Emerson unidrive m200 - Current Limit Operation; Torque Control; Supply Loss and Standard Ramp; Current Magnitude;Torque Producing Current

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for the user to adjust the performance of the controller. 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 is

inherent in the loop. The integral term must be increased enough to counter the effect of the ramp which is still active even in current limit. For example,

if the drive is operating at constant frequency and is overloaded the current limit system will try to reduce the output frequency to reduce the load. 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 of instability will

occur when operating around the point where field weakening begins. These oscillations can be reduced by increasing the proportional gain. A system

has been included to prevent regulation because of the opposite actions of the ramps and the current limit. This can reduce the actual level that the

current limit becomes active by up to 12.5%. This still allows the current to increase up to the current limit set by the user.

However the current limit flag (Currentlimitactive (10.009)) could become active up to 12.5% below the current limit depending on the ramp rate being

used.

Torque control

Again the controller will normally operate with an integral term only, particularly below the point where field weakening begins. The first signs of

instability will appear around rated frequency, and can be reduced by increasing the proportional gain. The controller can be less stable in torque control

mode compared to when it is used for current limiting. This is because load helps to stabilise the controller, and under torque control the drive may

operate with light load. Under current limit the drive is often under heavy load unless the current limits are set at a low level.

Supply loss and standard ramp

The d.c. link voltage controller becomes active if supply loss detection is enabled and the drive supply is lost or standard ramp is being used

(RampModeSelect (02.004) > 0) and the motor is regenerating. The d.c. link controller attempts to hold the d.c. link voltage at a fixed level by

controlling the flow of current from the drive inverter into its d.c. link capacitors. The system is forced into current control mode and the output of the d.c.

voltage controller is fed into the current controller as shown below.

Although it is not usually necessary, the d.c. link voltage controller gain can be adjusted with the VoltageControllerGain (05.031). However, it may be

necessary to adjust the current controller gains to obtain the required performance. If the gains are not suitable it is best to set up the drive in torque

control first. Set the gains to a value that does not cause instability around the point at which field weakening occurs. Then revert back to open loop

frequency control in standard ramp mode. To test the controller the supply should be removed whilst the motor is running. It is likely that the gains can

be increased further if required because the d.c. link voltage controller has a stabilising effect, provided that the drive is not required to operate in torque

control mode.

Parameter 04.001 Current Magnitude

Short description Shows the instantaneous drive output current

Mode Open‑loop

Minimum −VM_DRIVE_CURRENT Maximum VM_DRIVE_CURRENT

Default Units A

Type 32 Bit Volatile Update Rate 16ms

Display Format Standard Decimal Places 2

Coding RO, FI, VM, ND, NC, PT

CurrentMagnitude (04.001) is the instantaneous drive output current scaled so that it represents the r.m.s. phase current in Amps under steady state

conditions.

Parameter 04.002 Torque Producing Current