Active Power Filters for Harmonic Elimination and Power Quality Improvement

Abstract

The explosive growth in consumer electronics and domestic appliances has generated a major concern in the electricity supply industry, (Bollen, 1999). Due to its interface circuit (a diode bridge, followed by a large DC capacitor), these appliances draw current only near the peak of the mains voltage. Like this circuit other power electronics based applications draw non-sinusoidal currents, despite the applied voltage being sinusoidal. Due to the non-ideal characteristics of the voltage source, harmonic currents create voltage distortion. Non-linear loads such as rectifiers, cycloconverters, variable speed drives and arc furnaces, large decaying DC components, asymmetrical loads and other electrical equipment can cause high disturbances in the power supply system, (Bollen, 1999). The harmonics generated by the most common non-linear loads have the following properties: • lower order harmonics tend to dominate in amplitude; • if the waveform has half-wave symmetry there are no even harmonics; • harmonic emissions from a large number of non-linear loads of the same type will be added. The major problems caused by the mains harmonic currents are those associated with the harmonic currents themselves, and those caused by the voltage waveform distortion resulting from the harmonic currents flowing in the supply source impedance. This distortion of the voltage waveform can cause, e.g. serious effects in direct on-line induction motors, ranging from a minor increase in internal temperature through excessive noise and vibration to actual damage; electronic power supplies may fail to operate adequately; increased earth leakage current through EMI filter capacitors due to their lower reactance at the harmonic frequencies. To minimize these effects in electricity distribution systems (non-sinusoidal voltages, harmonic currents, unbalanced conditions, power de-rating, etc) different types of compensators have been proposed to increase the electric system quality, (Bollen, 1999, Hingorani & Gyugyi, 1999). One of those compensators is the active power filter (APF), (Akagi et al., 1984). This Chapter is organized as follows: in Section 2, it is presented a brief review of power quality and harmonic emission standards, while Section 3 addresses main active filter