This paper presents a three-phase four-wire Shunt Active Filter that compensates power quality problems and can also interface renewable energy sources with the electric grid. The inverter stage of the active filter is based in a two-level four-leg inverter and its control is based in the Theory of Instantaneous Reactive Power (p-q Theory). The filter is capable of compensating power factor, unbalance, and current harmonics. Additionally it can also make the interface between renewable energy sources and the electrical system, injecting balanced practically sinusoidal currents (with low THD).

Abstract. This paper presents a single-phase shunt active filter designed to minimize problems related to power quality in electrical systems. The power stage of the active filter is based on a two-leg full-bridge inverter, with a single capacitor in the dc side, and a filter inductor in the ac side. The control system is based on the instantaneous power theory in the α-β-0 reference frame (pq-theory), derived to be applied in singlephase systems. In essence, the shunt active filter is designed to drain, from the electric grid, harmonic and reactive components of the load currents, such that the system current will become, basically, a sinusoidal waveform, with low harmonic distortion, and in phase with the system voltage. Simulation results of the shunt active filter operating with three different loads are presented in order to verify its performance.

This paper describes a combined operation involving a series active filter and shunt passive filters for three-phase three-wire systems. The series active filter is able to minimize Power Quality problems like unbalances, harmonics and flicker observed at the system voltages. Another task for the series active filter is to damp possible resonances involving the passive filters and the system impedance. The shunt passive filters are designed to drain harmonic current-components generated by the load. The control strategy of the series active conditioner is based on the instantaneous power theory on α-β-0 reference frame, together with a robust synchronizing circuit PLL (Phase-Locked-Loop). A dc-link voltage controller, applied to the series conditioner, is also introduced due to the fact that there is only a single capacitor at the inverter dc-side. Simulation results on PSCAD®/EMTDC™ are presented in order to verify the performance involving a combined operation of passive and active filters.

This paper presents experimental results obtained with a developed single-phase shunt active power filter laboratory prototype operating with different switching techniques. This active filter can compensate harmonic currents and power factor in single-phase electric installations. Its power circuit is based on a two-leg IGBT inverter, with a single capacitor in the dc side, and an inductor in the ac side. Its control system is based on a simple stratagem that enables the use of the traditional Theory of Instantaneous Reactive Power (p-q Theory), originally developed to three-phase power systems, in single-phase systems. The experimental results are obtained for the active filter operating with two different switching techniques: Periodic Sampling (with variable switching frequency) and Pulse Width Modulation (with constant switching frequency) for two different frequencies (8 kHz and 16 kHz). Three different types of loads are used: linear RL load, rectifier with RL load, and rectifier with RC load.

This paper describes different types of parallel association of Shunt Active Power Filters, presents computer simulation models developed in PSCAD®/EMTDC™, and shows simulated results for each case. The control system used in the active filters is based on the Instantaneous Reactive Power Theory (p-q Theory). The active filters use periodic sampling as switching technique. Two types of parallel associations are presented: two active filters in different parallel feeders; and both active filters connected in parallel at the same point of the electric installation. The paper also proposes a control strategy to solve an inherent operation problem that occurs in the second type of parallel association.