1,720,997 research outputs found
A Quasi-Constant On-Time Control for SMPS with a Non-linear Inductor based on Power Switch Conduction Time Estimation
Full text linkThis paper proposes a control method for switching-mode power supplies equipped with non-linear inductors; the method is based on the estimation of the conduction time (TON) of the power switch. The TON value is tuned according to the inductor model to obtain Quasi Constant On-Time control. The method is devised for ferrite core power inductor, the non-linearity is exploited up to saturation, condition where the differential inductance is reduced to half of its maximum value. This approach allows the calculation of the conduction time TON such that the maximum current of the inductor always corresponds to the saturation value while also considering the inductor temperature. This method obtains the current peak versus TON through a proper inductor model and a recursive algorithm for a given inductor temperature. The theoretical analysis was verified on a boost converter by comparing the simulations with experimental data with different loads, showing that the operating current can be increased by approximately 40% avoiding thermal runaway
Graded reflectivity micromirror arrays
No full textA technique for fabricating arrays of graded reflectivity micromirrors with diameters as small as 25 μm is reported. It is based on laser-induced physical vapor deposition through microholes on a thin freestanding noncontact mask, and it is suitable for applications in micro-optics and solid-state laser technology. © 2002 Optical Society of America
Characterization of inductors in partial saturation including thermal effects for DC/DC converters
No full textModern switching power electronic converters are widely used in many industrial and consumer applications, especially in step-up and step-down configurations. The optimization of the inductor in the converter design gives advantages in terms of power density increase and cost reduction; therefore, to properly design the converters, it is necessary to improve the knowledge of magnetic material behaviour as the current changes. The development of new models is becoming crucial in the design of modern power converters and there are some recent papers dealing with the use of inductors working in partial saturation [1-5]. This issue is of great interest for scientists and industry due to economic reasons tied both to the initial cost of the converter and to the reduced pay-back time of the equipment.
Since available measurement systems are usually not well suited to test inductors in high current operating conditions, a dedicated system based on a DC/DC buck converter, in which its inductor represents the inductor under test and the load is a constant current sink, has been set up (Fig. 1). A virtual instrument that allows automatic inductance measurements has been implemented in LabVIEW® programming environment; the front panel of the instrument is shown in Fig. 2. These tests are performed on the same inductor as the current changes, in order to plot the inductance L versus the inductor current I at a fixed temperature. For the experimental measurement a test rig has been set up, the elements of which are listed in Table 1. Using the proposed measurement system, a family of isothermal inductance curves has been obtained for the inductor under test. The aggregate data relative to a 470μH Panasonic inductor (ELC18B471L) are shown in a 3-D surface in Fig. 3. For current lower than 2.5A the curves are similar and there is no significant temperature effect on the value of inductance. The same observation is valid for current higher than 4.5A; at this point, the inductance drops to 20% of the nominal value and the inductor is in deep saturation region. In the rolloff region, between 2.5A and 4.5A, it can be noted that for higher temperatures the inductance curves shift downwards, indicating a smaller inductance. As the inductor approaches the deep saturation region, the temperature minimizes his effect on the inductance variation. As expected, the operation with large currents signal highlights the variation of the inductance with temperature.
These curves can be used in the design process for applications which involve inductors operating in moderate saturation region since it is possible to obtain a model based on polynomials including also the temperature effect. It has been underlined that the isothermal curves can be approximated by fifth-degree polynomials and that it can be assumed that the inductance depends linearly from temperature (Fig.4)
Impact of Nonlinear Inductor on Efficiency and Power Losses in a SMPS: a Case Study
No full textThis paper proposes a comparative analysis focused on losses in two Switched Mode Power Supplies, adopting a linear inductor and an inductor operated up to saturation, respectively. The use of the nonlinear inductor saves weight and cost on the magnetic material, which is of great interest for automotive applications; however, it increases the peak current and can increase losses. The analysis aims to compare, by simulations, the impact on the efficiency of the different current waveforms throughout the converter. The losses are discussed in detail and calculated for each component of the converters
Design and Modeling of an Interleaving Boost Converter with Quasi-Saturated Inductors for Electric Vehicles
No full textThis paper is focused on the analysis and modeling of DC-DC boost converters in interleaving configuration exploiting inductors in the quasi-saturation region. The converter is designed to optimize the power density by minimizing the size of the inductors. A simulation study for electric vehicle applications is conducted analyzing the effects of duty cycle and temperature variation on the ripple of the input current giving, moreover, information on the performances and dynamics of the converter for further implementation and optimizations
Assessment of the Current for a Non-Linear Power Inductor Including Temperature in DC-DC Converters
Full text linkA method for estimating the current flowing through a non-linear power inductor operating in a DC/DC converter is proposed. The knowledge of such current, that cannot be calculated in closed form as for the linear inductor, is crucial for the design of the converter. The proposed method is based on a third-order polynomial model of the inductor, already developed by the authors; it is exploited to solve the differential equation of the inductor and to implement a flux model in a circuit simulator. The method allows the estimation of the current up to saturation, intended as the point at which the differential inductance is reduced to half of its maximum value. The current profile depends also on the inductor temperature. Based on this, the influence of core temperature on the conduction time of the power switch was determined. This study shows that the exploitation of saturation requires a proper value of the conduction time value that depends on the temperature. The theoretical analysis has been experimentally verified on a boost converter and is valid for the entire class of DC-DC converters in which the power inductor is subjected to a constant voltage for a given time. The simulations agree with the experimental data from a case study concerning conduction time and temperature
EMI Filter Re-Design in a SMPS with Inductor in Saturation
Full text linkThis paper analyzes the design issues of the input EMI (Electro-Magnetic Interference) filter's in a switching mode power supply where the power inductor is operated in saturation. Starting with a SMPS equipped with linear inductor, the input filter is firstly designed to comply with Standards. Then, a new inductor with a smaller core size is employed in the same SMPS to exploit saturation. The EMI filter is re-designed, taking into account the increase of EMI introduced by the non-linear operation of the inductor. Finally, the reduction of the inductor's size and cost is compared with the increased size and cost of the EMI filter
Self-Heating Induced Instability of a Non-Linear Inductor in a SMPS: a Case Study.
Full text linkThis paper proposes a case study to show that the non-linear operation of a power inductor in a SMPS can induce instability of the control system leading to overheating of the inductor beyond its allowable temperature and to an excessive peak of the maximum current. The case study is performed by a commercial ferrite inductor employed in a synchronous boost converter encompassing a control system to adjust the duty cycle, assuring a constant output voltage. The thermal transient is described by the time domain waveforms and thermal images
A Measurement System for Power Inductors in Non-Linear Operating Conditions
No full textThe exploitation of power inductors in switching converters outside the linear region requires detailed information on the magnetization curve that often is not included among those usually available on their datasheets. This paper proposes an automatic system in which the inductor is characterized in real operating conditions taking into account also the core temperature. It is based on a switching converter suitably controlled by a virtual instrument. The system was tested by retrieving the inductance vs current curves of two commercial inductors for core temperatures up to 105°C, showing the different behaviors of the magnetization curves. Results are coherent with data given by manufacturers and provide a complete characterization of the inductors
Non-Linear Inductors Characterization in Real Operating Conditions for Power Density Optimization in SMPS
Full text linkThe 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
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