1.2 Problem Statement
‘ Harmonics is a major cause of power supply pollution
Modern electronic equipments such as personal computers, printers, copiers, medical test equipment, fluorescent lighting, adjustable speed drives and other non-linear loads generate harmonics in the electrical distribution system. There are two types of non-linear loads: single-phase and three-phase. A non-linear load consumes electricity and thus draws a non-sinusoidal current from the supply when supplied with sinusoidal voltage. The harmonic currents produced by the non-linear load generate additional losses in electrical installations and can cause thermal overload.
‘ Solution to reduce harmonics in power distribution system
There are many ways to reduce harmonics depending on the cost and load. Active Power Filter (APF) is considered to be the best solution to reduce harmonics in the power system since they have no resonance problems and are inherently current limiting.
‘ Design and Simulation of active power filter is still an issue
Even though many research and simulation based on active power filter have been done, there still have no perfect method to reduce harmonics effectively. Active power filters are still an open problem since they are limited in their frequency range and cannot handle large amount of power. They require D.C power supply for their operation.
1.3 Aims and Objectives
Aims
The main aim of this project is to explain the effects of harmonics in the power system and designing active power filters to remove high value harmonics which causes non-sinusoidal waveform.
Objectives:
‘ To study about active power filter and identify the method to reduce harmonic effects using active power filter.
‘ To design circuits of active power filter.
‘ To design and simulate single- phase shunt active power filter for harmonic reduction using Matlab/Simulink.
‘ To design and simulate three-phase shunt active power filter for harmonic reduction using Matlab/Simulink.
1.4 General structure of active filtering scheme
Active Power Filter is used to compensate current-based distortion and voltage-based distortion such as voltage harmonics, voltage sag and swells. The Active Power Filter injects equal current or voltage distortion in the network but in opposite magnitude. Thus the injected current or voltage cancels the actual distortion present in the circuit. Active Power Filter uses fast switching insulated gate bipolar transistors (IGBTs) that produce output current which cancels the original load generated harmonics when injected into the Ac lines.
Figure 1.1 shows the different component of an Active Power Filter system
Figure 1.1
Shunt Active Power Filtering (Jarupula Somlal, 2011)
In this configuration, the filter is connected in parallel with the load being compensated. The harmonic control is possible due to the voltage source inverter in the active filter. This inverter generates a signal that will cancel the harmonics from the non-linear load.
Types of active power filters
1. Shunt Active Power Filters:
It compensates current harmonics by injecting equal-but-opposite harmonic compensating current. It operates as a current source injecting the harmonic components generated by the load but phase shifted by 180deg (ARUN KUMAR N.K, 2013).
`
Figure 1.2
Compensation characteristics of active power filter (ARUN KUMAR N.K, 2013)
2. Series active power filter:
Series active power filter functions mainly as a voltage regulator and harmonic isolator between the non-linear load and the utility system. In order to protect the consumer from a poor supply voltage quality, the series active power filter is considered. The series active power filter injects a voltage component in series with the supply voltage and therefore can be regarded as a controlled voltage source, compensating voltage sags and swells on the load side (Dr. Hopkins, 2011). Figure 1.3 below shows the series active power filter topology.
Figure 1.3 Series active power filter (NUR IZZATI NADIAH BINTI ISHAK, 2010)
3. Hybrid active power filters:
Hybrid Filters are more complex filters which are made up of combination of active and passive filters. They are used for the conditions where both voltage and current are leading to deterioration in power system.
Figure 1.4
Hybrid active power filter (NUR IZZATI NADIAH BINTI ISHAK, 2010)
1.6 Dissertation Outline
Chapter 2 is about the generation of harmonics and their effects on power quality. It presents the different techniques used to mitigate harmonics. It also includes a description of how switch mode power supplies affect line voltage waveforms and power factor.
Chapter 3 consists of the design of shunt active power filter for a single phase system. The shunt active power filter is implemented using simulation scheme. All the stages in the system are thoroughly analyzed mathematically.
Chapter 4 presents the design of shunt active power filter for a three phase system. Emphasis is given on the implementation of shunt APF. It also presents the mathematical model for the current sensing stage, filter, modulator, inverter and the interconnection back to ac lines.
Chapter 5 discusses the simulation test and results for single phase and three phase shunt APF. From these results discussions are made.
Chapter 6 consists of the conclusion on the work achieved in the project and summarizes the research undertaken. It also offers recommendations for further research.
Chapter 7 contains all the references that have been used in this project.
.2 Problem Statement
‘ Harmonics is a major cause of power supply pollution
Modern electronic equipments such as personal computers, printers, copiers, medical test equipment, fluorescent lighting, adjustable speed drives and other non-linear loads generate harmonics in the electrical distribution system. There are two types of non-linear loads: single-phase and three-phase. A non-linear load consumes electricity and thus draws a non-sinusoidal current from the supply when supplied with sinusoidal voltage. The harmonic currents produced by the non-linear load generate additional losses in electrical installations and can cause thermal overload.
‘ Solution to reduce harmonics in power distribution system
There are many ways to reduce harmonics depending on the cost and load. Active Power Filter (APF) is considered to be the best solution to reduce harmonics in the power system since they have no resonance problems and are inherently current limiting.
‘ Design and Simulation of active power filter is still an issue
Even though many research and simulation based on active power filter have been done, there still have no perfect method to reduce harmonics effectively. Active power filters are still an open problem since they are limited in their frequency range and cannot handle large amount of power. They require D.C power supply for their operation.
1.3 Aims and Objectives
Aims
The main aim of this project is to explain the effects of harmonics in the power system and designing active power filters to remove high value harmonics which causes non-sinusoidal waveform.
Objectives:
‘ To study about active power filter and identify the method to reduce harmonic effects using active power filter.
‘ To design circuits of active power filter.
‘ To design and simulate single- phase shunt active power filter for harmonic reduction using Matlab/Simulink.
‘ To design and simulate three-phase shunt active power filter for harmonic reduction using Matlab/Simulink.
1.4 General structure of active filtering scheme
Active Power Filter is used to compensate current-based distortion and voltage-based distortion such as voltage harmonics, voltage sag and swells. The Active Power Filter injects equal current or voltage distortion in the network but in opposite magnitude. Thus the injected current or voltage cancels the actual distortion present in the circuit. Active Power Filter uses fast switching insulated gate bipolar transistors (IGBTs) that produce output current which cancels the original load generated harmonics when injected into the Ac lines.
Figure 1.1 shows the different component of an Active Power Filter system
Figure 1.1
Shunt Active Power Filtering (Jarupula Somlal, 2011)
In this configuration, the filter is connected in parallel with the load being compensated. The harmonic control is possible due to the voltage source inverter in the active filter. This inverter generates a signal that will cancel the harmonics from the non-linear load.
Types of active power filters
1. Shunt Active Power Filters:
It compensates current harmonics by injecting equal-but-opposite harmonic compensating current. It operates as a current source injecting the harmonic components generated by the load but phase shifted by 180deg (ARUN KUMAR N.K, 2013).
`
Figure 1.2
Compensation characteristics of active power filter (ARUN KUMAR N.K, 2013)
2. Series active power filter:
Series active power filter functions mainly as a voltage regulator and harmonic isolator between the non-linear load and the utility system. In order to protect the consumer from a poor supply voltage quality, the series active power filter is considered. The series active power filter injects a voltage component in series with the supply voltage and therefore can be regarded as a controlled voltage source, compensating voltage sags and swells on the load side (Dr. Hopkins, 2011). Figure 1.3 below shows the series active power filter topology.
Figure 1.3 Series active power filter (NUR IZZATI NADIAH BINTI ISHAK, 2010)
3. Hybrid active power filters:
Hybrid Filters are more complex filters which are made up of combination of active and passive filters. They are used for the conditions where both voltage and current are leading to deterioration in power system.
Figure 1.4
Hybrid active power filter (NUR IZZATI NADIAH BINTI ISHAK, 2010)
1.6 Dissertation Outline
Chapter 2 is about the generation of harmonics and their effects on power quality. It presents the different techniques used to mitigate harmonics. It also includes a description of how switch mode power supplies affect line voltage waveforms and power factor.
Chapter 3 consists of the design of shunt active power filter for a single phase system. The shunt active power filter is implemented using simulation scheme. All the stages in the system are thoroughly analyzed mathematically.
Chapter 4 presents the design of shunt active power filter for a three phase system. Emphasis is given on the implementation of shunt APF. It also presents the mathematical model for the current sensing stage, filter, modulator, inverter and the interconnection back to ac lines.
Chapter 5 discusses the simulation test and results for single phase and three phase shunt APF. From these results discussions are made.
Chapter 6 consists of the conclusion on the work achieved in the project and summarizes the research undertaken. It also offers recommendations for further research.
Chapter 7 contains all the references that have been used in this project.