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A control algorithm for a three-phase hybrid power filter is proposed. It is constituted by a series active filter and a passive filter connected in parallel with the load. The control strategy is based on the vectorial theory dual formulation of instantaneous reactive power, so that the voltage waveform injected by the active filter is able to compensate the reactive power and the load current harmonics and to balance asymmetrical loads. The proposed algorithm also improves the behavior of the passive filter. Simulations have been carried out on the MATLAB-Simulink platform with different loads and with variation in the source impedance. This analysis allowed an experimental prototype to be developed. Experimental and simulation results are presented.Index Terms-Active power filters, harmonics, hybrid filters, instantaneous reactive power, power quality.

A control algorithm is proposed for a three-phase hybrid power filter constituted by a series active filter and a shunt passive filter. The control strategy is based on the dual formulation of the compensation system principles. It is applied by considering a balanced and resistive load as ideal load, so that the voltage waveform injected by the active filter is able to compensate the reactive power, to eliminate harmonics of the load current and to balance asymmetrical loads. This strategy improves the passive filter compensation characteristics without depending on the system impedance, and avoiding the series/shunt resonance problems, since the set load-filter would present resistive behavior. An experimental prototype was developed and experimental results are presented.Index Terms-Active power filters (APFs), harmonics, hybrid filters, instantaneous reactive power, power quality.

For three-phase four-wire circuits, two compensation criteria have been established: one based on the instantaneous value concept and the other on the average value concept. Thus, according to the instantaneous value concept the non instantaneous power current is reduced, without altering the instantaneous active power. According to the average value concept, the nonactive average-current is reduced, without altering the average power. When the zero-sequence voltage component exists, both compensation types would not enable the zero-sequence (neutral) source current elimination. Then, two approaches are marked in this paper. The first one is for eliminating the non instantaneous power current or the nonactive average-current but the neutral current can still flow. The second one for eliminating the modified non instantaneous power current or the modified nonactive average-current, thus the neutral current component is compensated. According to recent recommendations in this work three-phase systems are considered as four-conductor systems. Experimental results are obtained to confirm the theoretical properties and to show the compensator performance.Index Terms-Active power-line conditioner, compensation, instantaneous power theory.

The instantaneous reactive power theory was pub-4 lished 25 years ago, in an IEEE TRANSACTIONS. Since then, it 5 has been the most used in nonlinear load compensation with active 6 power filters. Its application allows constant source power to be 7 obtained after compensation in a simple way. Moreover, some 8 researches have showed up some limitations of the theory, i.e., it 9 goes optimally with source voltage balanced and sinusoidal, but 10 not so good with source voltage unbalanced and/or nonsinusoidal, 11 since the source current obtained is not balanced and sinusoidal. 12 This paper presents a new compensation strategy in phase coordi-13 nates, equivalent to the original theory's one. Its simplicity, due 14 to the nonnecessity of coordinate mathematical transformation, 15 makes easier the modifications necessary to obtain alternative 16 compensation objectives. In this way, this paper presents those 17 modifications and derives compensation strategies that obtain al-18 ternative compensation objectives: unity power factor or balanced 19 and sinusoidal source current. Finally, compensation strategies are 20 applied to a practical power system, and the results are presented. 21 Index Terms-Active power filters (APFs), instantaneous reac-22 tive power theory, power quality.