2D Electromagnetic FEA of a 3-Phase Wound-Field Synchronous Machine in Ansys Maxwell

In an electric machine the magnetic field, the voltage it induces and the torque it produces are all tied together, and none of them can be measured until the machine is built. Electromagnetic finite element analysis (FEA) shows all three from one model.

In this project we modelled a primitive three-phase, two-pole, wound-field synchronous machine (the simplest practical form of the design) in Ansys Maxwell and solved it with the transient solver. The stator and rotor are M19 electrical steel, with a distributed three-phase winding in the stator and a DC field winding on the rotor. From that one model the study pulls the flux lines, the flux density, the airgap field that sets the back-EMF, and the torque at standstill and at speed.

With the rotor turning at 3000 rpm and only the field winding energised (open circuit), the flux lines show the magnetic circuit closing through the stator and rotor cores and crossing the airgap twice, once at each pole.

The flux density at the top of this page shows how strong that field is across the machine. It peaks at about 0.96 T in small spots around the stator slots, while most of the steel works at much lower flux densities. Read together, the two plots show both the shape of the magnetic circuit and where the steel is working hardest, which is where saturation would appear first as the machine is pushed harder.

Plotting the flux density around a circle in the middle of the airgap shows how the field is spread from one pole to the next. That airgap field is what sweeps past the stator coils as the rotor turns, so its shape sets the shape of the back-EMF induced in the stator winding.

Each step in the wave comes from one slot of the distributed field winding, building a staircase that approximates a sine wave. The closer that staircase gets to a sine, the smoother and more balanced the three-phase back-EMF, which is why the airgap field is a direct read on the quality of the magnetic design.

The torque was computed at standstill and at speed. At 3000 rpm the machine settles to a steady average torque, with a small ripple as the rotor turns past the slots:

That last result is the core of how a synchronous machine is controlled: the same machine, at the same speed, gives very different torque depending on where the stator field is aligned relative to the rotor.

From a single 2D transient model, the simulation delivers the full electromagnetic picture of the machine: the flux lines and flux density that show the field, the airgap flux density that shapes the back-EMF, and the torque that shows the work it can do and how the phase angle controls it. That is the kind of result that lets an electric machine be understood and improved on screen, before any lamination is cut or any coil is wound. Electric machines sit at the heart of the shift we describe in how simulation is powering electric vehicles and aerospace.