AN1112 Datasheet PDF - ST Microelectronics
Part Number | AN1112 | |
Description | THREE-PHASE MOTOR CONTROL | |
Manufacturers | ST Microelectronics | |
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APPLICATION NOTE
Three-Phase Motor Control by using ST52x301
Authors: M. Di Guardo, G. Grasso, M. Lo Presti
Introduction
Induction motors with squirrel-cage are widely used in industrial environments because of their low cost
and rotors rugged construction.
The induction motor is a simple and robust machine, but its control migth be a complex task. When ma-
naged directly from the line voltage, the motor operates at nearly a constant speed. To obtain speed and
torque variations, it is necessary to modify both the voltage and the frequency, by using an electronic
www.DataSchoenevt4eUr.tceormmust be used to perform this operation.
The best way to run the motor is by using a PWM sine-wave modulation, but in many applications this
can result very expensive for the complex implementability.
The six-step modulation (square wave) is a low-cost solution that allows to run the motor at various
speeds.
The aim of this application is to describe how ST52x301 can easily work to obtain frequency and voltage
variations in the Inverter Driver and how to perform a closed loop control.
Speed control by varying stator frequency and voltage
The rotor speed can be controlled by varying the frequency of the stator voltage F. This is possible by
varying Vs in a linear proportion to F.
Varying the stator frequency and voltage is the preferred technique in most variable-speed induction mo-
tor drive applications. This technique is known as V/F=constant.
As displayed in figure 1, for a small value of slip frequency (Fsl= Fs-Fr) and for fixed flux values, a linear
relationship between Torque T and Fsl (slip) takes place at any frequency F.
Fig . 1 Torque Speed Characteristics
φ = constant
January 1999
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Three-Phase Motor Control by using ST52x301
By using this method the line to line r. m. s. voltage is about:
V(rms) = 0.78*Vd*d
where d is the PWM duty cycle
In the following figure is shown the schematic block of the ST52x301 board that allows to reproduce a
six step modulation. The main parts of this system are the microcontroller, the circuit utilized to provide
the bridge control signals (U*, V*, W* and U*, V*, W*) and the three-phase inverter driver.
Fig . 8 - System Schematic block
www.DataSheet4U.com
ST52T301
Ref. A/D PWM
Timer
Digital
I/O
U
V
W
U*
V*
W*
+
U*
V* W*
U* V* W*
-
R
SM
T
Speed
® 5/ 22
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Part DetailsOn this page, you can learn information such as the schematic, equivalent, pinout, replacement, circuit, and manual for AN1112 electronic component. |
Information | Total 22 Pages | |
Link URL | [ Copy URL to Clipboard ] | |
Download | [ AN1112.PDF Datasheet ] |
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