analysis of nonlinear systems draws heavily on energy functions. For power systems, energy functions have been developed for single machine systems and for the special case of constant power loads and lossless transmission lines, extended to multimachine systems. In this paper a circuit energy approach is reconciled with the traditional machine equations using the steady state solution for the transmission network. Physically based development of the energy function starts from the model analysed in a stationary reference frame. The monotonic convergence of the energy is demonstrated on a 3 machine system with transmission losses.

Wide-area control of aggregated power systems

This paper proposes a new method for stabilizing disturbed power systems using wide area measurement and FACTS devices. The approach focuses on both first swing and damping stability of power systems following large disturbances. A two step control algorithm based on Lyapunov Theorem is proposed to be applied on the controllers to improve the power systems stability. The proposed approach is simulated on two test systems and the results show significant improvement in the first swing and damping stability of the test systems.

The BT product as a signal dependent sample size estimate in hypothesis testing: an application to linear/nonlinear discrimination in bandwidth limited systems

This paper investigates the ability of the effective bandwidth-duration (BT) product to improve the accuracy of statistical hypothesis testing on bandwidth limiting systems by estimating the sample size of the signal. To this end, the proposition that the traditional method of assuming the sampled signal length as statistical sample size may be misguided. Simulations between a BT product sample size estimate (BT-estimate) and a discrete signal length sample size estimate (N-estimate) are compared. The BT-estimator outperforms the N-estimator for the two hypothesis tests trialled; the Lilliefors and Bera-Jarque Gaussianity tests. In simulated results the BT-estimator provides an average 19% increase in available signal bandwidth compared to the N-estimator. Physical results show that the BT-estimator improves the detection rate by 31% compared to the N-estimator. The effective BT product of a signal provides a more accurate estimate of the statistical sample size than the discrete signal length for low bandwidth to Nyquist frequency ratio signals. This result improves the accuracy (54% ) of statistical detection of linearity in bandwidth limited systems.

Power system stability enhancement using flux control for excitation system

This paper proposes a new controller for the excitation system to improve rotor angle stability. The proposed controller uses energy function to predict desired flux for the generator to achieve improved first swing stability and enhanced system damping. The controller is designed through predicting the desired value of flux for the future step of the system and then obtaining appropriate supplementary control input for the excitation system. The simulations are performed on Single-Machine-Infinite-Bus system and the results verify the efficiency of the controller. The proposed method facilitates the excitation system with a feasible and reliable controller for severe disturbances.

Interpreting regional frequencies from synchronized phasor measurement in multi-area power systems

In this paper a new approach is proposed for interpreting of regional frequencies in multi machine power systems. The method uses generator aggregation and system reduction based on coherent generators in each area. The reduced system structure is able to be identified and a kalman estimator is designed for the reduced system to estimate the inter-area modes using the synchronized phasor measurement data. The proposed method is tested on a six machine, three area test system and the obtained results show the estimation of inter-area oscillations in the system with a high accuracy.

The use of siemens PTI PSS/E in undergraduate teaching at central Queensland university

This paper describes the use of PSS/E in undergraduate teaching at CQU in third and fourth year power systems classes and in final year projects. As an industry standard power systems analysis package it has been used to not only assist students in gaining competency in the application of concepts of power system analysis and dynamics but also as a means of maximising their job readiness. For this reason it has been well received by students.