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Table of Contents
- I. INTRODUCTION............................................................................................................................ ABSTRACT........................................................................................................................................ I
- 1.1 BACKGROUND OF THE STUDY....................................................................................................
- 1.2 STATEMENT OF THE PROBLEM...................................................................................................
- 1.3 OBJECTIVES................................................................................................................................
- 1.4 SIGNIFICANCE OF THE STUDY.....................................................................................................
- 1.5 SCOPE AND LIMITATIONS...........................................................................................................
- II. TOPOLOGY RESEARCH..................................................................................................................
- 2.1 SEMI-CONDUCTORS...................................................................................................................
- 2.1.1 DIODE.....................................................................................................................................
- 2.1.2 METAL OXIDE SEMICONDUCTOR FIELD EFFECT TRANSISTOR (MOSFET)....................................
- 2.2 ENERGY STORAGE COMPONENTS.............................................................................................
- 2.2.1 CAPACITOR......................................................................................................
- 2.2.2 INDUCTORS......................................................................................................
- 2.3 RECTIFIERS...............................................................................................................................
- 2.3.1 FULL WAVE RECTIFIERS..................................................................................
- 2.3.2 HALF WAVE RECTIFIERS.................................................................................
- 2.3.3 3 PHASE RECTIFIERS........................................................................................
- 2.4 SWITCHING REGULATOR (DC-DC CONVERTER)..........................................................................
- 2.4.1 BUCK CONVERTER...........................................................................................
- 2.4.2 BOOST CONVERTER.........................................................................................
- 2.4.3 BUCK-BOOST CONVERTER..............................................................................
- 2.5 LINEAR REGULATOR.................................................................................................................
- 2.6 MICROCONTROLLER.................................................................................................................
- III. METHODOLOGY........................................................................................................................
- 3.1 DATA GATHERING....................................................................................................................
- 3.2 TOPOLOGY SELECTION.............................................................................................................
- 3.2.1 RECTIFIER........................................................................................................
- 3.2.3 SWITCHING REGULATOR..................................................................................
- 3.3 PARTS SELECTION..................................................................................................................... - 3.3.1 DIODE.............................................................................................................. - 3.3.2 CAPACITORS.................................................................................................... - 3.3.3 INDUCTOR IN BOOST CONVERTER................................................................... - 3.3.4 SEMICONDUCTOR: POWER MOSFET.............................................................. - 3.3.5 MICROCONTROLLER......................................................................................... - 3.3.6 BATTERY..........................................................................................................
- 3.4 DIGITAL CONTROL....................................................................................................................
- 3.5 DESIGN AND SIMULATION OF THE POWER CONVERTER............................................................
- 3.6 TESTING AND IMPLEMENTATION OF THE CIRCUIT....................................................................
- IV. RESULTS AND DISCUSSION........................................................................................................ - 4.1 TOPOLOGY SELECTION....................................................................................... - 4.2 PARTS SELECTION............................................................................................... - 4.3 DESIGN AND SIMULATION OF THE SYSTEM........................................................ - 4.4 TESTING AND IMPLEMENTATION OF THE CIRCUIT..............................................
- V. CONCLUSION AND RECOMMENDATION....................................................................................
- 5.1 CONCLUSION.......................................................................................................
- 5.2 RECOMMENDATION.............................................................................................
- REFERENCE....................................................................................................................................
- APPENDICES.................................................................................................................................. - forMOSFET....................................................................... Table 2. 0 - 1 Switching Table
- Table 4. 1 Rectified DC Voltage NO load.....................................................................
- Table 4.2 Rectifier with Boost Converter No Load......................................................
- Table 4.3 Boost Converter with Load..........................................................................
- Table 4.4 AC voltage and Rectified Voltage on-site....................................................
- Table 4.5 Rectified Voltages with Fixed Output...........................................................
- Table 4.6 Charging Current for the Battery.................................................................
- Table 4.7 Power Converted..........................................................................................
- Table 4.8 Energy Harnessed........................................................................................
- Figure 2.1 Semi-conductor Device List of Figures
- Figure 2.2 Forward Biased P-N Junction [6]
- Figure 2.3 Reversed Biased P-N Junction [6]
- Figure 2.4 Diode Curve [6]
- Figure 2. 5 N-P Energy Bands [6]
- Figure 2.6 Symbols and Basic construction of MOSFET[7]
- Figure 2.7 Basic MOSFET Structure and Symbol[7]
- Figure 2.8 Triode Mode/Linear Region in Depletion mode[7]
- Figure 2.9 Depletion-mode N-Channel MOSFET and circuit Symbol[7]
- Figure 2.10 Triode mode or linear region in Enhancement mode[7]
- Figure 2.11 Enhancement-mode N-Channel MOSFET and circuit Symbol[7]
- Figure 2.12 Capacitor Construction[8]
- Figure 2.13 Pure Capacitive Circuit[8]
- Figure 2.14 AC Capacitor Phasor Diagram[8]
- Figure 2.15 Capacitive Reactance against Frequency[8]
- Figure 2.16 Inductor Symbols[8]
- Figure 2.17 Inductor Coil[8]
- Figure 2.18 Current and Voltage in an Inductor[8]
- Figure 2.19 Pure Inductive Circuit[8]
- Figure 2.20 AC Inductor Phasor Diagram[8]
- Figure 2.21 Inductive Reactance against Frequency[8]
- Figure 2.22 Power Triangle[8]
- Figure 2.23 Full Wave Rectifier Circuit[10]
- Figure 2.24 Half Wave Rectifier Circuit[11]
- Figure 2.25 3phase Rectifier Circuit[12]
- Figure 2.26 Buck Converter Circuit[14]
- Figure 2.27 Operation of Buck Converter ‘on’ Period[14]
- Figure 2.28 Operation of Buck Converter ‘off’ Period[14]
- Figure 2.29 Boost Converter Circuit[14]
- Figure 2.30 Operation of Boost Converter “on” period[14]
- Figure 2.31 Operation of Boost Converter “off” period[14]
- Figure 2.32 Buck-Boost Converter Circuit[14]
- Figure 33 Power Converter flow Diagram
- Figure 34 Rectifier Simulation
- Figure 35 Rectifier waveform
- Figure 36 Rectifier with DC-DC Converter Circuit with no load
- Figure 37 Rectifier with DC-DC Converter Circuit output waveform
- Figure 38 Current waveform of the Inductor
- Figure 39 PWM signal
- Figure 40 Rectifier and Boost Converter with load
I. INTRODUCTION
1.1 Background of the Study The world has gone dependent on fossil fuel to generate electricity. With the increase in demand of power, the supply of the energy has depleted rapidly. Hence, renewable energies have been introduced to compensate the increase in demand. Renewable energies like: Solar, Tidal, Hydro, and Wind have been a key research all over the world by engineers and scientist. Wind energy conversion system has been the fastest growing sustainable energy resource for wind all over the world. Wind energy can be harnessed by two types of wind turbine: Horizontal Axis Wind Turbine (HAWT) and Vertical Axis Wind Turbine (VAWT). Most modern wind turbine use HAWT in large scale but the problem for HAWT is that it is dependent on the wind direction while VAWT is a bidirectional wind turbine. Also wind turbine can be designed by constant speed or variable wind speed configuration. Variable speed wind turbines can produce 8% to 15% more energy output as compared to their constant speed counterparts, however, they necessitate power electronic converters to provide a fixed frequency and fixed voltage power to their loads.[1] At the present time and in the near future, generators for wind turbines will be synchronous generators, permanent magnet synchronous generators, and induction generators, including the squirrel cage type and wound rotor type. For small to medium power wind turbines, permanent magnet generators and squirrel cage induction generators are often used because of their reliability and cost advantages.[2] Induction generators, permanent magnet synchronous generators and wound field synchronous generators are currently used in various high power wind turbine. 1.2 Statement of the Problem The problem for wind energy conversion system is that wind speed is not constant throughout the day. A variable speed wind turbine configuration is used in this study consequently the generator output will be variable. Thus the energy that is harnessed by the wind turbine varies with time when wind is present or not. So, power converter
namely: Active Rectifier and Voltage Regulator is introduced in the variable wind speed configuration for VAWT.[3] 1.3 Objectives With VAWT, a bidirectional wind turbine, so the only problems that can be meet is that wind speed is not constant. Hence, the energy that can be harnessed in the wind varies with the existing wind. Thus, the power converter to be use is the active rectifier and its’ objectives are as follows: To convert generated 3 phase AC output of the generator to DC signal To have a fixed voltage output regardless of the input To store the harnessed energy to the battery 1.4 Significance of the Study Power converter is convenient for a small scale VAWT variable wind speed configuration for it eliminates the mechanical components of the system. Thus, minimizing the cost of the wind energy conversion system.[4] The power converter can convert variable frequency and variable voltage to a fixed DC voltage. As a result, the fixed DC voltage is stored in the battery to use the energy whenever the wind is not constant or variable. The importance of this study is to charge the battery with its required parameters and maximize the power output of the generator. Also, the purpose of this study is to optimize the battery and not overcharge the battery. 1.5 Scope and Limitations This study will be focused on the generated output of the permanent synchronous generator. With its parameters of 3-20 volts AC generated output; power converter will convert it to fixed 16 volts DC. Also, this study focuses only on power converter with the use of semi-conductor and microcontroller. This study is restricted only with low wind speed; hence whenever the wind turbine faces tremendous wind speed, the power converter will not convert and transmit power to the battery. Also this study is limited to a maximum of 50 watts.
2.1.1 Diode A diode is an electrical device allowing current to move through it in one direction with far greater ease than in the other. The most common kind of diode in modern circuit design is the semiconductor diode, although other diode technologies exist. [6] 2.1.1.1 Forward Biased Diode A forward-biased diode conducts current and drops a small voltage across it, leaving most of the battery voltage dropped across the load. Forward biasing the p-n junction drives holes to the junction from the p-type material and electrons to the junction from the n-type material. At the junction the electrons and holes combine so that a continuous current can be maintained. This forward-bias voltage drop exhibited by the diode is due to the action of the depletion region formed by the P-N junction under the influence of an applied voltage. If no voltage applied is across a semiconductor diode, a thin depletion region exists around the region of the P-N junction, preventing current flow.[6] To forward bias the p-n junction, the p side is made more positive, so that it is "downhill" for electron motion across the junction. An electron can move across the junction and fill a vacancy or "hole" near the junction. It can then move from vacancy to vacancy leftward toward the positive terminal, which could be described as the hole moving right. The conduction direction for electrons in the diagram is right to left, and the upward direction represents increasing electron energy. Figure 2. 2 Forward Biased P-N Junction [6]
2.1.1.2 Reversed Biased Diode The application of a reverse voltage to the p-n junction will cause a transient current to flow as both electrons and holes are pulled away from the junction. When the potential formed by the widened depletion layer equals the applied voltage, the current will cease except for the small thermal current. A reverse-biased diode prevents current from going through it, due to the expanded depletion region. In actuality, a very small amount of current can and does go through a reverse-biased diode, called the leakage current, but it can be ignored for most purposes. The ability of a diode to withstand reverse-bias voltages is limited, as it is for any insulator. If the applied reverse-bias voltage becomes too great, the diode will experience a condition known as breakdown, which is usually destructive. A diode's maximum reverse-bias voltage rating is known as the Peak Inverse Voltage, or PIV, and may be obtained from the manufacturer. Like forward voltage, the PIV rating of a diode varies with temperature, except that PIV increases with increased temperature and decreases as the diode becomes cooler -- exactly opposite that of forward voltage. Figure 2. 3 Reversed Biased P-N Junction [6] Figure 2. 4 Diode Curve [6]
MOSFETs are three terminal devices with a Gate, Drain and Source and both P- channel (PMOS) and N-channel (NMOS) MOSFETs are available. The main difference this time is that MOSFETs are available in two basic forms:
- Depletion Type – the transistor requires the Gate-Source voltage, ( VGS ) to switch the device “OFF”. The depletion mode MOSFET is equivalent to a “Normally Closed” switch.
- Enhancement Type – the transistor requires a Gate-Source voltage, ( VGS ) to switch the device “ON”. The enhancement mode MOSFET is equivalent to a “Normally Open” switch. The construction of the Metal Oxide Semiconductor FET is very different to that of the Junction FET. Both the Depletion and Enhancement type MOSFETs use an electrical field produced by a gate voltage to alter the flow of charge carriers, electrons for N- channel or holes for P-channel, through the semi-conductive drain-source channel. Figure 2. 6 Symbols and Basic construction of MOSFET[7]
The gate electrode is placed on top of a very thin insulating layer and there are a pair of small N-type regions just under the drain and source electrodes. The gate of a junction field effect transistor, JFET must be biased in such a way as to reverse-bias the PN-junction. With an insulated gate MOSFET device no such limitations apply so it is possible to bias the gate of a MOSFET in either polarity, positive (+ve) or negative (-ve). This makes the MOSFET device especially valuable as electronic switches or to make logic gates because with no bias they are normally non-conducting and this high gate input resistance means that very little or no control current is needed as MOSFETs are voltage controlled devices. Both the P-channel and the N-channel MOSFETs are available in two basic forms, the Enhancement type and the Depletion type. 2.1.2.1 Depletion- mode MOSFET The Depletion-mode MOSFET, which is less common than the enhancement types is normally switched “ON” without the application of a gate bias voltage making it a “normally-closed” device. However, a gate to source voltage ( VGS ) will switch the device “OFF”. Similar to the JFET types, for an N-channel MOSFET, a “positive” gate voltage widens the channel, increasing the flow of the drain current and decreasing the drain current as the gate voltage goes more negative. Figure 2. 7 Basic MOSFET Structure and Symbol[7]
place making it a transconductance device. This positive +ve gate voltage pushes away the holes within the channel attracting electrons towards the oxide layer and thereby increasing the thickness of the channel allowing current to flow. This is why this kind of transistor is called an enhancement mode device as the gate voltage enhances the channel. Increasing this positive gate voltage will cause the channel resistance to decrease further causing an increase in the drain current, ID through the channel. In other words, for an N-channel enhancement mode MOSFET: +VGS turns the transistor “ON”, while a zero or -VGS turns the transistor “OFF”. Then, the enhancement-mode MOSFET is equivalent to a “normally-open” switch. Enhancement- mode MOSFETs make excellent electronics switches due to their low “ON” resistance and extremely high “OFF” resistance as well as their infinitely high gate resistance. Enhancement-mode MOSFETs are used in integrated circuits to produce CMOS type Logic Gates and power switching circuits in the form of as PMOS (P- channel) and NMOS (N-channel) gates. CMOS actually stands for Complementary MOS meaning that the logic device has both PMOS and NMOS within its design. Figure 2. 10 Triode mode or linear region in Enhancement mode[7]
2.1.2.3 Working Principle of MOSFET The working principle of MOSFET depends up on the MOS capacitor. The MOS capacitor is the main part. The semiconductor surface at below the oxide layer and between the drain and source terminal can be inverted from p-type to n-type by applying a positive or negative gate voltages respectively. When we apply positive gate voltage the holes present beneath the oxide layer experience repulsive force and the holes are pushed downward with the substrate. The depletion region is populated by the bound negative charges, which are associated with the acceptor atoms. The positive voltage also attracts electrons from the n+ source and drain regions in to the channel. The electron reach channel is formed. Now, if a voltage is applied between the source and the drain, current flows freely between the source and drain gate voltage controls the electrons concentration the channel. Instead of positive if apply negative voltage a whole channel will be formed beneath the oxide layer. Now, the controlling of source to gate voltage is responsible for the conduction of current between source and the drain. If the gate voltage exceeds a given value, called the three voltages only then the conduction begins. MOSFETs have the ability to operate within three different regions:
- Cut-off Region – with VGS < Vthreshold the gate-source voltage is lower than the threshold voltage so the MOSFET transistor is switched “fully-OFF” and IDS = 0, the transistor acts as an open circuit
- Linear (Ohmic) Region – with VGS > Vthreshold and VDS > VGS the transistor is in its constant resistance region and acts like a variable resistor whose value is determined by the gate voltage, VGS
- Saturation Region – with VGS > Vthreshold the transistor is in its constant current region and is switched “fully-ON”. The current IDS = maximum as the transistor acts as a closed circuit
Energy storage is accomplished by devices or physical media that store energy to perform useful processes at a later time. A device that stores energy is sometimes called an accumulator.[8] 2.2.1 Capacitor Just like the Resistor, the Capacitor , sometimes referred to as a Condenser, is a simple passive device that is used to “store electricity”. The capacitor is a component which has the ability or “capacity” to store energy in the form of an electrical charge producing a potential difference ( Static Voltage ) across its plates, much like a small rechargeable battery. There are many different kinds of capacitors available from very small capacitor beads used in resonance circuits to large power factor correction capacitors, but they all do the same thing, they store charge. In its basic form, a Capacitor consists of two or more parallel conductive (metal) plates which are not connected or touching each other, but are electrically separated either by air or by some form of a good insulating material such as waxed paper, mica, ceramic, plastic or some form of a liquid gel as used in electrolytic capacitors. The insulating layer between capacitors plates is commonly called the Dielectric. Due to this insulating layer, DC current cannot flow through the capacitor as it blocks it allowing instead a voltage to be present across the plates in the form of an electrical charge. The conductive metal plates of a capacitor can be square, circular or rectangular, or they can be of a cylindrical or spherical shape with the general shape, size and construction of a parallel plate capacitor depending on its application and voltage rating. When used in a direct current or DC circuit, a capacitor charges up to its supply voltage but blocks the flow of current through it because the dielectric of a capacitor is non-conductive and basically an insulator. However, when a capacitor is connected to an alternating current or AC circuit, the flow of the current appears to pass straight through the capacitor with little or no resistance.
There are two types of electrical charge, positive charge in the form of Protons and negative charge in the form of Electrons. When a DC voltage is placed across a capacitor, the positive (+ve) charge quickly accumulates on one plate while a corresponding negative (-ve) charge accumulates on the other plate. For every particle of +ve charge that arrives at one plate a charge of the same sign will depart from the - ve plate. Then the plates remain charge neutral and a potential difference due to this charge is established between the two plates. Once the capacitor reaches its steady state condition an electrical current is unable to flow through the capacitor itself and around the circuit due to the insulating properties of the dielectric used to separate the plates. The flow of electrons onto the plates is known as the capacitors Charging Current which continues to flow until the voltage across both plates (and hence the capacitor) is equal to the applied voltage Vc. At this point the capacitor is said to be “fully charged” with electrons. The strength or rate of this charging current is at its maximum value when the plates are fully discharged (initial condition) and slowly reduces in value to zero as the plates charge up to a potential difference across the capacitors plates equal to the source voltage. The parallel plate capacitor is the simplest form of capacitor. It can be constructed using two metal or metallized foil plates at a distance parallel to each other, with its capacitance value in Farads, being fixed by the surface area of the conductive plates and the distance of separation Figure 2. 12 Capacitor Construction[8]
