Non-Linear Inductors Characterization in Real Operating Conditions for Power Density Optimization in SMPS

Abstract

The exploitation of power inductors outside their linear region in switching converters can be achieved by raising the current until a decrease in the inductance can be noticed. This allows using a smaller magnetic core, increasing the power density of the converter. On the other hand, a detailed description of the magnetization curve including the temperature is required. Since this information is often not included in the inductor’s datasheets, this paper shows how to identify the behavior of an inductor when it is operated up to saturation and its temperature rises. In order to characterize the inductor in real operating conditions, a dedicated measurement rig was developed. It consists of a switching converter that encompasses the inductor under test and is controlled by a virtual instrument developed in LabVIEW. The characterization system was tested by retrieving the inductance and the magnetization curves vs. current for two commercial inductors at core temperatures up to 105 °C. The magnetic core was then characterized by the saturation current vs. inductance, obtaining an expression for the whole family of inductors sharing the same core. Finally, we experimentally analyzed the thermal transient of the inductors in operating conditions, confirming the fundamental role of the temperature in changing the current profiles and the core saturation condition.

EMI Worsening in a SMPS with Non-linear Inductor

“…To show the saturation effect, the inductor DO5010H-104 has been characterized by a dedicated measurement system from which the curve of inductance vs. current has been retrieved [26], [27]. Its characteristic curve is given in figure 3.…”

Assessment of the Current for a Non-Linear Power Inductor Including Temperature in DC-DC Converters

“…A third-order polynomial provides a good approximation for practical applications [10]. In contrast to saturable reactors operated in AC, the power inductors used in SMPSs operate with a DC offset and superimposed AC signal; therefore, a suitable characterization system is required [14]. To include the temperature dependence in the model, polynomial coefficients were considered linearly dependent on the temperature, meaning that the magnetic flux for a given magnetizing current depends linearly on the temperature.…”

“…The value of L sat is often lacking in the manufacturers' datasheet, where saturation is often considered to be the point at which the inductance is reduced by 10% only. For these reasons, a suitable characterization by a test rig was performed to retrieve a complete knowledge of the inductor [14]. Furthermore, the knowledge of the inductor-saturated model is particularly important for implementing virtual sensors or control actions that allow the estimation of the inductor current [15].…”

“…The main novelty of this paper consists of the exploitation of the polynomial inductor model to solve the differential equation of the non-linear inductor and to implement the flux model in closed form within a circuit simulator. The model has been previously developed [14]; here it is used to carry out the current shape. It is also of interest to industry, since it addresses the design based on the knowledge of the maximum current flowing through the inductor that flows through the power switch as well.…”

“…The main models proposed in the literature are arctan [1] and polynomial models [14]. The two models provide a different approach that can be recognized depending on the desired trade-off between the accuracy and calculation resources [23,24].…”