K.K. Tse

A novel maximum power point tracking technique for solar panels using a SEPIC or Cuk converter

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.

A novel maximum power point tracker for PV panels using switching frequency modulation

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. A 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 are given.

Analysis and spectral characteristics of a spread-spectrum technique for conducted EMI suppression

Frequency modulation (FM) and random switching methods have been used for reducing conducted electromagnetic interference (EMI) in power converters. Limited theoretical studies and comparisons of these schemes, however, are available. In this paper, a detailed analysis and the spectral characteristics of a random carrier-frequency (RCF) technique for suppressing conducted EMI in an offline switched-mode power supply are presented. The analysis provides a theoretical platform for studying the characteristics of this random switching scheme. The level of randomness is defined for the RCF scheme and varied in the converter example so that the effects on the power spectra can be demonstrated. Theoretical predictions of the spectral characteristics of this scheme are confirmed with measurements. The RCF scheme has been compared with the standard constant-frequency pulsewidth modulation (PWM) scheme and the FM scheme. Comparisons of their spectral performance show that the RCF scheme has better conducted EMI suppression than the FM and standard PWM schemes.

Reduction of power converter EMI emission using soft-switching technique

Measurements of conducted and radiated electromagnetic interference (EMI) emission from hard-switched and soft-switched buck, boost, and flyback converters of similar power ratings are presented. Results indicate that EMI emission can be substantially reduced by using a soft-switching technique in power converters. Thus, the soft-switching technique provides a practical and useful solution to reduce EMI emission from switched-mode power circuits. A comparison of EMI emission on the three classes of converters is also included. The flyback converter is found to be the least EMC friendly among the converters tested.

A comparative study of maximum-power-point trackers for photovoltaic panels using switching-frequency modulation scheme

A comparative study of the maximum power point trackers using a switching-frequency modulation scheme (SFMS) for photovoltaic panels is presented. Some commonly used dc/dc converters, which are applied for the power conversion stage of those trackers, will be examined. Method of locating the maximum power point (MPP) is based on injecting a small-signal sinusoidal perturbation into the switching frequency of the converter and comparing the ac component and the average value of the panels terminal voltage. Apart from not requiring sophisticated computation of the panel power, this SFMS does not approximate the panel characteristics and can globally locate the MPP under wide insolation conditions. Tracking capability of the converters under investigation will be compared, using a 10-W solar panel with a controlled experimental setup. Theoretical predictions will be verified with experimental results. Operating characteristics at steady state and in large-signal change of the insolation (incident solar radiation) level will be studied.

A comparative investigation on the use of random modulation schemes for DC/DC converters

A comparative investigation on the use of random modulation schemes for DC/DC power 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 power 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 the continuous conduction mode. The PSD of the output under each scheme is presented and compared.

An evaluation of the spectral characteristics of switching converters with chaotic carrier-frequency modulation

This paper presents an evaluation of the spectral characteristics of switching converters with a chaotic carrier-frequency modulation scheme (CCFMS). By incorporating a Chuas circuit (CC) into the pulsewidth modulator for driving the switches, three modulation schemes, including the standard pulsewidth modulation scheme, periodic carrier-frequency modulation scheme, and CCFMS, can be realized with the CC in equilibrium, limit cycle, and chaos, respectively. The property of frequency spreading in CCFMS is studied by using a statistical analysis method. The developed model is applied to formulate the power spectral densities of the input current and the output voltage of the three basic DC/DC converters under CCFMS. Theoretical predictions are verified with experimental measurements.

A novel maximum power point tracking technique for PV panels

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 DC/DC converter operating in discontinuous inductor-current or capacitor-voltage mode. The 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 different insolation levels and a large insolation level change will be studied.

A comparative study of using random switching schemes for DC/DC converters

This paper addresses a comparative investigation on the use of random modulation schemes for DC/DC power converters. The modulation schemes under investigation include randomized pulse position modulation, randomized pulse width modulation and randomized carrier frequency modulation with fixed and variable duty cycle. The study emphasizes the suitability and applicability of each scheme in DC/DC power converters, the randomness level on the effectiveness of spreading the dominating frequencies in constant frequency pulse width modulation scheme, and the low-frequency power spectral density (PSD) of each scheme. Validity of analyzes is confirmed experimentally by using a DC/DC buck converter, where the PSD of the output for each scheme is presented.

Quadratic state-space modeling technique for analysis and simulation of power electronic converters

This paper presents a quadratic state-space modeling technique for analysis of power electronic converters. The methodology is based on using a least-square-error fitting to derive a quadratic state-space representation for each topology, together with automatic determination of switching topology. The algorithm integrates the advantages of calculating topology responses at the circuit level and determining switching instants at the device level. Several key features of the new model that lead to significant improvements in computational efficiency include: (1) its simple quadratic polynomial representation for the state-transition matrix in solving the differential equations describing each topology; (2) its direct and single-step calculation of the switching instants; and (3) its generality in determining valid topology without a prior understanding of the switching relationships. Several examples illustrating the generality and simulation speed of the proposed approach are presented. The computational efficiency of the new approach is demonstrated by comparing its simulation time with commercial software using the stepwise integration algorithm. The accuracy is verified with the exact method and available literature.