724 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 14, NO. 4, JULY 1999 A Fuzzy-Controlled Active Front-End Rectiﬁer with Current Harmonic Filtering Characteristics and Minimum Sensing Variables Juan W. Dixon, Senior Member, IEEE, Jos´ e M. Contardo, and Luis A. Mor´ an, Senior Member, IEEE Abstract— A control strategy which allows conventional voltage-source current-controlled (VSCC) pulsewidth modulation (PWM) rectiﬁers to work simultaneously as active power ﬁlters is presented. The proposed control strategy also allows compensating the system power factor and compensating unbalanced loads. The measurement and/or calculation of the harmonics and reactive power are not required, making the proposed control scheme very simple. The active front-end rectiﬁer acts directly on the mains line currents, forcing them to be sinusoidal and in phase with the mains voltage supply. To improve the dynamic of the system, the amplitude of the current is controlled by a fuzzy system, which adjusts the dc-link voltage of the PWM rectiﬁer. The strategy is based on connecting all the polluting loads between the PWM rectiﬁer and their input current sensors. The main advantages of this approach are the following: 1) there is no need to install a specially dedicated active power ﬁlter; 2) it also works simultaneously as power factor compensator; and 3) no special and complicated calculations are required for harmonic elimination. The viability of the proposed active front-end rectiﬁer is proved by simulation and with experimental results obtained from a 2-kVA PWM prototype. I. INTRODUCTION T RADITIONALLY, passive ﬁlters have been used to eliminate line current harmonics and to improve the load power factor. However, in practical applications these passive second-order ﬁlters present many disadvantages such as aging and tuning problems, series and parallel resonance, and the requirement to implement one ﬁlter per frequency harmonics that needs to be eliminated. In order to overcome these problems, different kinds of active power ﬁlters, based on force-commutated devices, have been researched and de- veloped [1], [2]. Particularly, shunt active power ﬁlters, using different control strategies, have been widely investigated. They have gradually been recognized as a viable solution to the problems created by high-power nonlinear loads [3], [4]. These ﬁlters operate as current sources, connected in parallel with the nonlinear load, and generate the current harmonic components required by the load. In this form the mains only needs to supply the fundamental, avoiding contamination problems along the distribution lines. However, shunt active ﬁlters present the disadvantages that are difﬁcult to implement Manuscript received July 7, 1998; revised January 27, 1999. This work was supported by Conicyt under Project Fondecyt 1 960 572. Recommended by Associate Editor, A. Kawamura. J. W. Dixon is with the Department of Electrical Engineering, Pontiﬁca Universidad Cat´ olica de Chile, Santiago, Chile. J. M. Contardo is with Hidroel´ ectrica Guardia Vieja S.A., Chile. L. A. Mor´ an is with the Universidad de Concepci´ on, Concepci´ on, Chile. Publisher Item Identiﬁer S 0885-8993(99)05560-X. in large scale, the control is complicated [5], [6], and the cost is high. To reduce those drawbacks, the solution proposed in this paper is to use a conventional four-quadrant voltage-source current-controlled (VSCC) pulsewidth modulation (PWM) rec- tiﬁer simultaneously as a shunt active power ﬁlter. This is accomplished by simply connecting all the polluting loads between this rectiﬁer and their line current sensors. This solution reduces the cost of the ﬁlter to almost zero because there is no need to install a specially dedicated power device for harmonic elimination. Besides, this approach presents the following particular characteristics: 1) the four-quadrant rectiﬁer–inverter system can operate as an active ﬁlter and as a power factor compensator simultaneously; 2) it also can operate to compensate unbalanced loads; and 3) the control block is quite simple because there is no need to evaluate and/or to sense the current waveforms of the polluting loads. II. PRINCIPLES OF OPERATION Fig. 1(a) shows the schematic of the proposed control strategy, which is being applied to a conventional VSCC PWM rectiﬁer. The control only needs to measure the dc-link voltage and the mains line currents As it can be observed, neither the polluting load current nor the rectiﬁer current need to be measured. This fact is very important because almost any current-controlled PWM rectiﬁer can be used as a shunt active power ﬁlter, without the need of additional electronic circuitry. All polluting loads (three-phase polluting loads in Fig. 1) are connected between the rectiﬁer and their current sensors. By doing that, the rectiﬁer behaves as a shunt active power ﬁlter, but without loosing its characteristics as a four-quadrant rectiﬁer. The current-controlled rectiﬁer does not detect the proximity of the nonlinear load. It simply try to keep the mains current sinusoidal because the current sensors are located at the mains side, and they follow a sinusoidal template. In this way, there is no need to sense and/or calculate, neither the polluting load current nor the ﬁlter current. In this way, the PWM converter can operate as a four-quadrant rectiﬁer, as a power factor compensator, and as an active power ﬁlter simultaneously. It can also compensate unbalanced loads. In other words, it works as a multiple-function power converter. The control strategy is conventional in the sense that the dc-link voltage of the rectiﬁer is controlled by adjusting the amplitude of the input ac currents. Due to the multiple capability of this 0885–8993/99$10.00  1999 IEEE