Variable Reluctance

Variable reluctance in electromagnetic systems


Magnetic Elements


The Variable Reluctance block models a variable reluctance, that is, a component that resists flux flow. The ratio of the magnetomotive force (mmf) across the component to the resulting flux that flows through the component is defined as the reluctance, and is dependent on the value of the input physical signal.

The block is based on the following equations:




MMFMagnetomotive force (mmf) across the component
ΦFlux through the component
XValue presented at the physical signal port
μ0Permeability constant
μrRelative permeability of the material
ACross-sectional area of the section being modeled

Connections N and S are magnetic conserving ports. The mmf across the reluctance is given by MMF(N)MMF(S), and the sign of the flux is positive when flowing through the device from N to S.


Use the Variables tab in the block dialog box (or the Variables section in the block Property Inspector) to set the priority and initial target values for the block variables prior to simulation. For more information, see Set Priority and Initial Target for Block Variables.


Minimum length or thickness X>=0

The minimum value of length of air gap or thickness of section. If the input signal falls below this level (for example, turns negative), this minimum value is used. The parameter value must be nonnegative. The default value is 0.

Cross-sectional area

Area of the section being modeled. The default value is 0.01 m^2.

Relative permeability of material

Relative permeability of the section material. The default value is 1.


The block has the following ports:


Magnetic conserving port associated with the block North terminal.


Magnetic conserving port associated with the block South terminal.

The block also has one physical signal input port that provides the value of the length of air gap or thickness of section.

Introduced in R2010a

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