Motor Torque-Speed Curves

This example shows a comparison of the torque-speed characteristics for five different motor types. To select the motor type, right-click on the Electric Motor block and select Block Parameters (Subsystem) from the context menu. In the new window, specify the desired motor using the Label mode active choice parameter. All motors have been sized for roughly the same mechanical power rating.

To run and compare all five motors, click on the hyperlink to plot characteristic curves. Understanding the torque-speed and power-speed behavior of a motor is critical when choosing a motor for a given application. Modify this model and its supporting library to compare specific motors based on their datasheet values. Critical parameters are typically starting torque (torque at zero RPM), and peak/maximum power and the corresponding RPM.

The DC Motor has a linear torque-speed characteristic, and power peaks at about half the maximum RPM. The Shunt Motor also has a linear torque-speed characteristic and similarly-shaped power curve. In practice a shunt motor cannot run at its peak power or torque as the currents involved are too large. This particular motor is designed to deliver a maximum 50 Watts of mechanical power at 4000 rpm.

The Universal Motor torque-speed characteristic follows 1/x^2 relationship. In this case, the relatively large starting torque is achieved with realistic current values. The power is just peaking at around 6000rpm. The Induction Motor torque-speed curve is typical of this type of motor having a low starting torque, and a peak torque just below synchronous speed. Note that both motoring and generating regions are plotted.

The Servomotor is a controlled servomotor with a maximum torque of 0.25 Nm. The torque demand is set to 0.2 Nm, which is achievable up to 4350rpm above which envelope limiting occurs. To see the permissible torque-envelope, set the Electric Motor variant choice to 'Servomotor', open the Electric Motor block and double click on the Servomotor block. The envelope is defined by the first two block parameters.

Model

Simulation Results from Simscape Logging

The plots below show characteristic curves for different types of motors.