One of the fundamental properties of a permanent magnet synchronous motor is the relationship between its current and torque (torque-current curve). The torque generated at each current value is uniform with increases in current up to a certain point, so the torque increases in a linear fashion. However, magnetic saturation effects occur with further current increases, and the torque generated with each increase in current begins to drop off.
Because a permanent magnet synchronous motor’s torque-current curve is highly susceptible to saturation effects in the motor’s magnetic circuit, it is helpful to obtain the torque-current curve with a magnetic field analysis taking saturation into account in order to evaluate the motor’s design and drive characteristics.
This Application Note presents how to obtain the torque-current curve as a basic property of one type of permanent magnet synchronous motor, the surface permanent magnet synchronous (SPM) motor.