Daniel Kuebrich

Multi-resonant LCC converter - comparison of different methods for the steady-state analysis

Several different approaches for the investigation of the steady-state properties of resonant converters have been published. In addition to solving the occurring equations in the time domain, which turns out to be quite cumbersome, the designer can make use of approximate approaches in the frequency domain. Two of these methods are compared to the exact solution with regard to their accuracy and mathematical complexity within this paper for the multi-resonant LCC converter with inductive output filter. Additionally, a minimized set of nonlinear equations is derived in case of the exact solution based upon the state-plane technique.

Consideration of conduction losses for the series resonant converter by means of a simple extension to the SPA approach

The cumbersome derivation of the steady-state characteristics of resonant converters can be simplified by means of the state-plane analysis. Under the assumption of ideal components, a closed-form solution can be derived in case of the series resonant converter above the resonant frequency. However, losses due to parasitic resistances cannot be easily included within this approach. Nevertheless, a more precise prediction of the converterpsilas output characteristics taking the conduction losses into account is desirable. Therefore this paper describes a simple extension to the regular approach that leads to better agreement with measurements. This approach is based on the results derived under ideal assumptions, thus avoiding a more complicated and tedious analysis including the conduction losses.

Comparison of methods for the analysis of the parallel resonant converter with capacitive output filter

Several different approaches for the investigation of the steady-state properties of resonant converters have been published to date. In addition to solving the occurring equations in the time domain, which turns out to be quite cumbersome, the designer can make use of approximate approaches in the frequency domain. Two of these methods are compared to the exact solution with regard to their accuracy and mathematical complexity within this paper for the parallel loaded resonant LC converter with capacitive output filter. Some practical aspects are discussed by means of measured voltage conversion ratios.

Characterization of a modified LISN for effective separated measurements of common mode and differential mode EMI noise

The compliance with standards calls for proper designed EMI filters. EMI typically comprises common mode (cm) and differential mode (dm) noise. A systematic optimization of EMI filters requires the knowledge of the contribution and distribution of these two noise sources. The paper discusses different methods that allow the independent measurement of cm and dm noise. One suitable method described in detail integrates the separation set-up into the Line Impedance Stabilization Network (LISN). However, a correct interpretation of the measured results requires a characterization of the unavoidable modal conversion of the complete set-up - i.e. the measured level at the dm output in case of pure cm excitation and vice versa. As shown in this paper, the implementation of a standard LISN introduces a high amount of imperfections causing the undesired modal conversion. Thus, for the first time, this paper describes the characterization of the whole set-up including the LISN.

Efficiency improvement of a flyback converter by employing a stepped air-gap transformer

This paper introduces a flyback converter utilizing a stepped air-gap transformer. By employing such a transformer, the converter efficiency can be noticeably improved in comparison to a conventional flyback converter. Measurements confirm a total loss reduction of up to 6.4 %.

Automatic measurement of the reverse recovery behavior of ultra-fast diodes

Often data sheets provide only poor information about the recovery behavior of ultra-fast diodes. On the other hand, existing diode models do not predict the real characteristic for all diodes. Nevertheless, due to its importance, this behavior needs to be known and therefore measured. For this purpose, a fully automated measurement set-up for determining the reverse recovery characteristic of ultra-fast diodes in an accurate manner was designed and is described here. All the data obtained is immediately transferred into MATLAB and therefore available for further calculation, model building and model validation. Since the whole set-up is automated, a complete field of variations in the reverse voltage, the forward current, the temperature, and the di/dt can be easily applied to the tested diode. Hence, a lot of information can be obtained effortlessly. This uncomplicated methodology makes it readily available for circuit designers, allowing them to predict the contribution of the reverse recovery of rectifiers to the total losses more accurately. In addition, a real comparison of different diodes at many operation points is made possible.

Characterisation of an effective EMI noise separation including a standard LISN

The compliance with standards calls for proper designed EMI filters. EMI typically comprises common mode (cm) and differential mode (dm) noise. A systematic optimization of EMI filters requires the knowledge of the contribution and distribution of these two noise sources. The paper discusses different methods that allow the independent measurement of cm and dm noise. One suitable method described in detail integrates the separation set-up into the Line Impedance Stabilization Network (LISN). However, a correct interpretation of the measured results requires a characterization of the unavoidable crosstalk of the complete set-up - i.e. the measured level at the dm output in case of pure cm excitation and vice versa. As shown in this paper, the implementation of a standard LISN introduces the highest amount of imperfections causing the undesired crosstalk. Thus, for the first time, this paper describes the characterization of the whole set-up including the LISN.

Analytical calculation of the current depending inductance of a stepped air gap inductor

Magnetic devices are essential components in the field of power electronics. Exploiting the non-linear behavior of inductors and transformers offers the great merit of increasing the performance of switch mode power supplies. For instance, the light-load efficiency of a buck voltage regulator can be improved by using a non-linear inductor with stepped air gap. Moreover, non-linear chokes can be used for passive power factor correction or are employed in solar PV systems. For an optimal design, however, a controlled decrease in inductance at a larger current is required. Such a characteristic is displayed by inductors with stepped air gaps. To optimize the gap geometry, the knowledge of the exact behavior of the non-linear choke is crucial. As simulation tools require rather long computation times in order to calculate the non-linear characteristic, the authors chose a different approach. This paper demonstrates the analytical calculation of the current depending inductance of pot cores with stepped air gap. By solving a boundary value problem the magnetic vector potential inside the winding area is obtained assuming linear core material. Subsequently, the non-linearity of the core material is incorporated by decomposing the original non-linear problem into linear subproblems. Following this, the solution of the original problem is composed by using the solutions of the linear subproblems. Once the magnetic vector potential as a function of inductor current has been determined, the current depending inductance can be calculated. Results derived from both simulations with COMSOL Multiphysics and measurements show good agreement with the theoretical predictions.

Prediction of the non-linear behavior of a stepped air gap inductor

Magnetic devices are essential components in the field of power electronics. Exploiting the non-linear behavior of inductors and transformers offers the great merit of increasing the performance of switch mode power supplies. For an optimal design, however, a controlled decrease in inductance at a larger current is required. Such a characteristic is displayed by inductors with stepped air gaps. To optimize the gap geometry, the knowledge of the exact behavior of the non-linear choke is crucial. As simulation tools require rather long computation times in order to calculate the non-linear characteristic, the authors chose a different approach. This paper demonstrates the analytical calculation of the current depending inductance of pot cores with stepped air gap. Results derived from simulations with COMSOL Multiphysics and measurements show good agreement with the theoretical predictions.

Power loss measurement based on transient temperature rise

A calorimetric method for the determination of losses by means of transient temperature rise is applied to a basic switching cell. The method generally offers a very short measuring time in combination with high accuracy. However, an appropriate characterization of the set-up is crucial which usually implies a large effort. Hence, a simplified thermal model is introduced which minimizes this effort while still obtaining a high accuracy. In addition an elaborate but easy to use calibration and determination procedure is proposed. The result is a power loss measurement method based on calorimetry with a degree of accuracy which could be hardly reached by an electrical measurement. In comparison to common calorimetric methods the measurement time can be dramatically reduced. The method is used to verify predicted losses of a PFC boost converter.