The new adaptive hysteresis band current controller changes the hysteresis bandwidth according to the modulation frequency, the supply voltage, the DC capacitor voltage and the slope of the current wave i / sub c // sup * / reference compensator. The hysteresis band current controller determines the active power filter (APF) switching signals, and the algorithm based on an extension of the synchronous reference frame theory (dq-0) is used to determine the signals of current reference.
The use of modern electronic equipment has changed our lives and has introduced a variety of loads in power systems. This has changed the charging characteristics of the electricity supply networks, all electronic loads are "non-linear" (the current is not proportional to the applied voltage) and this is due to the way they extract the energy from the source. Non-linear loads will produce current and voltage components with higher frequencies in the power line. These higher frequencies of current and voltage components are known as power harmonics. Although a single low power electronic apparatus, in which a single phase diode rectifier with a DC link capacitor is used as a utility interface, produces an insignificant amount of harmonic current. Three-phase diodes or rectifiers for thyristors and cycloconverters for industrial applications also generate a large amount of harmonic current. Distortion of voltage or harmonics resulting from current harmonics produced by electronic power equipment has become a serious problem that must be solved in many countries. "Harmonics are currents and voltages which are continuous multiples of the fundamental frequency of 50 Hz, such as 100 Hz (2nd harmonic) and 250 Hz (5th harmonic)". The most commonly used non-linear loads are the switched-mode power systems found on personal computers. Microwave ovens, laser printers, medical instrumentation systems, stereos, televisions, adjustable speed pulses, and electronic lighting are also examples of equipments using switch mode power supplies. Other types of nonlinear loads include rectifiers, controlled and uncontrolled, and phase angle controlled power supplies.