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Abstract

The DC to AC converters is known as

investors. The function of an inverter is to change a DC

input voltage to a symmetrical AC output voltage with the

desired magnitude and frequency. Both the output voltage

and frequency can be fixed or variable. The Inverter 3-

phase frequency variable and opto-coupled interface

basically consists of two parts: the control circuit and the

circuit Force. The control circuit consists of a clock circuit

tone burst type, consisting of two circuits It integrated

cascade, where the frequency is varied by a pot (variable

resistor); which enable two cascaded flip-flop where the

pulses are 180 out of phase reach the opto couplers, there

are connected to the power circuit. Power circuit

arrangement comprises a six-transistor diodecorresponding to an inverter phase fed a 12 volt DC

source. This is where the resistive loads are connected and

/ or Inductive either delta or star; should be noted that the

supply of this equipment is alternating (AC), but the

power integrated circuits is DC so they were designed and

implemented rectified sources for effect..

I ndex Termsinverter, igbt, SPWM, three phase, PID

contol, harmonics, phase, AC voltage, DC.

I.

INTRODUCTIONTHe drive maintains constant engine speed, to change the

speed you need to use a mechanical clutch to change the motor

poles or as in most industries frequency to the motor to change

speed is used, the speed change is possible do so through a

change of voltage at the motor or by placing a variable resistor

in the rotor, but these methods have serious drawbacks in the

engine and they are very expensive, efficient way to change

the motor speed through change of frequency at a time should

be accompanied by a voltage change not to saturate the

magnetic flux, so it is now so widespread use of the inverter

and voltage: most of these devices require a three-phase

power; but they are very expensive equipment and therefore if

you do not have sufficient resources to purchase it will benecessary to search for similar equipment becomes the only

option; The objective of this project is the realization of a

frequency and voltage at very low cost and easy accessibility

to the recommended elements for its realization; thus

benefiting the small businessman.

.

Rectifier circuit: this stage consists of a diode bridge rectifier

or thyristor, for transforming the alternating current.

Intermediate circuit: This step consists of an LC circuit for

smoothing the ripple waveInvestor: at this stage the voltage intermediate circuit delivers

a voltage which is variable as it should at this stage frequency

IGBT pulse generated by the variation are used.

Control Circuit: This circuit is going to be used to control

switching and IGBT switching is also possible to control

variables such as temperature and voltage peaks

Current circuits are controlled by the pulse generating PWM

(Pulse Width Modulation), the alternating current passing

through a bridge rectifier and reaches de4spues LC circuit

which smoothes the ripple also helps reduce coil harmonics

which significantly increases the efficiency of the motor,

another option is to use the DC coils which generate a large

voltage across which can have a negative influence on theengine performance, the IGBTs working at frequencies

between 2 and 16 KHz when the frequency of the IGBT is

very high it dissipates more heat in the circuit and faults in the

IGBT, also more often a decrease is obtained in noise but

significantly reduces engine efficiency, must take precautions

to IGBTs as these generate some peaks in voltage depending

on cable length or very high frequencies which are detrimental

to the long term engine, so it is necessary to electrically isolate

the circuitry to protect the control stage in which sensors are

or microcontrollers that operate at low voltages and currents,

some manufacturers to avoid these drawbacks do not permit a

greater connection to 7 m.

II.

DESCRIPTION

To construct a frequency and voltage is necessary to divide the

system into several blocks; This conversion is voltage and

variable frequency voltage has a step to facilitate mounting in

many ways so it is advisable before mounting the circuit

simulating each of the stages to ensure each. The steps for the

project are described below:

Rectifier stage: This stage will feed the circuit with twosources, the first of 5V connect to the control part; ie the stage

that controls the frequency, shooting and Gap waves being

generated in the IGBT, also at this stage we must ensure 9 V

in the coupling step, the power that results from the phase

network not controlled the which rectifies the three-phase

lines turning AC current into DC current, then the current

passes through filters that add up to the total 2100uF at 500V,

the current flowing in the circuit is determined by the diode

source; in our case the current is 12 mA, which can cause

problems in the plate to fix this current is necessary to install 2

mA current sources each, so it is possible to neutralize the

VARIABLE FREQUENCY DRIVE

Diego Aragn Sotelo, 42091003


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stream exiting the diode in the inverters in the industry today

diodes are replaced by SCR because these devices support

higher current and voltage is variable.

Frequency Control: In this step, an LM555 device will need to

generate a pulse or stable clock is chosen, the LM555 for his

versatility and why programming is only electronic ie

according to the value of the resistors used in the

configuration as an oscillator, to calculate the necessaryfrequency must take into account that the motor moves in 6

step therefore minimum frequency and maximum frequency

calculated to be multiplied by 6 to thereby obtain the

frequency range leaving the LM555. To calculate the

maximum frequency is necessary to set the knob to the

smallest ohmic value, once there is no load on the electrolytic

capacitor is discharged across the frequency is out of the

output pin of the LM555, and thus by mathematical

calculations relating the time to the frequency is calculated

and the frequency may work on each of the phases. If you

want greater precision is necessary to replace the resistance of

LM 555 for precision potentiometer

And firing phase control: It is now necessary to use a shift

register of 8 bits, the NOR gates LM555 and 6, the shift

register will scan then 6 bits, when the control circuit sends

the signal device it restarts automatically and be in a QF

e4stado returns to the initial Q0 and again make another sweep

recording when it detects another signal; while 6 gates

generate the gap and maintain the constant voltage to drive the

inputs of the coupling step, the oscillator LM555 is

responsible for generating the data to the log entry. This way

you can create a shot every 62.7 ms which is ideal for smooth

engine operation this control it is called 6-step drive

COUPLING STEP:

Fig. 1

At this stage there are 3 output handlers receiving the high

signal low, each generator provides 2 outputs for this circuit is

necessary to have a low voltage sensor in each of the outputs,

to ensure that the voltage at the top not change as this can

cause failures motor voltage is carried to a man who compares

this voltage load 0.5Vy there is a comparator signal that

inhibits signal to each of the outputs, this gives a TTL signal

and the output according to the output give a diagnosis about

the signal. There is an internal amplifier that generates an

analog signal that is proportional to the frequency Vss.

Low Voltage Protection: Set by a condition that Vss is less

than 8.9V for the circuit to operate normally and when the

potential difference of 9.3 V greater off all outputs.

Over current protection: In case of short circuit is advisable toturn the 6 outputs, for it ITRIP protection resistor, which is

installed on the low side is used is compared.

BLOCK DIAGRAM SYSTEM

In the block diagram shown he circuit consists of five

stages, including feeding it through the three-phase network,

the detailed explanation of each stage is developed where thedevelopment of each stage separately explain, to serve thus the

suggestions of the activity guide. At the moment it is

mentioned that the three-phase AC voltage is converted to AC

through the inverter, the output of the inverter is filtered by a

full wave based on elements SCR power to rectify its output

signal, from there is a circuit of frequency variation, they are

precisely the variations in frequency which must control

generally the speed of the induction motor, considering that

there is a direct relationship between the frequency inverter

output circuit frequency and supply voltage of the induction

motor, the fourth stage involved in the design is a control step,

which should handle the trip command IGBT comprising the

step

power or gain of the circuit, which links the stages of

filtering and frequency variation with engine power itself.

III.

RESULTS

To calculate the minimum and maximum frequency, it must

be borne in mind that this type of drive is six steps, and

therefore the minimum frequency and the maximum desired

frequency inverter must be multiplied by 6, to determine the


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value of the frequency that must exist in the output of the 555,

in our case the values are:

minimum frequency = 5 Hz

maximum frequency = 67 Hz

6 HZ * 6 = 30 Hz

67 Hz * 6 = 402 Hz

The frequency to be obtained at the output of 555 is at least

30 Hz and a maximum of 402 Hz.

What time is known T = 1/f

Therefore:

T min = 1/30 = 33,333 ms.

Tmax = 1/402 = 2,487 ms.

Estos tiempos dados incluyen los tiempos ON y OFF de la

seal, los cuales deben de ser separados en partes iguales para

as obtener un ciclo positivo y negativo idnticos:

T min = 33,333 ms / 2= 16,666 ms

T max = 2,48 m / 2 = 1,2437 ms

En esta etapa los tiempos de encendido y apagado son

aproximadamente iguales producto del diodo que se encuentra

en el paralelo a la Resistencia y al potencimetro. El tiempo se

obtiene de la siguiente formula:

T = tiempo segundos

0,69 = constante

T = 0,69 * R * C

C = capacitor value

R = depending on how often you want to calculate.

The resistance value depends on the frequency value being

calculated, bone, to calculate the maximum frequency, the

potentiometer must be at its minimum ohm value, with this

load resistance of the electrolytic capacitor decreases, causing

the frequency is maximized at the output of 555, then this

calculation only due to take the resistance of 820 ohms and a

minimum frequency, the potentiometer 10 k ohm be calculated

at the maximum value then it must add the ohmic valuemaximum resistance potentiometer. With this in mind the

calculation is as follows:

C = 2,2 uf

T = 0,69 * (820 + 10E3) * 2,2E-6

T = 16,424 ms.

T = 16,424 ms * 2= 2,489 ms

F = 1/T= 1/32,849 ms= 401,683 HZ

Desired in a process minimum frequency was 30 Hz a value of

30.44 Hz and the maximum frequency was 402 Hz and

401.683 Hz was obtained was obtained, if these values are

divided by 6 is obtained that the end frequency of the lines

would be between 5 and 66 Hz. Both values are quite close to

those originally proposed to improve the accuracy of the

desired frequency must replace the resistors for adjustment

potentiometers because with this' can achieve a value more

accurate.

Simulation.

The shape of each transistor drive waveform and these lead

lines presented below separately.

IV.

CONCLUSIONS.

The three phase supply, especially the diodes can be replaced

by the SCR, to obtain a voltage control and get more power

from the source, if this variation should increase the power of

the Resistance .

Remove the power supply of the control circuits and matingto replace it by a power zener governed by, the idea is not

having to rely on a neutral for use and thus eliminate this

source transformer, this reduces to weight, space and possible

interference from the natural magnetic field produced by this

type of transformers.

V.

REFERENCES

[1]

Quintero, Jorge. Mdulo de electrnica industrial.

(2008).Bogot. Universidad Nacional Abierta y a


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distancia-UNADW.-K. Chen, Linear Networks and

Systems. Belmont, CA: Wadsworth, 1993, pp. 123135.

[2]

J. U. Duncombe, Infrared navigationPart I: An

assessment.

[3]

High Power Converters and AC Drives, BIN WU,

IEEE.

[4] R.G. Seippel, Optoelectronics (Reston-Virginia, Prentice-

Hall, 1981).[5] M. Rashid, Electrnica de Potencia; Circuitos,

Dispositivos y Aplicaciones pp. 356

[6]

R. Boylestad, Electrnica de Circuitos pp. 155

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