![]() ![]() Since it is easier to build, tightly-coupled inductors were wound on a single core. ![]() It was shown that there was no significant difference in the control characteristics when tightly or loosely coupling the inductor windings. This can also be done for the Cuk converter. In the previous articles on the Sepic converter, coupling the two inductors on the same core removed the difficult characteristics. One way to control this variability is with additional RC damping branches, but this yields a 6th order power circuit and the analysis becomes even more complex. These moving zeros make the control of the converter extremely difficult over the full range, and the changing characteristics are a function of the parasitic damping of the circuit. However, the characteristic varied substantially in the range from 4 kHz to 8 kHz, with an extra pair of RHP zeros appearing at low line, and high-Q LHP zeros at higher input lines. Figure 2 shows the results of these measurements.įigure 2: Range of Transfer Functions for the Separate-Inductor Cuk Converterįor all input voltages, the low frequency gains of the measured transfer functions were essentially the same. The input voltage was varied from 5 V to 15 V to show the range of transfer functions for the converter. Using the AP300 frequency-response analyzer, a signal was injected into the PWM modulator for the converter, and the gain and phase measured from the input to the output of the converter. The inductors are off-the-shelf parts, each with a value of 22 µH.įigure 1: Separate Inductor Cuk Converter with Control-to-Output Measurement Setup Figure 1 shows the schematic of the Cuk converter with discrete inductors, and all component values. Rather than just presenting complex control equations, the practical measurements on the Cuk are given. ![]() Like the Sepic converter, the uncoupled Cuk converter has fourth-order transfer functions, with up to three RHP zeros, depending on the converter operating point. In this article, the same techniques will be applied to the Cuk converter operating over the same voltage ranges as the Sepic. In the three articles of this series on Sepic converter measurements, it was shown that the sometimes-unpleasant converter control characteristics could be tamed by tightly coupling the two inductors of the converter on one core. The coupled-inductor Cuk has fewer diverse transfer functions, but it is still a challenge to control over a wide range. Let’s explore the measured control characteristics of a Cuk converter with separate inductors, and with a tightly-coupled inductor. ![]()
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