Abstract— Power quality is becoming a major concern for many electrical users. The high power non linear loads (such as adjustable speed drives, arc furnace, static power converter etc) and low power loads (such as computer, fax machine etc) produce voltage fluctuations, harmonic currents and an inequality in network system which results into low power factor operation of the power system. The devices commonly used in industrial, commercial and residential applications need to go through rectification for their proper functioning and operation. Due to the increasing demand of these devices, the line current harmonics create a major problem by degrading the power factor of the system thus affecting the performance of the devices. Hence there is a need to reduce the input line current harmonics so as to improve the power factor of the system. This has led to designing of Power Factor Correction circuits. Power Factor Correction (PFC) involves two techniques, Active PFC and Passive PFC. An active power factor circuit using Boost Converter is used for improving the power factor. This thesis work analyzes the procedural approach and benefits of applying Bridgeless Boost Topology for improving the power factor over Boost Converter Topology. A traditional design methodology Boost Converter Topology is initially analyzed and compared with the Bridgeless Boost topology and the overall Power Factor (PF) can be improved to the expectation. Method of re-shaping the input current waveform to be similar pattern as the sinusoidal input voltage is done by the Boost converter and the related controls that act as a Power Factor Correction (PFC) circuit. Higher efficiency can be achieved by using the Bridgeless Boost Topology. In this paper simulation of Boost Converter topology and Bridgeless PFC boost Converter is presented. Performance comparisons between the conventional PFC boost Converter and the Bridgeless PFC Boost Converter is done. Keywords— THD, Power Factor Correction (PFC), PFC Boost Converter, Bridgeless PFC Boost Converter. I. INTRODUCTION In this paper the power factor correction of a system using Bridgeless Boost Topology.
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Power Factor is an important performance parameter of a system and improving power factor is very much essential for the better and economical performance of the system. If the power factor of a system at a given power requirement is poor, then large value of Volt-Amperes or large amount of current is required by the system which is drawn from the supply. Hence it is seen that various measures are taken to improve the power factor of a system. The use and study of a Boost Converter Topology for the Power Factor Correction is described. It also describes the use and study of Bridgeless Boost Topology for power Factor Correction. The basic purpose of a Power Factor Correction circuit is to make the line current follow the waveform of the line voltage so that the input to the power supply becomes purely resistive and hence to improve the power factor. Bridgeless Boost Topology is used in the Power Factor Correction circuit to improve the power factor. The paper shows the study and analysis of power factor of a system by doing simulations on MATLAB (R2009a) Software using full wave rectifier in the beginning. After studying and analyzing the input current and voltage waveforms and the power factor of the system using Rectifier circuit, the Boost Converter is introduced in the circuit and then analyzed its effect in improving the power factor of the system. Then Bridgeless Boost Topology is implemented which gives better results and improved power factor. II. POWER FACTOR Power factor can be defined as the ratio of active or real power to the apparent power. Power Factor = Real Power ⁄ Apparent Power (1) (2) Where Root Mean Square Voltage of Load Root Mean Square Current of Load If the load is purely resistive, then the real power will be same as Vrms*Irms. Hence, the power factor will be unity. And if the load is not purely resistive, the power factor will be below unity. Assuming an ideal sinusoidal input voltage source, the power factor can be expressed as the product of two factors, the distortion factor and the displacement factor, as given
Where the fundamental component of the line is current, is the total line current and is the phase shift of the current fundamental relative to the sinusoidal line voltage. The distortion factor is close to unity, even for waveforms with noticeable distortion; therefore, it is not a very convenient measure of distortion for practical use. The distortion factor is uniquely related to another figure of merit; the total harmonic distortion (THD). (6) (7) Power factor correction circuits are developed so that the power factor is improved which means it tries to make the input to a power supply behave like purely resistive. This is done by trying to make the input current in response to the input voltage, so that a constant ratio is maintained between the voltage and current. This would ensure the input to be resistive in nature and thus, the power factor to be 1.0 or unity. When the ratio between voltage and current is not constant i.e. the load is not purely resistive, or the input to the power supply is not resistive, then the input will contain phase displacement and harmonic distortion, both of which will severely affect and degrade the power factor [1,2]. (8) (9) III. EFFECTS OF HARMONICS The non-linear loads result in production of harmonic currents in the power system. These harmonics in turn result in various undesirable effects on both the distribution network and consumers. In transformers, shunt capacitors, power cables, AC machines and switchgear, they cause extra losses and overheating leading to their premature aging and failure. In a three-phase four-wire system, excessive current flows in the neutral conductor. This is due to odd triple-n current harmonics (triple-n: 3rd, 9th, 15th, etc.) and eventually they cause tripping of the protective relay due to overheating of the neutral conductor. By interaction with the system components resonances take place in the power system. This causes huge increase in amplitude of peak voltages and RMS currents [3]. The line voltage that gets distorted due to the harmonics may affect other consumers connected to the electricity distribution network. The power factor gets reduced. Due to this the active power that is available is less than the apparent power supplied. Other effects include – telephone interference, extra audio noise, cogging and crawling of induction motors, errors observed in metering equipments. IV. STANDARS FOR LINE CURRENT HARMONICS For limiting the line current harmonics in the current waveform standards are set for regulating them. One such standard was IEC 555-2, which was published by the International Electro-technical Committee in 1982. In 1987, European Committee for Electro-Technical Standardization – CENELEC, adopted this as an European Standard EN 60555-2. Then standard IEC 555-2 has been replaced by standard IEC 1000-3-2 in 1995. The same has been adopted as an European standard EN 61000-3-2 by CENELEC. Hence, these limitations are kept in mind while designing any instrument. So that there is no violation and the negative effects of harmonics are not highly magnified [4]. V. CONVERTER TOPOLOGY Boost Converter It is a type of power converter in which the DC voltage obtained at the output stage is greater than that given at the input. It can be considered as a kind of switching-mode power supply (SMPS). The inductor has this peculiar property to resist any change of current in them and that serves as the main principle which drives a boost converter. The inductor acts like a load (like resistor) when it is being charged and acts as a source of energy (like battery) when it is discharged Fig.1: Boost converter The input current and the inductor current are the same. Hence as one can see clearly that current in a boost converter is continuous type and hence the design of input filter is somewhat relaxed or it is of lower value. Among different PFC topologies, the single switch conventional PFC is the most widely used topology because of its simplicity. The circuit topology is shown in Figure 2. A Conventional Boost PFC is considered to be the best choice for designing the power stage of the active power factor corrector. The boost converter can operate in two
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