Three phase rectifier

Page 1

View with images and charts Reduction of Harmonics of Input Side Currents of a Three Phase Rectifier Combining Active and Passive Filters. Chapter 1 1.1 Introduction Since most loads in modern electrical distribution systems are inductive, there is an ongoing interest in improving power factor [1]. The low power factor of inductive loads robs a system of capacity and can adversely affect voltage level. To improve input power factor of power converter, normally a power factor correction (PFC) circuit is designed and placed in front end of the converter, which in turn interfaced with the load. This power factor correction circuit may be an independent unit, by which the power supply followed, or an inseparable part of circuit incorporated into the power supply of the load. The line is a voltage source and will not be distorted if the line current is a sinusoidal one. Hence the basic idea of doing PFC is straightforward, by certain means, to force the line current to follow the waveform of the line voltage. However, there exists an unbalance of instantaneous power between the input powers of the PFC circuit, which is an alternative quantity with two times the line frequency, and its dc output power. Therefore, the operation principle of a PFC circuit is to process the input power in certain way that it stores the excessive input energy when the input power is larger than the dc output power, and releases the stored energy when the input power is less than the dc output power. To accomplish the above process, at least one energy storage element must be included in the PFC circuit. Various active and passive techniques are being carried out to meet the stander. To improve the power factor and to comply with various national and international line-harmonics regulations in lineoperated electronic equipment, an active or passive power-factor-correction/lineharmonics-reduction circuit must be added to the capacitive filtered bridge or voltagedoublers front-end rectifier. Although it is straightforward to obtain negligible distortion (i.e. less than 5%) and high power factor (more than 99%) with active circuits operating at high frequency (above 20 kHz), the additional circuitry can significantly reduce the reliability and increase the complexity, EMI, and Cost of the equipment. Passive solutions (circuits without controlled switches) offer an attractive trade-off between cost and performance: they are simple, reliable, robust, generate no EMI, and still provide compliance with the norms 1.2

Definiton

Power factor correction is simply defined as the ratio of real power to apparent power, or:

PF = Real Power / Apparent Power

Where, the real power is the average, over a cycle, of the instantaneous product of current and voltage, and the apparent power is the product of the rms value of current times the rms value of voltage. If both current and voltage are sinusoidal and in phase, the power factor is 1.0. If both are sinusoidal but not in phase, the power factor is the cosine of the phase angle. 1.3 Background


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Three phase rectifier by regan rose - Issuu