Volume 61 Issue 2 (2011) - Годишник на ТУ - София - Технически ...

pends on the results of the thermal field. The electrical conductivity is with temperaturedependent value, which influences the electric current in coil region. Indirectcoupling between the two problems (magnetic field and thermal one) has been utilized.The two problems are solved successively and after each solution the values ofelectromagnetic force and average temperature are stored.3.4. Circuit ModelThe electromagnet is powered by controllable power electronic block presented by itscircuit. Electric circuit equation for the electromagnet coil is (7)d( )u R(T ) i (7)dtwhere u is the supplied voltage;R(T) is the resistance of the coil;i is the coil current;ψ is the flux linkage.The current i flowing in the coil is a nonlinear function of flux linkage ψ that, in turn,is a function of air-gap δ and core magnetizationdiu R( T ) i L( , )(8)dtCommonly the values of magnetic inductance must be predefined as function to solve(8). Here needed inductance values are FEM determinated only for ψ and δ of currentload step.Fig.3. Coupled field problem block diagram.Mechanical motion equation (9) must be included due to movable electromagnet core2d m F F (9)20dtwhere F is the electromagnetic force and F 0 is the initial force halting the armature.Air-gap is calculated in each time step using electromagnetic force.117