Efficient Networks S120 manual Introduction, 1RPLQDO, ZrunlqjSrlqwRi, Prwru

Vector V/f control (r0108.2 = 0) 5

5.1Introduction

The simplest solution for a control procedure is the V/f curve, whereby the stator voltage for the induction motor or synchronous motor is controlled proportionately to the stator frequency. This method has proved successful in a wide range of applications with low dynamic requirements, such as:

●Pumps and fans

●Belt drives

and other similar processes.

V/f control aims to maintain a constant flux Φ in the motor. whereby the flux is proportional to the magnetization current (Iµ) or the ratio of voltage (U) to frequency (f).

Φ ∼ Iµ ∼ V/f

The torque (M) generated by the induction motors is, in turn, proportional to the product (or, more precisely, the vector product (Φ x I)) of the flux and current.

M ∼ Φ x I

To generate as much torque as possible with a given current, the motor must function using the greatest possible constant flux. To maintain a constant flux (Φ), therefore, the voltage (V) must be changed in proportion to the frequency (f) to ensure a constant magnetization current (Iµ). V/f characteristic control is derived from these basic premises.

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Figure 5-1 Operating areas and characteristic curves for the induction motor with converter supply

Several variations of the V/f characteristic exist, which are shown in the following table:

Drive Functions	169
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4