Abstracts

 
1 A new algorithm for fast retrieval of sequence components in 3-phase networks
Chunlin Li; Dawson, F.P.

The paper presents a new microprocessor based technique for fast retrieval of the current and voltage sequence components based on symmetrical component theory. The two-sample delay algorithm can operate at an arbitrary sampling frequency and executes with minimal computational burden. A three-point median filter is utilized to remove the impulsive noise that appears during the transient process. Simulations show that an optimal transient performance can be achieved using the proposed technique under unbalanced situations. Finally, a field programmable gate array (FPGA) implementation has been constructed to verify the theoretical results.

2 Synchronization to utility network signals containing a high level of disturbances
Pavljasevic, S.; Dawson, F.

This paper presents a digital signal processing system for synchronization to AC utility network signals containing a high level of disturbances. The system is based on a multirate phase-locked loop (PLL). The main advantages of the multirate approach are that it relaxes the implementation of the antialiasing filter and it enables one to accommodate the varying amplitude of the input signals. The antialiasing filter, which is in this case a high order bandpass filter, is implemented in the digital part of the system. This feature is achieved by applying the oversampling technique to the input signal. The antialiasing filter automatically adapts to the input signal frequency through the system's variable sample rate operation. The paper deals with modeling, analysis and implementation issues of the proposed system. Nonlinear and linear state-space models and a transfer function model are derived. The system's control aspects are discussed using the derived transfer function model. The implementation issues are presented and a digital signal processor based implementation algorithm is given. Tracking properties of the implemented system are tested with realistic signals such as a sinusoidal signal containing notch type disturbance and noise and an arc furnace voltage signal.

 
3 Phase synchronization using zero crossing sampling digital phase-locked loop
Pavljasevic, S.; Dawson, F.
The main objective of this paper is to analyze a zero crossing sampling digital phase-locked loop (PLL) as a building block for a phase synchronization system. To that purpose, the paper deals with modeling, analysis and implementation issues of the PLL. Derived are nonlinear and linear state-space models and a transfer function model. Operation of the PLL is also analyzed using frequency domain methods. An implementation of the PLL using a digital signal processor is described. On the basis of the derived models, two different system controllers are designed and the system transient response for the two cases is compared. The first controller is of a proportional-integral (PI) type and the second controller is minimum response time controller. It is shown how the input signal amplitude variations affect the system transient response. A solution for solving this problem is presented.

4  Design improvements to a three-material passive magnetic current limiter
Calman, S.; Dawson, F.P.; Yamada, S.; Iwahara, M.

This paper shows that flux nonuniformity in a passive magnetic fault current limiter softens the transition characteristics from the saturated to the unsaturated state. Soft transition characteristics lead to higher core losses and a derating in the maximum nominal operating current. Flux uniformity is improved by using a combination of extended magnets and an anisotropic saturable core. The use of distributed permanent magnets or an extended magnet leads to larger differential inductance ratios.

5  Preparation and characterization of polymer-coated magnetic nanoparticles
Burke, N.A.D.; Stover, H.D.H.; Dawson, F.P.; Lavers, J.D.; Jain, P.K.; Oka, H.

Composite materials consisting of polystyrene-coated iron nanoparticles were prepared by the thermal decomposition of iron pentacarbonyl in the presence of polystyrene-tetraethylenepentamine dispersants. The nanocomposites contain both simple core-shell particles of 10-20 nm diameter, and more complex particles (20-100 nm) made from the agglomeration of several core-shell particles. Electron diffraction revealed that the core was composed of iron, in contrast to the iron nitride (Fe/sub 3/N) reported for similar conditions with a polyisobutylene-based dispersant. The materials exhibit hysteresis and /spl sigma//sub s/ ranges from 7.6 to 29.3 emu/g. The coercivity goes through a maximum for particles of /spl ap/25 nm diameter. Removal of unbound dispersant from the materials greatly increases the magnetization.

6  Analysis and modeling of a Rosen type piezoelectric transformer
Syed, E.M.; Dawson, F.P.; Rogers, E.S., Sr.

This paper presents an equivalent circuit model for a Rosen type piezoelectric transformer. Transmission line equations for both the thickness and longitudinal modes with a clamped boundary condition on one end of each section are developed. The partial expansion theorem is used to convert the transmission line model into an equivalent circuit model. Losses are introduced in a post-processing step using the experimental value of mechanical quality factor. L'Hospital's rule is used to simplify the circuit near a resonance frequency. Experimental results confirm the existence of multimode resonance and anti-resonance behavior.

7  A robust digital current control method for active power filters
Sedighy, M.; Dewan, S.B.; Dawson, F.P.

A robust digital current control strategy for active power filters using voltage-source converters is presented. The proposed control system is designed and implemented in the form of an internal model control structure and takes the presence of computational time-delay into account. As a result, it provides an effectively overshoot-free reference-to-output response. The stability of the closed-loop system has much lower sensitivity with respect to parameter uncertainties compared to the case when a conventional predictive controller is used. The experimental results obtained from a digital-signal-processor-based single-phase experimental active power filter are also reported.

8  A novel compact magnetic current limiter for three phase applications
Mukhopadhyay, S.C.; Dawson, F.P.; Iwahara, M.; Yamada, S.

The fabrication and development of a novel compact three phase magnetic current limiter consisting of permanent magnets (PM) and saturable cores is described in this paper. Simulation results using the tableau approach are presented for varying operating conditions. Experimental results are in good agreement with the simulation results. The proposed current limiter has potential in moderately low voltage applications.

9  Investigation on the topological configuration of magnetic current limiter for the protection of power semiconductor devices
Mukhopadhyay, S.C.; Dawson, F.P.; Iwahara, M.; Yamada, S.

This paper describes different topological configurations for a passive magnetic current limiter consisting of a permanent magnet and saturable core. The fabricated model for a series/parallel biasing mode, and single/three phase supply system is described. The transient simulation has been carried out with the help of the tableau approach and experiments have been performed to validate the simulation results. The feasibility of applying the current limiter for the protection of power semiconductor devices in moderately low voltage applications is investigated.


10  Analysis, design and experimental results for a passive current limiting device
Mukhopadhyay, S.C.; Dawson, F.P.; Iwahara, M.; Yamada, S.
The authors report on the development of a passive magnetic fault current limiter (FCL) with the following attributes: compactness; small size; reliable and fail-safe operation; and zero reset time. The limiter consists of two magnetic devices connected in series and in magnetic counter opposition to each other. Two designs are considered. In one design, Nd-Fe-B permanent magnets are sandwiched between the pole faces of two saturable ferrite E-cores. In the other design, Nd-Fe-B permanent magnets are sandwiched between the pole faces of two steel E-cores with built in zones of constriction. A design procedure is developed and a design example for the ferrite and steel based core is illustrated. The transient performance of both FCL designs is simulated by means of the tableau approach. Experimental results for both designs are presented to verify the validity of the proposed tableau approach, the design procedure and the functional operation.

11  Variable-sample-rate delayless frequency-adaptive digital filter for synchronized signal acquisition and sampling
Dawson, F.P.; Klaffke, L.
In this paper, a hardware-based variable-sample-rate delayless frequency-adaptive cascaded digital filter is proposed. The open-loop frequency-adaptive and delayless property of a cascaded filter consisting of a median filter of length 3, a Blackman bandpass filter of length 30 and a predictive filter of length 25 is experimentally verified. Simulation results illustrating the filter's output response to input disturbances, in a synchronization signal acquisition application, are also presented.

12  Development of passive fault current limiter in parallel biasing mode
Iwahara, M.; Mukhopadhyay, S.C.; Yamada, S.; Dawson, F.P.
So far literature reports on the magnetic fault current limiter (FCL) are based on the series biasing mode in which the flux due to line current flows through the permanent magnet. As a result there is a high possibility of demagnetization of the permanent magnet. A passive fault current limiter is a combination of passive elements such as permanent magnet and saturable core. The permanent magnet is used to bias the core. In order to avoid severe demagnetization of the permanent magnet, we have investigated the performance of passive fault current limiters based on permanent magnet and saturable core in parallel biasing mode. The functional characteristics have been analyzed by Tableau approach and the simulation results are presented, The experimental results for a small scale prototype model are also presented for verification.

13  Transformer design considerations for mitigating geomagnetic induced saturation
Viana, W.C.; Micaleff, R.J.; Young, S.; Dawson, F.P.; Dick, E.P.
This paper shows that the placement of an auxiliary winding, used to compensate for GIC, significantly influences its rating and that of the associated DC power supply. This paper considers stresses in a banked step-up transformer under system fault conditions. Finite element simulations using the commercially available software package Magnet 5.2 are used to calculate the magnetic flux density distribution and the induced winding voltage per turn under the worst case condition of a short circuited high voltage winding. The variation in the induced voltage is greater if the winding is moved up from its optimal position and less if the auxiliary winding is moved towards the geometric centre of the transformer.

 

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