The discontinuous conduction mode (DCM) is usually studied in single-diode and single-inductor converters, where only one DCM exists. However, multiple DCMs can appear in multidiode and multi-inductor topologies and the methodology to identify and characterize these multiple modes is not evident. In this article, a general method to study multiple DCMs is presented. The first step of the method consists in finding out the number n, which is the number of diodes conducting current passing exclusively through inductors when the transistor turns OFF. For a given n value, 2 n possible conduction modes are expected: 1 continuous mode and 2 n − 1 DCMs. The second step is to create an n-dimensional space called "k-space." In the k-space, the converter operation describes a straight line when the load changes. This straight line called "converter trajectory" passes through different n-dimensional enclosures. Each one of these enclosures represents a different conduction mode. The third step is to determine the borders between conduction modes which are subspaces of (n − 1) dimensions. This method must be followed for both control strategies (i.e., open-and closed-loop controls). The proposed method is applied to the versatile buck-boost converter. Experimental results verify the theoretical analysis for all the identified conduction modes.
In this paper, we studied the discontinuous conduction modes (DCMs) of modified versions of the SEPIC, Ćuk, and Zeta converters. The modified versions of these converters were obtained by adding an extra diode to the classical versions of these converters; thus, we obtained converters with multiple DCMs. In the case of the SEPIC and Ćuk converters, the additional diode was added in series with the inductor placed at the input port, thus resembling the connection of a four-diode bridge rectifier at the input (where these converters work as power factor correctors in AC/DC conversion). The 2 diodes of the modified versions of these converters define 4 possible conduction modes: 1 continuous conduction mode (CCM) and 3 DCMs. In this paper, the 4 conduction modes were exhaustively studied, calculating their voltage conversion ratios and the equations of the curves that define the borders between conduction modes in both open- and closed-loop operations. The conduction modes and the straight line that describes the converter operation are represented in a plane called the “k1k2 plane”. As in the case of other characteristics exhibited by the SEPIC, Ćuk, and Zeta converters, the conduction modes, the voltage conversion ratios in each conduction mode, and the boundaries between conduction modes, coincide for the three studied converters. Finally, all theoretical predictions resulting from the analysis were verified experimentally through a reconfigurable converter prototype, working as both modified SEPIC and modified Ćuk converters.
Complex control structures are required for the operation of photovoltaic electrical energy systems. In this paper, a general review of the controllers used for photovoltaic systems is presented. This review is based on the most recent papers presented in the literature. The control architectures considered are complex hybrid systems that combine classical and modern techniques, such as artificial intelligence and statistical models. The main contribution of this paper is the synthesis of a generalized control structure and the identification of the latest trends. The main findings are summarized in the development of increasingly robust controllers for operation with improved efficiency, power quality, stability, safety, and economics.
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