DC/DC converters, in some types of applications such as portable equipments, can requiremore space than it is actually available. The inductor is typically the most bulky element andthe possibility to reduce its size can save up to 50% of the converter volume and area ,thus increasing the power density. This reduction, however, comes with nonlinear effectscaused by the saturation of the ferromagnetic core. An appropriate modelling of the inductorand of the converter circuit is needed for guaranteeing a good output power quality (Fig. 1).A Boost converter with an inductor in the partially saturated roll-off operating zone wasdesigned and realized to study the behaviour of DC/DC converters with nonlinear inductors(Fig. 2). The main components of the circuit are listed in Table I. An innovative polynomialmodel of the inductor  has been used for the circuit simulations. The Boost circuit model isderived from . The converter control system has been implemented on a Nucleo64-STM32F401RE microcontroller; this system manages the startup of the converter, regulatesthe output voltage and implements a control of the inductor current via a current loop (Fig. 3).An example of the system stability under a 10% step variation of the load is shown in Fig. 4.For the experimental measurement a test rig has been set up, the elements of which are listedin Table II. Initially, the converter is operated at high frequency (f=15 kHz) with low currentripple. By changing the average current, the inductor is characterized in its linear and partialsaturation zones. Then, the current ripple is increased to 2A by decreasing the switchingfrequency to 2 kHz, in order to simulate an equivalent reduction of the inductor value (volumereduction); in this case, the cusp-shaped current waveform, typical of saturated inductors, canbe noted (Fig. 5). Finally the converter has been forced to work in discontinuous conductionmode (DCM) by increasing the load resistance; even in this case the current control systemguarantees the output voltage regulation and the system stability (Fig.6).In conclusion, in this work the reduction of the inductor volume has been considered togetherwith its two main consequences: the non-linear behaviour for heavy loads and thediscontinuous conduction mode (DCM) for light loads. In both cases, it has been shown thatthe converter is able to handle partial saturation and to operate correctly in DCM thanks to thecurrent control with consequent beneficial effects on power density.
|Numero di pagine||2|
|Stato di pubblicazione||Published - 2017|