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AC Voltage Regulator Circuit Schematic Diagram

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LESSON 8: SINGLE-PHASE AC VOLTAGE REGULATION

Article code: MD 23 - 08

Introduce:

Single-phase AC voltage regulators are used to regulate the speed of single-phase motors, regulate the temperature of furnaces, etc. Understanding the working principles and assembling single-phase AC voltage regulators is a necessary task for every electrical engineering student.

Target:

- Understand the schematic diagram of a single-phase AC voltage regulator circuit

- Present the working principle, draw the output current and pressure graphs.

- Demonstrate how to install components according to the schematic diagram

- Identify the type of components in the diagram

- Know how to check components

- Install circuit according to correct process, ensuring technical and aesthetic requirements, on time

- Use measuring tools and equipment properly

- Careful, accurate, strictly follow the process

- Ensure safety for people and equipment.

Main content:

* Concept:

Single-phase AC voltage regulation is a method of changing the output voltage in a sinusoidal source system by using thyristor gate pulses with the same frequency but the phase angle changes compared to the grid sinusoid. Thus, the thyristor conducts a part of the grid cycle. The starting point of the thyristor will change according to the control angle. But the thyristor only returns to the locked state when the current is zero. The basic parameter of phase control (PDC) is the phase opening angle α, also known as the slow-pass angle. Another parameter of the control scheme is the width of the thyristor pulse, which must ensure the widest range of PDC angle changes from the minimum output value (usually zero) corresponding to α = α max to the maximum α = 0

1. PURE RESISTIVE LOAD CASE:

Figure 8.1. Schematic diagram of AC voltage regulator circuit

1 phase using Thyristor

The circuit consists of a 1-phase sinusoidal AC voltage source u = U m sin t connected in series with the load R through a semiconductor AC switch. The AC switch consists of 2 thyristors connected in reverse parallel T1 and T2. In case of small capacity, they can be replaced by a triac.


Figure 8.2. Schematic diagram of a single-phase AC voltage regulator circuit using Triac

2. ANALYZE THE WORKING PRINCIPLE, DRAW THE CURRENT-VOLTAGE CURVE FOR LOAD R:

- Call source voltage: u = 2 U.sin t

In which: U and are respectively the effective value and angular frequency of the source voltage

- At t = 0, the source T does not conduct i 0 = 0, so the output voltage U 0 = 0. The voltage on the thyristor and triac is U t = U – U 0 > 0 → the thyristor is forward biased.

- At t = α, there is excitation current i g and U t > 0 → T conducts electricity, we have:

U T = 0 (voltage drop across thyristors)

U 0 = U → i 0 = U/R has a sinusoidal shape like voltage

- At t = π , U 0 = 0 , i 0 = 0 → T stops the flow.

During the negative half cycle, the voltage-current pattern is repeated but with the opposite value. Average value of the voltage across the load:

2

1

U tb =

2. U . Sin t

= . U .(cos( ​​ 1))

- Average value of current through load:

I tb = U tb /R =


2 . U .(cos( ​​ 1))

R

Figure 8.3. Graph of output voltage through load R .

- Effective value of voltage on load:


( 2 U sin )2. d

1

2 2 sin 2

2

U c = = U.


- Effective value of load current:


2 2 sin 2

2

I c = U .( )

R


- Active power supplied to the load circuit:



P = U c I c

= ( U ).(

2

R

2 2 sin 2 )

2

So by changing the angle from 0 to , one can adjust

active power from maximum value P = ( U 2 ) to 0

R

That said, even in the case of purely resistive loads, the AC grid still has to provide some reactive power.

* Steps and how to do the job :

1. EQUIPMENT, TOOLS, MATERIALS:

(Calculated for a practice session of 20 students)


TT

Equipment Type

Quantity

1

Soldering iron.

01

2

Universal board.

01

3

Clamp.

01

Maybe you are interested!

Bending pliers.

01

5

Drag

01

6

Damaged material container

01

7

Multimeter.

01

8

Oscilloscope.

01

9

Tin, rosin, wire.


10

- Components: According to the detailed component table attached


4

2. IMPLEMENTATION PROCESS:

2.1. General process:

+ How to check: use a multimeter to measure:

- Step 1: Plug the red measuring stick into the (-) socket of the meter (positive battery), plug the red measuring stick into the (+) socket of the meter (negative battery).

- Step 2: Turn the knob to the meter at the x10 (x1) resistance scale, short the two ends of the measuring rod, turn the potentiometer so that the indicator needle is at the 0Ω position.

- Step 3: Place the two ends of the measuring stick on the two diode poles as shown (Figure 1.9a) to read the value R 1

2.2. Specific process:

+ Step 1: Select components according to load requirements:

Voltage control circuit by triac with pure resistive load R, control pulse is provided by IC - TCA 785

- Introducing TCA 785:



Foot

Symbol

Function

Foot

Symbol

Function

1

OS

Grounding foot

9

R9

Sawtooth resistor

2

Q** 2

2 island output

10

C10

Sawtooth circuit capacitor

3

QU

U output

11

V11

Control voltage

4

Q *

1

1 island output

12

C12

Pulse width generator capacitor

5

VSYNC

Synchronous voltage

13

L

Short pulse, wide pulse control signal

6

I

Prohibition signal

14

Q1

Output 1

7

QZ

Output z

15

Q2

Output 2

VREF

Standard voltage

16

Vs

Power supply voltage

8


Figure 8.4. TCA785 gun shape and pin functions

+ Parameters of TCA 785:



Parameter


Minimum value

Typical value F = 50Hz

Vs = 5v

Maximum value

Unit

Consumption stream

IS

4.5

6.5

10

ghost

Control input voltage, pin11

Input impedance

V11


R11

0.2


15

V 10ma

x

V


K

Amplitude of the sawtooth Charging circuit resistance

Short side time of sawtooth pulse


I10 V10


R9 TP


10


3


80


1000

VS-2 300


AV


K

S

Prohibit input signal, pin 6 Prohibit

Allow


V6I V6H


4


3.3

3.3


2.5


VV

Pulse width output, pin13 Narrow pulse

Wide pulse


V13 H V13

L


3.5


2.5

3.5


2.5


VV

Pulse output, pin 14, 15 High level output voltage Low level output voltage Narrow pulse width Wide pulse width

V14/ 15L V14/ 15L

city

city

VS-3 0.3

20

530

VS-2.5 0.8

30

620

VS-

1.0

2

40

760

VV

S

S/n F

Control voltage Standard voltage

Control angle corresponding to electricity

standard


V ref

ref


2.8


3.1

2 x10-4


3.4

5x10 -

4


V

1/K

Sawtooth circuit Capacitor charging current


- Calculation of external elements:

Sawtooth capacitor: C10 Min = 500pF; Max = 1 F

Pulse emission time: tTr =


Capacitor charging current: I 10 =


Voltage on capacitor: V 10 =

V 11 . R 9 . C 10

V REÌ . K

V REÌ K R 9

V REÌ . K . t R 9 . C 10

TCA 785 manufactured by Siemens, used to control rectifiers, AC voltage regulators.

Adjustable angle from 0 0 to 180 0 electricity.

Main parameters of TCA 785:

+ Power supply voltage: US = 18V

+ Current consumption: IS = 10mA

+ Output current: I = 50mA

+ Sawtooth voltage: U r max = (US - 2)V

+ Resistance in the circuit to create sawtooth voltage: R 9 = 20K 500K

+ Control voltage: U 11 = -0.5 (US-2)V

+ Synchronous current: IS = 200 A

+ Capacitor: C 10 = 0.5 F

+ Output pulse frequency: f = 10 500 Hz Pinout diagram of TCA785 microchip


Figure 8.5. TCA785 functional block diagram

- Circuit diagram of TCA785 application controlling Triac in voltage regulator circuit

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