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Nonlinear Inductor

Model inductor with nonideal core

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Passive Devices

Description

The Nonlinear Inductor block represents an inductor with a nonideal core. A core may be nonideal due to its magnetic properties and dimensions. The block provides the following parameterization options:

Single Inductance (Linear)

The relationships between voltage, current and flux are defined by the following equations:

i=iL+vGp

v=NwdΦdt

Φ=LNwiL

where:

  • v is the terminal voltage.

  • i is the terminal current.

  • iL is the current through inductor.

  • Gp is the parasitic parallel conductance.

  • Nw is the number of winding turns.

  • Φ is the magnetic flux.

  • L is the unsaturated inductance.

Single Saturation Point

The relationships between voltage, current and flux are defined by the following equations:

i=iL+vGp

v=NwdΦdt

Φ=LNwiL (for unsaturated)

Φ=LsatNwiL±Φoffset (for saturated)

where:

  • v is the terminal voltage.

  • i is the terminal current.

  • iL is the current through inductor.

  • Gp is the parasitic parallel conductance.

  • Nw is the number of winding turns.

  • Φ is the magnetic flux.

  • Φoffset is the magnetic flux saturation offset.

  • L is the unsaturated inductance.

  • Lsat is the saturated inductance.

Magnetic Flux Versus Current Characteristic

The relationships between voltage, current and flux are defined by the following equations:

i=iL+vGp

v=NwdΦdt

Φ=f(iL)

where:

  • v is the terminal voltage.

  • i is the terminal current.

  • iL is the current through inductor.

  • Gp is the parasitic parallel conductance.

  • Nw is the number of winding turns.

  • Φ is the magnetic flux.

Magnetic flux is determined by one-dimensional table lookup, based on the vector of current values and the vector of corresponding magnetic flux values that you provide. You can construct these vectors using either negative and positive data, or positive data only. If using positive data only, the vector must start at 0, and the negative data will be automatically calculated by rotation about (0,0).

Magnetic Flux Density Versus Magnetic Field Strength Characteristic

The relationships between voltage, current and flux are defined by the following equations:

i=iL+vGp

v=NwdΦdt

Φ=BAe

B=f(H)

H=NwleiL

where:

  • v is the terminal voltage.

  • i is the terminal current.

  • iL is the current through inductor.

  • Gp is the parasitic parallel conductance.

  • Nw is the number of winding turns.

  • Φ is the magnetic flux.

  • B is the magnetic flux density.

  • H is the magnetic field strength.

  • le is the effective core length.

  • Ae is the effective core cross-sectional area.

Magnetic flux density is determined by one-dimensional table lookup, based on the vector of magnetic field strength values and the vector of corresponding magnetic flux density values that you provide. You can construct these vectors using either negative and positive data, or positive data only. If using positive data only, the vector must start at 0, and the negative data will be automatically calculated by rotation about (0,0).

Magnetic Flux Density Versus Magnetic Field Strength Characteristic with Hysteresis

The relationships between voltage, current and flux are defined by the following equations:

i=iL+vGp

v=NwdΦdt

Φ=BAe

B=μ0(H+M)

H=NwleiL

where:

  • v is the terminal voltage.

  • i is the terminal current.

  • iL is the current through inductor.

  • Gp is the parasitic parallel conductance.

  • Nw is the number of winding turns.

  • Φ is the magnetic flux.

  • B is the magnetic flux density.

  • μ0 is the magnetic constant, permeability of free space.

  • H is the magnetic field strength.

  • M is the magnetization of the inductor core.

  • le is the effective core length.

  • Ae is the effective core cross-sectional area.

The magnetization acts to increase the magnetic flux density, and its value depends on both the current value and the history of the field strength H. The Jiles-Atherton [1, 2] equations are used to determine M at any given time. The figure below shows a typical plot of the resulting relationship between B and H.

In this case the magnetization starts as zero, and hence the plot starts at B = H = 0. As the field strength increases, the plot tends to the positive-going hysteresis curve; then on reversal the rate of change of H, it follows the negative-going hysteresis curve. The difference between positive-going and negative-going curves is due to the dependence of M on the trajectory history. Physically the behavior corresponds to magnetic dipoles in the core aligning as the field strength increases, but not then fully recovering to their original position as field strength decreases.

The starting point for the Jiles-Atherton equation is to split the magnetization effect into two parts, one that is purely a function of effective field strength (Heff) and the other an irreversible part that depends on past history:

M=cMan+(1c)Mirr

The Man term is called the anhysteretic magnetization because it exhibits no hysteresis. It is described by the following function of the current value of the effective field strength, Heff:

Man=Ms(coth(Heffα)αHeff)

This function defines a saturation curve with limiting values ±Ms and point of saturation determined by the value of α, the anhysteretic shape factor. It can be approximately thought of as describing the average of the two hysteretic curves. In the Nonlinear Inductor block, you provide values for dMan/dHeffwhen Heff = 0 and a point [H1, B1] on the anhysteretic B-H curve, and these are used to determine values for α and Ms.

The parameter c is the coefficient for reversible magnetization, and dictates how much of the behavior is defined by Man and how much by the irreversible term Mirr. The Jiles-Atherton model defines the irreversible term by a partial derivative with respect to field strength:

dMirrdH=ManMirrKδα(ManMirr)δ={1if H01if H<0 

Comparison of this equation with a standard first order differential equation reveals that as increments in field strength, H, are made, the irreversible term Mirr attempts to track the reversible term Man, but with a variable tracking gain of 1/(Kδα(ManMirr)). The tracking error acts to create the hysteresis at the points where δ changes sign. The main parameter that shapes the irreversible characteristic is K, which is called the bulk coupling coefficient. The parameter α is called the inter-domain coupling factor, and is also used to define the effective field strength used when defining the anhysteretic curve:

Heff=H+αM

The value of α affects the shape of the hysteresis curve, larger values acting to increase the B-axis intercepts. However, notice that for stability the term Kδα(ManMirr) must be positive for δ > 0 and negative for δ < 0. Therefore not all values of α are permissible, a typical maximum value being of the order 1e-3.

Procedure for Finding Approximate Values for Jiles-Atherton Equation Coefficients

You can determine representative parameters for the equation coefficients by using the following procedure:

  1. Provide a value for the Anhysteretic B-H gradient when H is zero parameter (dMan/dHeffwhen Heff = 0) plus a data point [H1, B1] on the anhysteretic B-H curve. From these values, the block initialization determines values for α and Ms.

  2. Set the Coefficient for reversible magnetization, c parameter to achieve correct initial B-H gradient when starting a simulation from [H B] = [0 0]. The value of c is approximately the ratio of this initial gradient to the Anhysteretic B-H gradient when H is zero. The value of c must be greater than 0 and less than 1.

  3. Set the Bulk coupling coefficient, K parameter to the approximate magnitude of H when B = 0 on the positive-going hysteresis curve.

  4. Start with α very small, and gradually increase to tune the value of B when crossing H = 0 line. A typical value is in the range of 1e-4 to 1e-3. Values that are too large will cause the gradient of the B-H curve to tend to infinity, which is nonphysical and generates a run-time assertion error.

Sometimes you need to iterate on these four steps to get a good match against a predefined B-H curve.

Dialog Box and Parameters

Main Tab

Parameterized by

Select one of the following methods for block parameterization:

  • Single inductance (linear) — Provide the values for number of turns, unsaturated inductance, and parasitic parallel conductance.

  • Single saturation point — Provide the values for number of turns, unsaturated and saturated inductances, saturation magnetic flux, and parasitic parallel conductance. This is the default option.

  • Magnetic flux versus current characteristic — In addition to the number of turns and the parasitic parallel conductance value, provide the current vector and the magnetic flux vector, to populate the magnetic flux versus current lookup table.

  • Magnetic flux density versus magnetic field strength characteristic — In addition to the number of turns and the parasitic parallel conductance value, provide the values for effective core length and cross-sectional area, as well as the magnetic field strength vector and the magnetic flux density vector, to populate the magnetic flux density versus magnetic field strength lookup table.

  • Magnetic flux density versus magnetic field strength characteristic with hysteresis — In addition to the number of turns and the effective core length and cross-sectional area, provide the values for the initial anhysteretic B-H curve gradient, the magnetic flux density and field strength at a certain point on the B-H curve, as well as the coefficient for the reversible magnetization, bulk coupling coefficient, and inter-domain coupling factor, to define magnetic flux density as a function of both the current value and the history of the field strength.

Number of turns

The total number of turns of wire wound around the inductor core. The default value is 10.

Unsaturated inductance

The value of inductance used when the inductor is operating in its linear region. This parameter is visible only when you select Single inductance (linear) or Single saturation point for the Parameterized by parameter. The default value is 2e-4 H.

Saturated inductance

The value of inductance used when the inductor is operating beyond its saturation point. This parameter is visible only when you select Single saturation point for the Parameterized by parameter. The default value is 1e-4 H.

Saturation magnetic flux

The value of magnetic flux at which the inductor saturates. This parameter is visible only when you select Single saturation point for the Parameterized by parameter. The default value is 1.3e-5 Wb.

Current, i

The current data used to populate the magnetic flux versus current lookup table. This parameter is visible only when you select Magnetic flux versus current characteristic for the Parameterized by parameter. The default value is [ 0 0.64 1.28 1.92 2.56 3.20 ] A.

Magnetic flux vector, phi

The magnetic flux data used to populate the magnetic flux versus current lookup table. This parameter is visible only when you select Magnetic flux versus current characteristic for the Parameterized by parameter. The default value is [0 1.29 2.00 2.27 2.36 2.39 ].*1e-5 Wb.

Magnetic field strength vector, H

The magnetic field strength data used to populate the magnetic flux density versus magnetic field strength lookup table. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic for the Parameterized by parameter. The default value is [ 0 200 400 600 800 1000 ] A/m.

Magnetic flux density vector, B

The magnetic flux density data used to populate the magnetic flux density versus magnetic field strength lookup table. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic for the Parameterized by parameter. The default value is [ 0 0.81 1.25 1.42 1.48 1.49 ] T.

Effective length

The effective core length, that is, the average distance of the magnetic path. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic or Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter. The default value is 0.032 m.

Effective cross-sectional area

The effective core cross-sectional area, that is, the average area of the magnetic path. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic or Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter. The default value is 1.6e-5 m^2.

Anhysteretic B-H gradient when H is zero

The gradient of the anhyseretic (no hysteresis) B-H curve around zero field strength. Set it to the average gradient of the positive-going and negative-going hysteresis curves. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter. The default value is 0.005 m*T/A.

Flux density point on anhysteretic B-H curve

Specify a point on the anhysteretic curve by providing its flux density value. Picking a point at high field strength where the positive-going and negative-going hysteresis curves align is the most accurate option. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter. The default value is 1.49 T.

Corresponding field strength

The corresponding field strength for the point that you define by the Flux density point on anhysteretic B-H curve parameter. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter. The default value is 1000 A/m.

Coefficient for reversible magnetization, c

The proportion of the magnetization that is reversible. The value should be greater than zero and less than one. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter. The default value is 0.1.

Bulk coupling coefficient, K

The Jiles-Atherton parameter that primarily controls the field strength magnitude at which the B-H curve crosses the zero flux density line. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter. The default value is 200 A/m.

Inter-domain coupling factor, alpha

The Jiles-Atherton parameter that primarily affects the points at which the B-H curves intersect the zero field strength line. Typical values are in the range of 1e-4 to 1e-3. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter. The default value is 1e-4.

Parasitic parallel conductance

Use this parameter to represent small parasitic effects. A small parallel conductance may be required for the simulation of some circuit topologies. The default value is 1e-9 1/Ω.

Interpolation option

The lookup table interpolation option. This parameter is visible only when you select Magnetic flux versus current characteristic or Magnetic flux density versus magnetic field strength characteristic for the Parameterized by parameter. Select one of the following interpolation methods:

  • Linear — Uses a linear interpolation function.

  • Cubic — Uses the Piecewise Cubic Hermite Interpolation Polynomial (PCHIP).

For more information on interpolation algorithms, see the PS Lookup Table (1D) block reference page.

Initial Conditions Tab

Specify initial state by

Select the appropriate initial state specification option:

  • Current — Specify the initial state of the inductor by the initial current through the inductor (iL). This is the default option.

  • Magnetic flux — Specify the initial state of the inductor by the magnetic flux.

This parameter is not visible when you select Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter on the Main tab.

Initial current

The initial current value used to calculate the value of magnetic flux at time zero. This is the current passing through the inductor. Component current consists of current passing through the inductor and current passing through the parasitic parallel conductance. This parameter is visible only when you select Current for the Specify initial state by parameter. The default value is 0 A.

Initial magnetic flux

The value of magnetic flux at time zero. This parameter is visible only when you select Magnetic flux for the Specify initial state by parameter. The default is 0 Wb.

Initial magnetic flux density

The value of magnetic flux density at time zero. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter on the Main tab. The default is 0 T.

Initial field strength

The value of magnetic field strength at time zero. This parameter is visible only when you select Magnetic flux density versus magnetic field strength characteristic with hysteresis for the Parameterized by parameter on the Main tab. The default is 0 A/m.

Ports

The block has the following ports:

+

Positive electrical port

-

Negative electrical port

Examples

For comparison of nonlinear inductor behavior with different parameterization options, see the Nonlinear Inductor Characteristics example.

The Inductor With Hysteresis example shows how modifying the equation coefficients of the Jiles-Atherton magnetic hysteresis equations affects the resulting B-H curve.

References

[1] Jiles, D.C and D.L. Atherton. "Theory of ferromagnetic hysteresis." Journal of Magnetism and Magnetic Materials. Vol. 61, 1986, pp. 48–60.

[2] Jiles, D.C and D.L. Atherton. "Ferromagnetic hysteresis." IEEE® Transactions on Magnetics. Vol. 19, No. 5, 1983, pp. 2183–2184.

See Also

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