When Variable Speed Drives (VSD) are installed, a motor plant identification routine is run when the motor is disconnected from the load. Hereby, the VSD determines the electrical characteristics (needed for accurate torque control) and inertia of the motor. However, at no point is any information about the load and gearbox (with which the reflected inertia could be calculated) entered into the VSD. I do not understand how a VSD can control the motor to achieve the desired angular rate within the specified time (settling time) without information about the load and gearbox.By controlling the current in the motor, the VSD controls the torque produced by the motor. In a speed control application, the VSD calculates the required torque to produce the desired angular rate, by means of a PI controller. To accurately calculate the gains of the PI controller to ensure the settling time is met, the physical model of the motor, gearbox and load (the plant) must be known. Please refer to the attached image. How is speed control implemented in practice without the VSD having an accurate plant model?My intuition is that it is assumed that the gearbox ratio is high enough and load inertia is small enough that the reflected inertia is negligible compared to the inertia of the motor.
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