# The Power Quality Standards Force To Limit Computer Science Essay

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## Abstract

Power quality standards force to limit the total harmonic distortion (THD) within acceptable range caused by rapid usage of power electronic equipment. Therefore the main purpose of this thesis is to widen the investigation of the quality problems in power system. Where the none-linear loads are increased dramatically in recent years and turn out to is cost affected. Most of the pollution issues created in power systems are due to the non-linear characteristics and fast switching of power electronic equipment. Power quality issues are becoming stronger because sensitive equipment will be more sensitive for market competition reasons, equipment will continue polluting the system more and more due to cost increase caused by the built-in compensation and sometimes for the lack of enforced regulations. Efficiency and cost are considered today almost at the same level. Active power filters have been developed over the years to solve these problems to improve power quality. Among which shunt active power filter is used to eliminate and load current harmonics and reactive power compensation.

In this work introduces a new method for the design analysis of shunt Active Power Filter (APF) in p-q instantaneous theory and using hysteresis current band to obtain the gating signals for flying capacitor multilevel inverter (FCMLI) and Fuzzy logic controller to compensate the reactive power. The proposed active power filter is employed to reduce the current Total Harmonic Distortion (THD) drawn by the non- linear load and improve the power factor of the load. Also, this work explores the behavior of the control approaches for real time current compensation harmonics.

The advantage of fuzzy control is that it is based on linguistic description and does not require a mathematical model of the system. The compensation process is based on sensing line currents only, an approach different from conventional methods, which require sensing of harmonics or reactive power components of the load.

A MATLAB/Simulink software program has been developed to check proposed design; the Active power filter system was simulated in Matlab/simulink application. Simulink is a simulation tool based on the Matlab mathematical computing package in the time domain. Under the simulink environment, the user is able to model detailed equations of the system under study by using a wide range of graphical building blocks including control system notations, equations, and state-space representations for various models such as power-electronic devices and control circuit. Since -Matlab/Simulink provides full capabilities required for accurate simulation of all test cases in the study, they are adopted to validate this work.

## Keywords

Keywords: Active power filter (APF), Flying capacitor multilevel inverter (FCMLI), Hysteresis band controller, Harmonic compensation, Total Harmonic Distortion (THD), Fuzzy logic controller

Chapter One: Introduction

Background.

Shunt active power filter.

Five level diod clamped inverter.

Instantaneous Real and Reactive Power Method (p-q).

Fuzzy Logic Current Controller.

Hysteresis band current controller.

Problem statement.

Aims and objectives.

Project Outlines.

## Chapter One: Introduction

## Background

One of the most serious problems in electrical power systems is power quality distortion due to the Increase of nonlinear loads drawing non sinusoidal currents. Active filters which used widely for harmonic mitigations as well as reactive power compensation, load balancing, voltage regulation, and voltage flicker compensation. In three-phase four-wire systems with nonlinear loads a high level of harmonic currents in both the three line conductors and more in the neutral wire has been enrolled. Unbalanced loads also results in further declination of the supply quality. Various harmonic mitigation techniques proposed to reduce harmonics effect.

The most popular APFs is the shunt active power filter, these techniques include phase multiplication, passive filters, active power filters (APFs), and harmonic injection. It is mainly a current source, connected in parallel with the non-linear loads. Conventionally, shunt APF is controlled in such a way as to inject harmonic and reactive compensation currents based on calculated reference currents. The injected currents are meant to cancel the harmonic and reactive currents drawn by the nonlinear loads. Recently, fuzzy logic controller has generated a great deal of Interest in various applications and has been introduced in the power electronics field [1].

According to several control strategies which have been developed but still two control theories methods are always dominant, instantaneous active and reactive currents (id-iq) method and instantaneous active and reactive power (p-q), mainly. The proposed work will concentrate on two control strategies (p-q and Id-Iq) with fuzzy controller, to validate current observations. Extensive simulations are carried out with fuzzy controller for both p-q and Id-Iq methods for different voltage conditions like sinusoidal, non-sinusoidal, and un-balanced conditions to adequate results. On watching the performance of Id-Iq control strategy with fuzzy controller is quite good over p-q control strategy with fuzzy controller [2].

## sHunt active power filter

In a development electrical distribution system, there has been a sudden increase of nonlinear loads, such as power supplies, rectifier equipment, domestic appliances, and adjustable speed drives (ASD), etc.

As the number of these loads increased, harmonics currents generated by these loads may become very significant. These harmonics can lead to a variety of different power system problems including the distorted voltage waveforms, equipment overheating, malfunction in system protection, excessive neutral currents, light flicker, inaccurate power flow metering, etc. They also reduce efficiency by drawing reactive current component from the distribution network [3].

Figure (1) illustrates the concept of the harmonic current cancellation so that the current being supplied from the source is sinusoidal, the voltage source inverter used in the active filter makes the harmonic control possible.

Active power filters (APFs) have been developed. The voltage-source inverter (VSI) based shunt active power filter has been used in recent years and recognized as available solution the control scheme, in which the required compensating currents are determined by sensing line currents only, which is simple and easy to implement. [4]

Figure 1: Shunt active filter[3].

## Flying capacitor multilevel inverter (FCMLI):

Figure (2) shows a topology for five-level flying capacitor multilevel converter circuit. Multilevel Flying Capacitor Converter (FCC) topology has been recently introduced and it present advantages and disadvantages compared with other multilevel to apologies. FCC topology uses several floating capacitors in each phase that connect several points in the converter to achieve different voltage levels in the output signals.

The flying capacitor multilevel converter is a recently developed converter topology assuring a flexible control and modular design. Flying capacitor multilevel converter requires a balanced DC voltage distribution. This can be realized by using a special control leading to natural balancing or by measuring the voltages and selecting the appropriate switching state.

The balancing is influenced by three factors, namely the harmonic content of the reference waveform, the switching frequency and the load impedance. [5].

In addition to the voltage balancing of the flying capacitor multilevel converter, the output voltage must ensure the control of the load, e.g. a three phase AC machine

Figure 2: Five-level flying capacitor multilevel converter circuit topology [5]

## Instantaneous Real and Reactive Power Method (p-q)

The active filter currents are obtained from the instantaneous active and reactive powers p and q of the non-linear load. Transformation of the phase voltages Va, Vb, and Vc and the load currents Ia, Ib, and Ic into the á - â orthogonal coordinates are given in Equation (1 and 2).

The compensation objectives of active power filters are the harmonics present in the input currents. Present architecture represents three phase four wire and it is realized with constant power controls strategy. The power calculation is given in detail form in Equation (3) [6][7].

= (1)

= (2)

= (3)

= (4)

## Fuzzy Logic Current Controller

Fuzzy logic uses fuzzy set theory, in which a variable is a member of one or more sets, with a specified degree of membership. Fuzzy logic allow us to emulate the human reasoning process in computers, quantify imprecise information, make decision based on vague and in complete data, yet by applying a "defuzzification" process, arrive at definite conclusions. The block diagram representation of fuzzy logic controller (FLC) is shown in Figure 3 [8].

Figure 3: Block diagram of FLC[8].

The FLC mainly consists of three blocks:

â€¢ Fuzzification.

â€¢ Inference.

â€¢ Defuzzification.

The details of the above processes are given below:

## A. Fuzzification

The fuzzy logic controller requires that each input/output variable which define as the control surface be expressed in fuzzy set notations using linguistic levels. The linguistic values of each input and output variables divide its universe of discourse into adjacent intervals to form the membership functions.

The member value denotes the extent to which variable belong to a particular level. The process of converting input/output variable to linguistic levels is termed as fuzzification.

## B. Inference

The behavior of the control surface which relates the input and output variables of the system is governed by a set of rules. A typical rule would be

If x is A, Then y is B, when a set of input variables are read each of the rule that has any degree of truth in its premise is fired and contributes to the forming of the control surface by approximately modifying it. When all the rules are fired, the resulting control surface is expressed as a fuzzy set to represent the constraints output. This process is termed as inference.

## C. Defuzzification

Defuzzification is the process of conversion of fuzzy quantity into crisp quantity. There are several methods available for defuzzification. The most prevalent one is centroid method, which utilizes the following formula:

âˆ« (Âµ (x) x) dx / âˆ«Âµ (x) dx, Where ì is the membership degree of output x [9].

## hysteresis band current controller

The hysteresis band current control technique has been proven to be most suitable for all the applications of current controlled voltage source inverters in active power filters. And it's implemented to generate the switching pattern in order to get precise and quick response. The hysteresis band current control is characterized by unconditioned stability, very fast response, and good accuracy [10]

## Problem statement

The problem of this project is to study the power quality distortion due to the Increase of nonlinear loads drawing non sinusoidal currents problem and find solution for this problem by using shunt active power filter, these techniques include phase multiplication, passive filters, active power filters (APFs), and harmonic injection which is describe by fuzzy logic controller.

## Aims and objectives

Power quality standards force to limit the total harmonic distortion (THD) within acceptable range caused by rapid usage of power electronic equipment. Therefore the main purpose of this thesis is to widen the investigation of the quality problems in power system. Where the none-linear loads are increased dramatically in recent years and turn out to is cost affected. Accordingly the proposal of this work will go through following steps to validate our objectives

Design and analysis a five-level flying capacitor multilevel inverter circuit to apply an equal but opposite to the distorted harmonics in to the line of source current to cancel the non-linear load harmonics.

Design a fuzzy logic controller requires controlling the capacitor Dc voltage to improve the time response of the shunt active power system.

Visualize on the simulation of instantaneous active and reactive theory based shunt active filter with MATLAB/ Simulink, as a better solution for reduction of the harmonics

Simulations will carry out with fuzzy controller for both p-q methods.

Analyze the obtained result.

## Project Outlines

This research report will be divided to many chapters; five chapters will be combined with each other and organized as follow:

Chapter 1: is an introduction about shunt active filter, this chapter gives an introduction that includes the scene of the project, explain the terminology, and outline the goals that the project will revolve around and cover some of the methodology and techniques that will be used in its production.

Chapter 2: will explore the introduction to shunt active filter and P-Q theory in general, and contains a literature review about this approach.

Chapter 3: will discuss the design and analysis of the system, this chapter will contain system design and program design. This chapter will be based upon the screen shots of the project, all the screen shots of the simulation design.

Chapter 4: explores the results which have been derived with simulation/analysis and measurements.

Chapter 5: contains the conclusion of research work and the suggested future work.

Chapter Two: Literature Review

Shunt active filter based on d-q theory and fuzzy logic.

flying capacitor converter and hysteresis controller.

Chapter Two: Literature Review

Shunt active filter based on d-q theory and fuzzy logic.

Fuzzy logic controller applied and extended to a three level shunt APF is proposed in [11], fuzzy logic control algorithm is proposed for harmonic current and inverter dc voltage control to improve the performances of the three levels active power filters and shows how we can use the three-level inverter as a shunt active power filter.

The original instantaneous reactive power theory or p-q theory has been systematically used in the control of active power filters (APFs). When the APF is connected in parallel to a non-linear and unbalanced load, the p-q theory application has allowed a compensation strategy named constant power to be obtained in [12] shows that any compensation strategy may be developed into the p-q theory frame, besides, on p-q theory reformulation without using mapping matrices.

In [13], shows how shunt Active Power Filter (APF) for power quality improvements in terms of harmonics and reactive power compensation in the distribution network by Integral (PI) or Fuzzy Logic Controller (FLC).

In [14], the electric network behaves as an ''healthy carrier'' of disturbances, and this disturbance generated by one customer can be distributed to other customers, causing possible damage to their equipment, the measurement of the quality.

In [15], describes the development of a low cost shunt active power filter with digital control, which allows dynamic power factor correction and both harmonics and zero-sequence current compensation. The active filter controller is based on the instantaneous power theory (p-q theory).

In [16], the structure of a fuzzy PID controller is presented. The application of the fuzzy logic controller as a power system stabilizer is investigated by means of simulation studies on a single machine infinite bus system.

In [17] Describe harmonic problem and find solution for this problem by using shunt active power filter with three levels which is controlled by using fuzzy logic controller. The active shunt power filter making important work to solution the quality problem which can do compensation on the harmonic current which is delivered by nonlinear load and also compensate the reactive power. By [17] the active shunt filter which use to solve harmonic problem is using by three phase of voltage and evolved by using the strategy that very important after the P-Q theory is applied. P-Q theory is tool to calculation the amount of current must be applied to compensate.

In [18] Talking about optimal design of fuzzy logic controller about shunt active filter and how could be controlled. This design is very important for harmonic compensation which serves the power quality. The [18] work based by two cases, the first one that this system is design and controlled by fuzzy logic controller and the rules are using in this design is accordingly robust. In the second one the membership function of this system and the normalization of gain are comprehend by optimal Ant Colony method which describe in [18].

As describe in previous section that the non-sinusoidal current is increased in the last year this non-sinusoidal current comes from harmonic that produced by non-linear load. Shunt active filter is used to eliminate the harmonic current that causes. Shunt active filter criteria based in two cases: the first case that the shunt active filters accepted the dc connection voltage, in second case, shunt active filter decide the harmonic which will be eliminating [18].

The idea of Fuzzy Logic (FL) planned Lotfi Zadeh in 1965; at initial as a method of dispensation data by allowing incomplete situate membership quite than crisp membership. Before long after, it was established to be admirable selections for some organize system applications because it mimic individual control logic. Fuzzy controller work as converter from linguistic manage stratagem to automatic manage strategy. The fuzzy rules are constructed by specialist knowledge database. Initially, the error e (t) and the difference error âˆ†e (t) have been located of the angular velocity. So the output of the fuzzy controller is obtainable controlling the voltage u (t).

IN [19] they use the increasing in power quality problem that cause by large number of nonlinear load in electronic device. And the voltage harmonic problem and the power equipments of power distribution system comes from the harmonic current that cause by nonlinear device. When the harmonic current are produce the nonlinear current flow in the transmission line and enter to the electrical device, so additional distortion on voltage are produced leading that to ensure that any operation in power system grid such that generates , transmission and distribution the distortion current and voltage are increase producing.

Significant problems normally caused in 3-phase 4-wire system. As clear when the harmonic current problem are caused the ground line which called the cold line may be go to overheated and fire. So the needed to perfect compensator are necessary available. More than one technology used to solve and control this huge problem one of that technologies are describe in [19].

The major aim [19] is to build up Fuzzy controller to study and describe the performance of instantaneous (id-iq) control plan for extort reference currents with balanced and unbalanced voltage situation by use shunt active filters, If the voltage of supply is sinusoidal or in balance, the criteria of control join in the similar. In other hand, when the voltages of supply are unbalanced or distorted, the criteria of control go in different criteria of harmonic compensation. The p-q theory which used particularly is not enough to find an optimal solution when the voltage of supply is not perfect. The [19] use fuzzy logic controller of Id-Iq under dissimilar voltage. And the system implemented system contains 3-ph 4-wire with shunt active filter.

2.2 FLYING CAPACITOR CONVERTER AND Hysteresis Controller.

In [20] shows the feature of a flying capacitor converter is the natural voltage balance property. The reported voltage balance dynamics analytical research methods are based on heavy frequency domain transformations (Fourier transform, Bessel functions) and are rather algorithmic and difficult to use in an everyday engineering practice. Suggested time domain approach uses stitching of piece-wise analytical solutions for consecutive switching intervals. The small parameter analysis of a five-level single-leg converter yields physically meaningful, simple, and accurate expressions for average voltage balance dynamics giving an in-depth insight into parameters, carrier frequency, and modulation strategy impact for both DC and AC PWM.

For a DC modulated five-level single-leg FC converter, simple and accurate expressions for voltage balance natural frequency and time constants and capacitor voltage balance dynamics were obtained by applying the time domain analysis technique and utilizing the small parameter naturally arises for practical converters with low current and voltage ripples. The frequency and time constants formulas along with the average voltage balance dynamics expressions clearly reveal the dependences on inductive load parameters, carrier frequency, voltage command, and modulation strategy.

An insight into the voltage balance mechanism gained from

DC PWM consideration is definitely useful for AC PWM as well. Accurate AC PWM frequency and time constants dependences on modulation index are obtained by averaging on AC fundamental period. Practically, AC fundamental frequency has no impact on voltage balance dynamics.

In [21] a three-level inverter based Shunt Active Power Filter (SAPF) using Multi-Level Hysteresis Current Controller (MLHCC) is presented for solution of power quality problems in distribution system. A simulation model of SAPF is prepared in Matlab/Simulink environment. MLHCC is used for control of SAPF currents. In simulation study, it is considered that SAPF executes two tasks covering compensation of harmonics and reactive power. Therefore, control algorithm is formed to execute two tasks. The Synchronous Reference Frame Method (SRFM) is used to extract the reference currents. Dynamic performance of SAPF is evaluated using two nonlinear loads switched at different times. Some simulation results are given to show performance of a three-level inverter based SAPF using MLHCC. Simulation results show that current harmonics has been kept inside specific recommendation of IEEE-519 and ac grid is approximately kept in unity power factor.

In [22] presents a comprehensive design and simulation of three-phase shunt active power filter to compensate the harmonics of nonlinear loads. The paper describes the complete design aspects of power circuit elements and control circuit parameters. The process is based on sensing line currents, line voltages and DC side capacitor voltage to compensate the harmonics in the nonlinear load. In this paper, hysteresis current control band is used in order to obtain switching signals to compensate the harmonics. The graphical outcomes show that the active filter brings the THD of the system well below

15%, while it shows 30% THD without filter

In [23] The Shunt Active Power Filter (SAPF) is one of the key controllers in Flexible Alternating Current Transmission System (FACTS) to control the transmission line voltage and can be used in Power System (PS) to enhance the power quality. This paper compares performance of Cascaded Five-Level Inverter (CFLI) based SAPF in PS with PI, Fuzzy and Neurofuzzy controller. Making use of the CFLI has benefits of low harmonics distortion, reduced number of switches and switching losses. In order to compensate the reactive power, balance the capacitor DC voltage and suppress the total harmonics distortion (THD) drawn from a Non-Linear Diode Rectifier Load (NLDRL) of SAPF, Sub-Harmonics Pulse Width Modulation (SHPWM) technique, and D-Q reference frame theory are proposed in this paper. The SHPWM pattern generation is used as control for the switches of CFLI. The D-Q reference frame theory is used to calculate the reference compensating currents for SAPF. PI controller fuzzy and neurofuzzy controller are used for capacitors dc voltage regulation for SAPF. The results are verified and validated through MatLab/Simulink simulation software with SAPF and without SAPF.

In [24] presents Hybrid Cascaded Seven-Level Inverter (HCSLI) used in SAPF to compensate reactive power, improve the power factor and to suppress the total harmonic distortion (THD) in supply current due to linear load and Non- Linear Diode Rectifier Loads (NLDRLs).In this paper d-q reference frame theory for reference current computation, Constant Switching Frequency Multicarrier Sub-Harmonic Pulse Width Modulation (CSFMSHPWM) technique for controlling the switches of HCSLI, Fuzzy logic controller (FLC) for regulating dc side capacitor voltage are proposed.

Chapter three: System Design

Artefact design.

Execution plan of the artefact.

Overview.

The theory and device uses in the project.

Linear and non linear loads.

Total harmonic disturtions THD.

P-Q theory explanation.

Shunt active filter..

Fuzzy logic

Flying capacitor inverter.

Hysteresis band current controller.

The model of design circuit.