chap16 - 16 Power and Harmonics in Nonsinusoidal Systems...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
16 Power and Harmonics in Nonsinusoidal Systems Rectification used to be a much simpler topic. A textbook could cover the topic simply by discussing the various circuits, such as the peak-detection and inductor-input rectifiers, the phase-controlled bridge, polyphase transformer connections, and perhaps multiplier circuits. But recently, rectifiers have become much more sophisticated, and are now systems rather than mere circuits. They often include pulse-width modulated converters such as the boost converter, with control systems that regulate the ac input current waveform. So modern rectifier technology now incorporates many of the dc–dc converter fundamentals. The reason for this is the undesirable ac line current harmonics, and low power factors, of con- ventional peak-detection and phase-controlled rectifiers. The adverse effects of power system harmonics are well recognized. These effects include: unsafe neutral current magnitudes in three-phase systems, heating and reduction of life in transformers and induction motors, degradation of system voltage wave- forms, unsafe currents in power-factor-correction capacitors, and malfunctioning of certain power sys- tem protection elements. In a real sense, conventional rectifiers are harmonic polluters of the ac power distribution system. With the widespread deployment of electronic equipment in our society, rectifier harmonics have become a significant and measurable problem. Thus there is a need for high-quality rec- tifiers, which operate with high power factor, high efficiency, and reduced generation of harmonics. Sev- eral international standards now exist that specifically limit the magnitudes of harmonic currents, for both high-power equipment such as industrial motor drives, and low-power equipment such as electronic ballasts for fluorescent lamps and power supplies for office equipment. This chapter treats the flow of energy in power systems containing nonsinusoidal waveforms. Average power, rms values, and power factor are expressed in terms of the Fourier series of the voltage and current waveforms. Harmonic currents in three-phase systems are discussed, and present-day stan- dards are listed. The following chapters treat harmonics and harmonic mitigation in conventional line- commutated rectifiers, high-quality rectifier circuits and their models, and control of high-quality rectifi- ers.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
590 Power and Harmonics in Nonsinusoidal Systems 16.1 AVERAGE POWER Let us consider the transmission of energy from a source to a load, through a given surface as in Fig. 16.1. In the network of Fig. 16.1, the voltage waveform v ( t ) (not necessarily sinusoidal) is given by the source, and the current waveform is determined by the response of the load. In the more general case in which the source output impedance is significant, then v ( t ) and i ( t ) both depend on the characteristics of the source and load. Balanced three-phase systems may be treated in the same manner, on a per-phase basis, using a line current and line-to-neutral voltage.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/17/2010 for the course EL 5673 taught by Professor Dariuszczarkowski during the Spring '09 term at NYU Poly.

Page1 / 19

chap16 - 16 Power and Harmonics in Nonsinusoidal Systems...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online