Operating Modes

Servo control

3-107© Siemens AG 2006 All Rights ReservedSINAMICS S120 Function Manual, 03/2006 Edition

3.1.12 Optimizing the current and speed controller

General information

!Caution

Controller optimization may only be performed by skilled personnel with aknowledge of control engineering.

The following tools are available for optimizing the controllers:

� “Function generator” in STARTER

� “Trace” in STARTER

� “Measuring function” in STARTER

� CU320 measuring sockets

Optimizing the current controller

The current controller is initialized when the system is commissioned for the firsttime and is adequately optimized for most applications.

Optimizing the speed controller

The speed controller is set in accordance with the motor moment of inertia whenthe motor is configured for the first time. The calculated proportional gain is set toapproximately 30 % of the maximum possible gain in order to minimize vibrationswhen the controller is mounted on the mechanics of the machine for the first time.

The integral time of the speed controller is always preset to 10 ms.

� The following optimization measures are necessary in order to achieve the fulldynamic response:

– Increase the proportional gain Kp_n (p1460)

– Change the integral action time Tn_n (p1462)

Example of measuring the speed controller frequency response

By measuring the speed controller frequency response and the control system,critical resonance frequencies can, if necessary, be determined at the stability limitof the speed control loop and dampened using one or more current setpoint filters.This normally enables the proportional gain to be increased (e.g. Kp_n = 3* defaultvalue).

After the Kp_n value has been set, the ideal integral action time Tn_n (e.g. redu-ced from 10 ms to 5 ms) can be determined.

Operating Modes

Servo control

3-108© Siemens AG 2006 All Rights Reserved

SINAMICS S120 Function Manual, 03/2006 Edition

Example of speed setpoint step change

A rectangular step change can be applied to the speed setpoint via the speed set-point step change measuring function. The measuring function has preselected themeasurement for the speed setpoint and the torque-generating current.

Kp_n is optimum

––>OK

Kp_n is too high,overshoots

––>not OK

Kp_n is too low, dampedtransient response

––>OK, not optimum

Fig. 3-20 Setting the proportional gain Kp

Parameter overview

See section “Speed controller”.

3.1.13 Pole position identification

Description

For synchronous motors, the pole position identification determines its electricalpole position, that is required for the field-oriented control. Generally, the electricalpole position is provided from a mechanically adjusted encoder with absolute infor-mation. In this case, pole position identification is not required. For the followingencoder properties, pole position identification is not required:

� Absolute encoder (e.g. EnDat)

� Encoder with C/D track and pole pair number � 8

� Hall sensor

� Resolver with a multiple integer ratio between the motor pole pair number andthe encoder pole pair number

� Incremental encoder with a multiple integer ratio between the motor pole pairnumber and the encoder pulse number

The pole position identification is used for:

� Determining the pole position (p1982 = 1)

� Determining the angular commutation offset during commissioning (p1990 = 1)

� Plausibility check for encoders with absolute information (p1982 = 2)