A comparative investigation on the use of random modulation schemes for dc/dc converters is presented. The modulation schemes under consideration include randomized pulse position modulation, randomized pulsewidth modulation (PWM), and randomized carrier-frequency modulation with fixed and variable duty cycle. The paper emphasizes the suitability and applicability of each scheme in dc/dc converters. Issues addressed include the effectiveness of randomness level on spreading the dominating frequencies that normally exist in constant-frequency PWM schemes, and the low-frequency power spectral density (PSD) of each scheme. The validity of the analyses is confirmed experimentally by using a dc/dc buck converter operating in continuous conduction mode. The PSD of the output under each scheme will be presented and compared.

A novel technique for efficiently extracting the maximum output power from a solar panel under varying meteorological conditions is presented. The methodology is based on connecting a pulse-width-modulated (PWM) dc/dc SEPIC or Cuk converter between a solar panel and a load or battery bus. The converter operates in discontinuous capacitor voltage mode whilst its input current is continuous. By modulating a small-signal sinusoidal perturbation into the duty cycle of the main switch and comparing the maximum variation in the input voltage and the voltage stress of the main switch, the maximum power point (MPP) of the panel can be located. The nominal duty cycle of the main switch in the converter is adjusted to a value, so that the input resistance of the converter is equal to the equivalent output resistance of the solar panel at the MPP. This approach ensures maximum power transfer under all conditions without using microprocessors for calculation. Detailed mathematical derivations of the MPP tracking technique are included. The tracking capability of the proposed technique has been verified experimentally with a 10-W solar panel at different insolation (incident solar radiation) levels and under large-signal insolation level changes.Index Terms-dc-dc power conversion, maximum-power-pointtracking, photovoltaic.

A rigorous mathematical analysis and a comparative study of carrier-frequency modulation (CFM) techniques for the conducted electromagnetic interference (EMI) suppression in pulsewidth-modulated converters is presented. CFM techniques dither the switching period with a small amplitude variation around the nominal value, so that the harmonic power is redistributed over the spectrum of concern. Two types of dithering signals, including the periodic and random signals, are investigated in this paper. The operational characteristics as well as the input and output power spectra of the converters with the two modulating signals are compared. In particular, their characteristics in the low-and high-frequency harmonic power redistribution will be depicted. It is shown that random CFM (RCFM) gives a more effective way to disperse the harmonics around the switching frequency than the periodic CFM (PCFM) with the same frequency deviation. However, RCFM introduces higher low-frequency harmonics than the PCFM at the converter output. Furthermore, effects of the resolution filter bandwidth in the electromagnetic compatibility analyzer on conducted EMI measurement is discussed. The validity of the analyses is confirmed experimentally by using a dc/dc buck converter operating in continuous conduction mode.

A novel technique for efficiently extracting maximum power from photovoltaic (PV) panels is presented. The power conversion stage, which is connected between a PV panel and a load or bus, is a SEPIC or Cuk converter or their derived circuits operating in discontinuous inductor-current or capacitor-voltage mode. Method of locating the maximum power point (MPP) is based on injecting a small-signal sinusoidal perturbation into the switching frequency and comparing the ac component and the average value of the panel terminal voltage. Apart from not requiring any sophisticated digital computation of the panel power, the proposed technique does not approximate the panel characteristics and can globally locate the MPP under wide insolation conditions. The tracking capability has been verified experimentally with a 10 W solar panel under a controlled experimental setup. Performances under the steady state and in the large-signal change of the insolation level will be given.