New control method of active power filters with unity power factor based on time-domain decomposition of the load currents. Application to four-wire industrial systems

Due to the great increase of consumptions formed by non-lineal loads in their majority loads that use power electronics equipments, power quality of electric utility network has suffered a deterioration in the last years. This deterioration has supposed an increment in the reactive power required. This reactive power doesn't contribute to a net transfer of energy from the electric utility network to the load so it should be compensated. One of the most novel solutions to compensate reactive power it is to use shunt active power filters.; As previous stage for controlling active power filters, it is necessary to obtain the reference currents starting from the non-lineal load currents. Nowadays different methods exist to obtain these reference currents. They all have a poor performance from the unity power factor point of view under non-sinusoidal and unbalanced AC voltages. In the present thesis a novel method of obtaining the reference currents bases on the decomposition in the time domain of the load currents using the Park's transformation is proposed. This method presents a good performance from the unity power factor point of view under any AC voltages system. With this method, it is also possible to make the line currents perfectly sinusoidal without hardly doing modifications on this. The obtaining system of the reference currents has been applied to an active power filter that uses a VSI-PWM four-branch inverter. This uses a new current controller based on a space vector generalization using Scott's transformation that is able to decrease the relationship between DC and AC voltage of the active power filter in comparison with other methods bases on this same theory. In this way, a decrease of the inverter switching losses is produced.