I have two types of machines which have a water jet drive, together with a motor. one has an inverter driven DC motor the other an inverter driven AC motor. If the water jet makes the load run faster than the set speed of the motor, can/does the different type of motor allow itself to be quot;pulledquot; round faster? or is a braking force applied to the motor. I am mostly interested the difference, if any between AC and DC motor in this respect,or will both do the same job depending on how the inverter is set up.
Both an AC motor and a DC motor can apply braking force if the load exerts torque tending to increase the motor speed. When applying braking torque, either type of motor will function as a generator and transfer power from the load to the power source. A load that applies torque in the direction that would increase the motor speed is often called an “overhauling load.” An AC motor control inverter, more often called a variable-frequency drive (VFD), is normally not designed to accept energy returned from the motor. A standard VFD can be expected have some means of protection that might allow a limited speed increase and de-energize the motor if the limit is exceeded. If the motor id de-energized, it will be driven to a higher speed by the load, but most AC motors can tolerate being driven considerably above the normal speed. VFDs can be purchased with a dynamic braking circuit that will dissipate braking energy in resistors or a regenerative circuit that will return braking energy to the AC power source. Sometimes a small amount of dynamic braking control capacity is included in a standard VFD, but resistors usually need to be added externally. A DC motor controller is usually a converter or chopper. The controller for a permanent magnet DC motor might be called an inverter, and the function would be the same as a VFD controlled permanent magnet synchronous motor. DC motor controllers can be furnished with either dynamic braking or regenerative braking. DC motors are generally less tolerant of over-speed operation.
