Chapter IIB-1 - System Electronics

Abstract

This chapter describes the techniques of direct current (DC) to DC conversion. For electronic power conversion it is essential that high efficiency be maintained, both to avoid wasting power and to avoid excessive heat dissipation in the electronic components. For this reason all practical power conversion circuits are built around energy storage components (inductors and capacitors) and power switches. The power switches used depend on the level of power to be converted or controlled. Metal oxide field effect transistors are usually used at relatively low power or insulated gate bipolar transistors at higher powers. At one time the use of thyristors was common, but these have been generally superseded, except at the very highest power levels. There are three basic circuit topologies for DC-to-DC converters: the buck or forward converter, the boost converter, and the buck boost, or fly-back converter. The key components of the buck converter are the inductor, the switch, and the diode. The boost converter in continuous conduction draws a continuous source current, but the load current will be discontinuous. This continuous source current may be advantageous for PV applications as it reduces the filtering required between the PV array and the converter. The buck-boost converter has the feature that the voltage may be increased or decreased, depending on the switching duty ratio. The output voltage is however of opposite sign to the input voltage.