The Discontinuous Conduction Mode Sepic and ´ Cuk Power

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SIMONETTI et al.: SEPIC AND ĆUK POWER FACTOR PREREGULATORS 635 (a) (b) Fig. 8. Influence of gI value. (a) Input current using gI a QXW "F. (b) gI capacitor voltage using gI aHXI"F. Also, the small-signal model was tested through simulation. From (29), it is found that (43) Considering a resistive load, and having mF, the transfer function is (44) Fig. 9(a) shows full-circuit simulation and small-signal model results for a 20-V increase in the input voltage ( ). For a constant power load, the transfer function is given by (45) Fig. 9(b) shows open-loop simulation and model results for a change of 10% in the duty cycle ( ). The estimated small-signal model results and full-circuit simulation results are in good agreement. Simulation results have shown the validity of the design approach and small-signal model presented. (a) (b) Fig. 9. Open-loop dynamic simulation results. (a) Input voltage increased by 20 V, resistive load. (b) Duty-cycle increased by 0.03, constant power load. IV. EXPERIMENTAL RESULTS The following single-phase Sepic DCM–PFP was implemented: V; kHz; W; t V; Using the equations presented in this paper, the following is obtained: Authorized licensed use limited to: ELETTRONICA E INFORMATICA PADOVA. Downloaded on April 12, 2009 at 16:08 from IEEE Xplore. Restrictions apply. mH H F (46)
636 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 44, NO. 5, OCTOBER 1997 (a) (b) (c) (d) Fig. 10. Experimental results. (a) Input voltage and current (filtered). (b) Inductor currents. (c) Output voltage. (d) Dynamic response for a load change. The control-to-output transfer function ( F) is (47) The feedback loop of a PFP must be slow (crossover frequency below one-third of the line frequency) to avoid excessive second-harmonic injection from the output voltage into the input current (resulting in third-order harmonic current) [1]. The system is stable if the open-loop transfer function crosses 0 dB with 20 dB slope. Taking these points into account, an output voltage feedback loop was implemented, yielding the following open-loop transfer function: (48) The zero crossover frequency is about 5 Hz with 20 dB slope, and the gain at 100 Hz is close to 0.01. Fig. 10(a) shows the converter input voltage and current. It can be observed that the current actually follows the input voltage. Fig. 10(b) shows and inductor currents for a few switching periods, whereas Fig. 10(c) shows the output voltage. The dynamic response of the PFP for a 100–50 W load change and vice versa can be seen in Fig. 10(d). Experimental results confirm the analysis carried out in this paper. V. CONCLUSIONS Sepic and Ćuk converters working as PFP in DCM are perfect preregulators. The input current naturally follows the input voltage, and theoretical power factor is one. The operation analysis for each stage leads to the equations for correctly designing the converter. The ripple present in the input current is limited by design, choosing an adequate value for the input inductor ( ). A correct choice of the intermediate capacitor is fundamental in obtaining a highquality input current. The static and dynamic simulation results, as well as the experimental results, have confirmed the validity of the analysis and design approaches presented here. REFERENCES [1] L. H. Dixon, “High power factor preregulators for off-line power supplies,” in Unitrode Power Supply Design Seminar Manual SEM600, Unitrode Corp., Waltham, MA, pp. 6.1–6.16, 1988. [2] I. Barbi and S. A. O. Silva, “Sinusoidal line current rectification at unity power factor with boost quasiresonant converters,” in Proc. IEEE APEC, 1990, pp. 553–562. [3] C. Zhov, R. B. Ridley, and F. C. Lee, “Design and analysis of a hysteretic boost power factor correction circuit,” in Proc. IEEE PESC, 1990, pp. 800–807. [4] J. Sebastián, J. Uceda, J. A. Cobos, J. Arau, and F. Aldana, “Improving power factor correction in distributed power supply systems using PWM and ZCS-QR Sepic topologies,” in Proc. IEEE PESC, 1991, pp. 780–791. Authorized licensed use limited to: ELETTRONICA E INFORMATICA PADOVA. Downloaded on April 12, 2009 at 16:08 from IEEE Xplore. Restrictions apply.
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The Discontinuous Conduction Mode Sepic and ´ Cuk Power

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