Compensation active des perturbations dans un reseau basse tension

Abstract

he present work deals with the study of the active compensations of different disturbances in low voltage power system. Recently several methods for limitation and elimination of disturbances and harmonic pollution in power system have been widely investigated. This problem rapidly intensifies with the increasing amount of electronic equipment (computer, radio, TV sets, telecommunication etc.) and power electronics systems, mainly in industrial equipment. This equipment, a nonlinear load, is a source of current harmonics, which produces increase of reactive power and power losses in transmission lines. The harmonics also cause electromagnetic interference and, sometimes, dangerous resonances. They have negative on the control and automatic equipment, protection systems, and other electrical sensitive loads, resulting in reduced reliability and availability. Moreover, nonlinear loads and non-sinusoidal currents produce non-sinusoidal voltages drops across the network impedances, so that nonsinusoidal voltages appear at several points of the mail line, especially in the PCC (Point of Common Connection), it brings out a lot of problems in the power system, mainly overheating of line, transformers and generators due to the iron losses. In this work we present the active compensations for the whole above mentioned problems. To compensate for current disturbances, we use a Shunt Active Power Filter, which consists of an element of energy storage (DC-link), a VSI and an outer passive filter. The control algorithm used is the Instantaneous Reactive Power called the pq theory, we have discussed the use of this strategy, its drawbacks. We proposed a PLL system to allow to this strategy to work under unbalanced power system voltage or under distorted voltages and even in the case of unbalanced and distorted power system voltages. To compensate for Voltage sags, swells and partial or total collapse of one or more phases we use a Series Active Power Filter. In this work we propose a compensation technique that uses a Series Active Power Filter to eliminate the presence of voltage unbalance in a threephase a power supply, to eliminate the drop voltage in the line produced by the harmonic currents generated by nonlinear loads or in other word to eliminate the propagation of currents harmonics to travel towards the source of the power supply, finally to regulate the positive sequence voltage to a nominal value. In the end of this work we present a combined system which contains the tow Active Power Filters above mentioned coupled via a DC-link, this system is a promised solution; we called this type a Unified Power Quality Conditioner