A frequency converter rectifies AC voltage from mains into DC voltage, after which this DC voltage is converted into a AC current with a variable amplitude and

frequency.

The motor is supplied with variable voltage / current and frequency, which enables infinitely variable speed control of three-phased, standard AC motors and

permanent magnet synchronous motors.

3.2.2 AF-650 GP Controls

The frequency converter is capable of controlling either the speed or the torque on the motor shaft. Setting par. H-40 Configuration Mode determines the type of

control.

Speed control:

There are two types of speed control:

•

Speed open loop control which does not require any feedback from motor (sensorless).

•

Speed closed loop PID control requires a speed feedback to an input. A properly optimised speed closed loop control will have higher accuracy than a

speed open loop control.

Selects which input to use as speed PID feedback in par. PI-00 Speed PID Feedback Source.

Torque control:

The torque control function is used in applications where the torque on motor output shaft is controlling the application as tension control. Torque control can

be selected in par. H-40, either in Advanced Vector Control open loop [4] or Flux control closed loop with motor speed feedback [2]. Torque setting is done by

setting an analog, digital or bus controlled reference. When running torque control it is recommended to make a full Auto tune procedure as the correct motor

data are of high importance for optimal performance.

•

Closed loop in Flux mode with encoder feedback offers superior performance in all four quadrants and at all motor speeds.

•

Open loop in Advanced Vector Control mode. The function is used in mechanical robust applications, but the accuracy is limited. Open loop torque

function works basically only in one speed direction. The torque is calculated on basic of current measurement internal in the frequency converter. See

Application Example Torque open Loop

Speed / torque reference:

The reference to these controls can either be a single refrence or be the sum of various references including relatively scaled references. The handling of references

is explained in detail later in this section.

AF-650 GP Design Guide

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