SK3401 15.0/18.5kW + SM-ProfinetEMERSON Control Techniques Commander

SK3401 15.0/18.5kW + SM-ProfinetEMERSON Control Techniques Commander 

These parameters control the proportional and integral gains of the current controller. As already mentioned the current controller either providescurrent limits or closed loop torque control bymodifying the drive output frequency. The control loop is also used in its torque mode during mains loss,or when the controlled mode standard ramp is active and the drive is decelerating, to regulate the flow ofcurrent into the drive. Although the defaultsettings have been chosen to give suitable gains for less demanding applications it may be necessary for the user to adjust the performance of thecontroller. The following is a guide to setting the gains for different applications.

Current limit operation

The current limits will normally operate with an integral term only, particularly below the point where field weakening begins. The proportional term isinherent in the loop. The integral term must beincreased enough to counter the effect of the ramp which is still active even in current limit. Forexample, if the drive is operating at constant frequency and is overloaded the current limit system willtry to reduce the output frequency to reduce theIoad. At the same time the ramp will try to increase the frequency back up to the demand level. If the integral gain is increased too far the first signs ofinstability will occur when operating around the point where field weakening begins. These oscillations can be reduced by increasing the proportionalgain. A system has been included toprevent regulation because of the opposite actions of the ramps and the current limit. This can reduce the actuallevel that the current limit becomes active by 12.5%. This still allows the current to increaseupto the current limit set by the user. However the currentimit flag (Pr 10.09) could become active up to 12.5% below the current limit depending on the ramp rate used.

Torque controlAgain the controller will normally operate with an integral term only, particularly below the point where field weakening begins. The first signs ofinstability will appear around rated speed, and can be reduced by increasing the proportional gain. The controller can be less stable in torque controlmode rather than when it is used for current limiting. This is because load helps to stabilisethe controller, and under torque control the drive mayoperate with light load. Under current limit the drive is often under heavy load unless the current limits are set at a low level.Mains loss and controlled standard ramp

The DC bus voltage controller becomes active if mains loss detection is enabled and the drive supply is lost or controlled standard ramp is being usedand the machine is regenerating. The DC bus controller attempts to hold the DC bus voltage at a fixed level by controlling the flow of current from thedrive inverter into its DC bus capacitors. The output of the DC bus controller is a current demand which is fed into the current PI controller as shown