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Power Quality – An Integrated Perspective P. F. Ribeiro, MBA, PhD, PE Professor of Engineering Calvin College Engineering Department 0 Grand Rapids, Michigan 5 0 5 2 0 2 10 5 0 5 10 0 5 Seminario Brasileiro de Qualidade da Energia Eletrica 0 5 Outline Background What is Power Quality? Complex Issue (need for better definitions) Harmonics - What is your responsibility? Background Distortion More than Just Voltage Diviations Power Quality Cost ($$$$) Issues Advanced in Power Quality Solutions Monitoring Software (the fuzzy/neural evolution) Hardware (active compensators, switches) Concepts (Custom Power, PQ Parks, FACTS) Seminario Brasileiro de Qualidade da Energia Eletrica Outline Legal Issues Impact of Privatization and Deregulation Opportunities (differentiated power services - premium power, consulting, etc) Reliability, Quality and Price New Utility/Manufacturers Approaches (PQ Programs) Standards R &D General Principles - An Advice Conclusions Seminario Brasileiro de Qualidade da Energia Eletrica Power Quality Principles; 1. Understand the problem 2. Find the real cause before you find the best solution 3. The solution must be always cost effective 4. Be open and work closely with the customer 5. Be Pro-Active, Not Reactive 6. Do not go after magic solutions 7. Educate utility and customers 8. Offer alternative PQ Services (US, France) 9. Be aware of legal issues 10. Satisfy the customers - They are alwyas right Seminario Brasileiro de Qualidade da Energia Eletrica A Complex World: A Philosophical Reflection These things are so delicate and numerous that it takes a sense of great delicacy and precision to perceive them and judge them correctly and accurately: Most often it is not possible to set it out logically as in mathematics, because the necessary principles are not ready to hand, and it would be an endless task to undertake. The thing must be seen all at once, at a glance, and not as a result of progressive reasoning, at least up to a point. Blaise Pascal, 1650 Seminario Brasileiro de Qualidade da Energia Eletrica Advanced Power Quality Solutions Software Wavelet Theory Expert Systems Fuzzy Logic Genetic Algorithms Neural Network Seminario Brasileiro de Qualidade da Energia Eletrica Advanced Power Quality Solutions Hardware Active Harmonic Filters Micro SMES for Power Quality Large SMES for Transmission / Distribution PWM Based Higher Power Compensators FACTS Controller, Custom Power Devices Transfer Switches Seminario Brasileiro de Qualidade da Energia Eletrica Advanced Power Quality Solutions Measuring and Monitoring Artificial Inteligence Instruments Remote Access Integrated Diagnostic Comprehensive System Monitoring Centralized Monitoring (GPS) Seminario Brasileiro de Qualidade da Energia Eletrica Advanced Power Quality Solutions Systems and Concepts PQ Parks Custom Power / FACTS / Transfer Switches Higher Immunity Special Contracts Power Management Companies Seminario Brasileiro de Qualidade da Energia Eletrica The PQ Equation PowerQuality ( A B C )dPd $ A - Electric parameters B - Economic Parameters C - Structure of the Sector $ PQ Seminario Brasileiro de Qualidade da Energia Eletrica Advanced Power Quality Solutions Computer Modeling and Simulation Graphical Environment Inclusion of Artificial Intelligence (fuzzy / neural, wavelets) Integrated Economic Analysis Seminario Brasileiro de Qualidade da Energia Eletrica Standards Seminario Brasileiro de Qualidade da Energia Eletrica R&D - New Developments Seminario Brasileiro de Qualidade da Energia Eletrica Background Traditional power quality analysis tools have proven very useful in power system steady state distortion analysis. However, considering the ever growing utilization of electronically controlled loads and system devices, the consequent dynamics of distortion generation, propagation and interaction with the system, one would need a more powerful technique to efficiently analyze the system performance in the presence of non-stationary distortions. New techniques have recently unfolded which in the future may help us to better categorize and analyze in a more effective way many types of voltage distortions or power quality deviations. Seminario Brasileiro de Qualidade da Energia Eletrica Background From Precise Electronics to Fuzzy Logic Twenty years ago the power sector was having some difficulties to keep up with the growing concerns with power quality due to the rudimentary monitoring instrumentation. Now the power sector is having difficulties to cope with the amount of information generated by the new hardware and software technologies. Artificial intelligence and other advance techniques seem to be the natural way to overcome the difficulties in handling the huge amount of power quality monitoring data. Seminario Brasileiro de Qualidade da Energia Eletrica Wavelets: Analysis / Applications Impulsive transients commutation notches, etc. can be represented ,analyzed, and identified more easily and objectively -------The following possible applications are envisaged for power system analysis: * Transient Analysis; * Non-stationary Voltage Distortions; * Power Signature Recognition; * Signal/System Identification; * Non-Invasive Testing/Measurements; * Power System Analysis in General; * Integrated characterization of voltage disturbances Seminario Brasileiro de Qualidade da Energia Eletrica Wavelet Theory Making Waves: Big and Small Transient Distortion Analysis The traditional spectral (Fourier) method has some severe limitations in dealing with the new electrical environment / phenomena. Wavelets are functions localized both in time(or space) and frequency. These functions are generated from a single generating (mother) wavelet by translations and dilations. These properties make wavelets very attractive for non-stationary power quality analysis. In many cases, not only are fewer functions required with wavelets than with Fourier series, but anomalies such "Gibbs" phenomenon are reduced. Wavelets have been used effectively in applications such as multidimensional signal processing, video data compression, and reconstruction of high resolution images and high quality speech. Considering the analysis of transient signals in power systems, wavelets could be very well applied with advantages over Fourier methods. The advantage would rely on the precision and speed of the method to analyze transient signals as well as the economy of storage space). Seminario Brasileiro de Qualidade da Energia Eletrica -The Wavelet Theory Wavelet theory is the mathematics associated with building a model for a signal with a set of special signals, or small waves, called wavelets. They must be oscillatory and have amplitudes which quickly decay to zero. The required oscillatory condition leads to sinusoids as the building blocks (particularly for electrical power systems). However wavelets do not need to be damped sinusoids. Mathematically speaking, the wavelet transform or decomposition of a function, f(t), with respect to a mother wavelet, h(t), is: Wf (a , b) 1 a 1 2 t b f (t )h dt a * Seminario Brasileiro de Qualidade da Energia Eletrica I don’t get it... I’ll try later Scaled and Translated Wavelets Seminario Brasileiro de Qualidade da Energia Eletrica The inverse transform creates the original function by summing appropriately weighted, scaled and translated versions of the mother wavelet, as indicated by the following equation . The weights are the wavelet coefficients, Wf(a,b). Yes ! 1 f (t ) Ch Ch 1 t b dadb Wf (a , b) a h a a 2 1 2 h( w) dw w Seminario Brasileiro de Qualidade da Energia Eletrica Alternatively, expressing the inverse wavelet transform in a discrete form, we have: f (t ) k Wf ( m, n ) m m 2 a 0 g(a 0 m 0 n 0 Seminario Brasileiro de Qualidade da Energia Eletrica nb0 ) The Wavelet Transform Seminario Brasileiro de Qualidade da Energia Eletrica Illustration of Flexibility Original Waveform to be analyzed 2 Wavelet Components Reconstruct function Seminario Brasileiro de Qualidade da Energia Eletrica Impulsive Transient Commutation Notches Seminario Brasileiro de Qualidade da Energia Eletrica Wavelets in Power Systems? Same principle: establishing libraries of waveforms which would fit a certain type of disturbance or transient. These libraries equipped with fast numerical algorithms can enable real-time implementation of a variety of signal processing tasks. This characterization of the signal provides efficient superposition in terms of oscillatory modes on different time scales . Power Systems Applications -Transient Analysis -Non-stationary Voltage Distortions -Power Signature Recognition -Signal/System Identification -Non-Invasive Testing/Measurements -Power System Analysis in General -Integrated characterization of voltage disturbances, e.g. transients and harmonic distortions Seminario Brasileiro de Qualidade da Energia Eletrica Expert Systems Expert systems are computer systems implemented by methods and techniques for constructing human-machine systems with specialized problem-solving expertise. The rules usually take the form of "IF .... THEN ..." statements which can be chained together to form a conclusion from the data. The main drawback with expert systems is that the rules of inference must be collected from a human expert and converted to an acceptable form. Fuzzy Systems Fuzzy systems are a type of expert system but with fuzzy rules. Seminario Brasileiro de Qualidade da Energia Eletrica Neural Networks Neural networks consist of a number of very simple and highly interconnected processors called neurodes, which are the analogs of the biological neural cells, or neurons, in the brain. The neurodes are connected by a large number of weighted links, over which signals can pass. As a pattern classifier neural networks can be used for a number of PQ applications, such as waveform classification, system identification, etc. Recently neural nets have been used for waveform classification, and identification of harmonic sources where sufficient direct measurement data are not available. Seminario Brasileiro de Qualidade da Energia Eletrica Fuzzy Logic - Back To Empiricism? Not Really a Harmonic Distortion. What is the correlation between high harmonic distortions and the World Cup? This might not have been a very hard one to figure out. However, most power quality problems are not well defined or correlated with an specific cause. In many cases, it is also difficult to assign a specific number to an input value for any of a variety of reasons. Consider the set of voltage disturbances (waveform faults) collected at two different points of the electric system. Also consider that different load conditions and instruments might be used. How would these qualitative reports correspond to the actual picture of what has happened to the system. That is when the concept of fuzzy logic becomes very handy. The fuzzy principle: everything is a matter of degree, seems to fit well with many of the difficulties one faces in interpreting power quality signatures. Fuzzy logic or sets are useful anywhere measurements are imprecise or their interpretation depends strongly on context or human opinion. Fuzzy logic thus captures the system condition plus the human / instrument perception, in place of the objective measurements themselves, and thus contain both more and less information than the original measurements values. Seminario Brasileiro de Qualidade da Energia Eletrica Evolutionary Systems - Genetic Algorithms Imagine that you want to create a database to classify power quality waveform distortions. Most of the relationships seem initially obvious. But when the database grows into a large system, establishing relationships becomes an enormous job. This is corroborated by the fact that not all power quality problems are well defined. The process to establish correlation has been found to be similar to genetic reproduction. A GA provides an efficient method of searching through a wide range of possibilities. Simple GAs use three key operators to explore their search space: reproduction, mutation, and crossover. Considering the numerous conditions of the electrical parameters of a power systems it is desirable to use a mathematical tool which might concentrate on the most significant cases. GAs can be used to predict typical voltage quality deviations such as harmonic distortions and the consequent cumulative or statistical effect of many sources under numerous and dynamic system and load conditions. In a power quality case the approach could be to search out for the best combination of system variables: capacitor bank switching, load impedance levels, and the harmonic current injections. Seminario Brasileiro de Qualidade da Energia Eletrica Developing a Comprehensive PQ Waveform Identification System An integrated way to develop a comprehensive PQ identification waveform identification system would utilize a combination of: expert (fuzzy) systems wavelet theory / advanced Signal Processing neural networks genetic algorithms, etc Seminario Brasileiro de Qualidade da Energia Eletrica Conclusions PQ Will continue to grow in importance as the electric sector operates within a truly free economy. Utilities, customers and manufacturers will have to cooperate to establish a stable model for the power quality industry sector Differentiated Premium Power will Become a reality (US, France) Reliability and Quality will become as important as Price Seminario Brasileiro de Qualidade da Energia Eletrica Input Waveforms (periodic distortions) (periodic) (non stationary distortions) Spectral Analysis Wavelet Analysis (non stationary) Basic Classification of Disturbances by Expert System Advanced Classification of Disturbances By Fuzzy System (Trained by Neuro Net) Neural Network Trained to Identify Periodic and Non-Periodic Waveforms Genetic Algorithms Fuzzy Logic Load type 1 Load type 2 Neuro Net Cap. Switching Seminario Brasileiro de Qualidade da Energia Eletrica .............