Research On Broadband Modeling Theory And Static Capacitance Calculation Method Of Inductive Components

With the development of power electronics,the operating voltage,operating frequency and power density of power conversion devices and switching power supplies are constantly increasing.As a result,the demand for system EMC performance has also increased,with inductive components such as transformers and inductors being one of the hot spots for EMC research,and they have a wide range of applications in electric vehicles,DC power transmission and pulsed power.Under high frequency conditions,inductive components can produce serious stray inductance and parasitic capacitance,and the self-capacitance between current-carrying coils has a nonnegligible effect on their transfer function and frequency response,and their characteristics have a large impact on the overall performance of the circuit.Therefore,the establishment of a broadband model of inductive components with distributed parameters is of great significance for the in-depth study of electromagnetic interference problems caused by inductive components.This paper firstly investigates the broadband model of basic passive devices and their amplitude-frequency characteristics,and briefly describes the principles of broadband modelling,explores the variation of the electrical characteristics of devices at high frequencies,and uses this as a theoretical basis for subsequent modelling.Secondly,the commonly used methods for extracting parasitic parameters of inductive components in the existing literature are summarised and their advantages and disadvantages are analysed.Finally,a method is proposed for extracting the parameters of the broadband model of inductive components based on the impedance and amplitude frequency characteristics measurements,i.e.,the impedance information and frequency characteristics of the external ports of inductive components are measured using an impedance analyser to calculate and extract the parameters of the broadband model.Considering that the structure and operating principles of transformers and common mode chokes are somewhat different and that the modelling processes are also different,this paper illustrates the ideas and methods of wideband modelling using two typical inductive components,transformers and common mode chokes,as examples.In this case,the transformer is modelled using a broadband model with three capacitors,and its parasitic parameters are measured and calculated in a combination of methods.The modelling process of the common mode inductor is based on the transformer,and on the basis of a detailed analysis of the common mode and differential mode path models of the common mode choke,the two are combined to build a common mode choke full circuit wideband model,and a differential mode impedance correction method is proposed to improve the accuracy of the model for the frequency variation characteristics of the differential mode inductor.This broadband model construction method can be used for modelling simulation,design and optimisation of systems such as electromagnetic interference filters.In addition,the frequency variation characteristics of the core can affect the winding leakage inductance and hence the accuracy of the differential mode path model,so the expression of the differential mode path model impedance is optimised by non-linear fitting.Based on the extraction strategy of the parasitic capacitance of inductive components,it is found that the winding method of inductive components affects the magnitude of the parasitic capacitance by deriving the theoretical equation of static capacitance,and the accuracy of the existing static capacitance calculation method is not high as verified by finite element simulation.In this paper,an improved method for calculating the static capacitance between conductors of solid circular cross-section is proposed,starting from the mechanism of the parasitic capacitance of inductive elements.The static capacitance calculation method with a hyperbolic integration path is proposed,taking into account the influence of the winding size and structure of the inductive element on the electric field coupling and energy distribution.The accuracy of the improved static capacitance calculation method is verified by constructing a finite element model of the static capacitance between the turns of two conductors.In general,inductive element windings are available in two winding forms,orthogonal stacking and staggered stacking.From the calculation method of inter-conductor capacitance,the static capacitance calculation methods of the two winding forms only differ slightly in the integration angle,and in order to obtain more accurate capacitance values,finite element simulation is used to extract parameters and verify the accuracy of the calculation results of the method proposed in this paper.Finally,a hollow inductor coil with a single winding is prepared to simulate a quadrature stacked coil and the experimental parameters are extracted,showing that the experimental and calculated results match.On the basis of the extraction strategy of the parasitic capacitance of the inductive element,by deriving the theoretical formula of the static capacitance,it can be found that the winding method of the inductive element will affect the size of the parasitic capacitance,and the finite element simulation verifies that the existing static capacitance calculation method is not accurate.For this reason,this article starts with the generation mechanism of the parasitic capacitance of inductive components,and proposes an improved method for calculating the static capacitance between solid circular cross-section conductors.Taking into account the influence of the winding size and structure of the inductive component on the electric field coupling and energy distribution,the static capacitance calculation method of the hyperbolic integral path is proposed.By constructing a finite element model of static capacitance between turns of two conductors,the accuracy of the improved static capacitance calculation method is verified.Generally speaking,inductive component windings have two winding forms:orthogonal stacking and staggered stacking.From the calculation method of capacitance between conductors,the static capacitance calculation methods of the two winding forms only have a small difference in the integral angle.The accurate capacitance value is extracted by finite element simulation method and the accuracy of the calculation result of the method proposed in this paper is verified.Finally,an aircore inductor coil with a single-layer winding is prepared to simulate the orthogonal stacked coil and the experimental parameters are extracted.The results show that the experimental and calculated results are consistent.This paper proposes a method for modelling the broadband of inductive components and calculating their parasitic capacitance based on parametric measurements,which provides a theoretical basis for predicting the performance parameters of inductive components and analysing electromagnetic interference.