Active Power Filter

Like any generator of electric power, a network of power provides energy to the apparatuses users by the intermediary of the tensions which it maintains on their terminals.It appears obvious that the quality of this energy depends on that of the tension at the point of delivery. This tension generally undergoes many disturbances of two distinct origins:-Disturbances of tension caused by the passage, in the electrical supply networks, of the interference currents like the harmonic, unbalanced and reactive currents,-Disturbances of tension caused by disturbing tensions like the harmonic and unbalanced tensions and the hollows of tension.In an electrical network, unbalanced and harmonic currents generated by nonlinear and unbalanced loads can cause harmonics and unbalanced voltage. These voltage perturbations along with voltage sag can strongly degrade customer power quality.Nowadays, the active filters such as shunt, series and combined shunt-series are studied as a flexible solution to compensate all current and voltage perturbations.This paper presents designing the active power filter. This parallel type active power filter is used to improve power factor of non-linear load to be nearly 1.The principle is that the active power filter would support reactive power and harmonics power that load consumes, then the power supply would deliver only average powerThe filter consists of a capacitor, an inductor and four power switches. The capacitor is a source where energy is stored in for balancing power. The inductor is used to decrease rate of current change. And the power switches are used to control the direction of power flow. The power switches is able to control the direction of power flow as long as the capacitor voltage is kept higher than the system voltage. And besides switching could control the system current to be sine wave that is in-phase to system voltage. The command that is used to define the amplitude of the reference current, is generated by comparing the capacitor voltage with the reference voltage, this is done to keep the capacitor voltage constant.Within the framework of report of thesis for the obtainment of Master degree it has carried out a didactic system of compensation of harmonics and reactive power. The prototype was elaborated in automatic dept, control engineering laboratories (in central south university).With the technical assistance from members of the laboratory and under the direction of professor "An Luo", the adopted solutions make it possible to as well consider the use of this didactic system in electric engineering (within the framework of the tests of systems) as in TP of physics applied.The active compensator was built around an inverter "didactic", whose characteristics (current - tension) of this product make it possible to use loads, supplied with network L.T industrialist 400 V, of significant power of the field of electrical engineering (limited to 3 KW for tests laboratory).To meet a teaching aim, we chose to carry out the charts of order into analogical. So student's electro technologists easily can analyzer the structure of the loops of control and to check the signals with an oscilloscope. The order allows operation in compensation of reactive power or harmonics but also in rectification PWM, sinusoidal absorption.The compensator can be associated any balanced three-phase load, nonlinear. In Present thesis comprises:1. The study of the compensation activates by inverter PWM;2. The dimensioning of elements of power and the control loops;3. The study functional and structural of the checking circuits.