Synchronous servo motor without field weakening

For a synchronous servo motor the maximum motor torque value is available up to the 'characteristic speed point' .

After the 'characteristic speed point' the maximum motor torque decreases with increasing speed. When the motor reach the theoretical no-load-speed, the motor torque is 0 Nm.

 

 

This is due to with the speed increasing induced voltage of the motor.

When approaching the induced voltage at the maximum output voltage of the inverter, the torque-generating current Iq reduced. Sequence, the motor torque decreases.

The maximum output voltage of the inverter is limited by the HV voltage.

When operating points on the 'characteristic speed point', the control reserve for the current controller is severely limited.

If you are using a battery, the HV voltage can vary by acceleration or recuperation. The HV voltage has a direct influence on the 'characteristic speed point' .

 

The induced voltage can be calculated using the following formula: