Origin of Parasitic Time-Periodic Torques and Forces in Electrical Machines

The origins of the time-periodic torques and forces acting on the rotor of an electrical machine are searched for. The main task of an electrical machine operated in a steady state is to produce a constant torque. In an ideal case, this would be the only magnetic force on the rotor. In practice, the electromagnetic torque usually has relatively large ripple and significant lateral forces may also occur. The examples discussed are from radial flux machines, especially, from cage induction motors. As the electromagnetic torque and forces can be calculated from the air-gap magnetic field, the air-gap flux density and its harmonics are under special examination. Understanding the magnetic interactions may provide means to actively control the air-gap flux density and eliminate the parasitic effects.