News on drive and automation for machine builder

July 2021

Sustainability in automation

Energie efficency for synchronouse permanent magent motors

The synchronous motor has two dominant loss components. Ohm losses (commonly referred to as copper losses) occur with the current for torque generation, these increase with the current, i.e. the torque. In the case of the voltage for rotary field generation, magnetization losses (commonly referred to as iron losses) occur, these increase with the frequency, i.e. the speed.

Copper losses can be calculated directly with the current or torque and the torque constant of the motor.

Calculating the iron losses is somewhat more difficult. Therefore, it helps to make two simplifications. First, the copper losses are constant over the entire speed range and depend only on the torque. Second, the total losses have a quadratic course.

The nominal torque of a synchronous motor decreases quadratically with speed. While at standstill the efficiency is zero, since there is no movement, at maximum speed there is no more torque, which in turn corresponds to an efficiency of zero. In between, there is an optimum operating point for each motor, which is at about two thirds of the nominal torque.

If interested, we are happy to share all the formula, as well as description of the calculations. For all those who are mainly oriented to the solution, we are of course continuing to calculate exactly for your application.