29-01-2011, 11:35 AM
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CONTENTS
Introduction
Types of signal processing techniques are use
MEASUREMENT SYSTEM ARCHITECTURE AND SIMULATION
FREQUENCY MEASUREMENT.
HARMONICS MEASUREMENT
MODELLING OF THE KALMAN FILTER
FLICKER MEASUREMENT
WAVELET BASED SIGNAL DECOMPOSITION TECHNIQUE
HARDWARE PLATFORM
APPLICATIONS
CONCLUSIONS
INTRODUCTION
This presentation provides an overview of the time varying power quality issues in power systems.
A new signal processing techniques for real time measurement of various power quality parameters.
The definition of Power Quality cannot be limited to the characteristics of the supply power. The definition must also include the requirements of the load.
Signal processing techniques are applied for real time measurement of power quality parameters such as frequency, harmonics, flicker and disturbances.
Types of signal processing techniques
(1) Digital filtering technique
2) Kalman filter technique
(3) Fast Fourier Transform and statistical method
(4) Multi-resolution signal decomposition techniques
based on wavelet transform
FREQUENCY MEASUREMENT
In many power system protection and control schemes it is necessary to accurately measure and track the fundamental power frequency under sinusoidal and non-sinusoidal conditions
There are various methods
zero crossing methods
FFT leakage
Stationary phase changes
Least squares fitting.
SIMULATION RESULTS
The method has been tested under various conditions using the simulation software MATLAB.
Simulation is run for 24 hour period with new inputs every 2 minutes.
Output can be analyzed for each component individually or collectively by looking at the THD (bottom).
CASE-I
CASE -II
The method is also tested
for signals with multiple
zero crossing.
Simulation results
concludes that the
maximum error of this
model is less that 0.005% under non-sinusoidal and multiple zero crossing conditions.
HARMONICS MEASUREMENT
Due to increased utilization of power electronics devices voltage and current waveforms of a distribution or a transmission system are not pure sinusoids but consist of a combination of the fundamental frequency, harmonics and high frequency transients
The DFT and FFT transform is a useful analytical tool that has been applied to power system for phasor measurement and harmonic analysis.
FLICKER MEASUREMENT
Flicker is basically caused by fluctuations of the electrical power network that may occur at any time under the influence of the variations of any of the three components of the network
Voltage fluctuations up to 30Hz may produce annoyance even if considering small relative amplitudes such as 0.25% at the critical modulation frequency of 8.8Hz
the use of FFT and new statistical block for real time measurement of flicker in power system.
WAVELET BASED SIGNAL DECOMPOSITION TECHNIQUE
Wavelets can determine the presence of transients and harmonic distortions of very small values: up to less than 0.5%.
With values around 0.1% the detail coefficients can hardly detect the transient and harmonics.
The color map seems more helpful in identifying both transients and harmonics as the magnitude both transients and harmonics values go bellow 0.5%.
APPLICATIONS
A. Feeder Protection and Load Shedding
B. Harmonic Filter design
C. Wind Turbines.
D. Power Quality Disturbance Analysis
CONCLUSIONS
In this paper we have proposed high performance signal processing techniques and the proposed digital instrument based on multiple DSP that help to speed up measurement and algorithm execution
Power Quality has a dynamic, time-varying nature which with the increased complexity and sensitivity of equipment needs to be properly understood and addressed. Traditional methods are not sufficient.
Advanced techniques and technologies, including real real-time modeling / simulation, power electronics solutions, signal processing and controls applications are available to assist in these tasks.
