Shahid Beheshti University
Project Title:
Simulation of AC voltage controller to three phase AC
Course Name: Power Electronics 2
Bachelor Degree: MS
Producer: Torab Karim
English
Introduction :
An ac-to-ac converter usually converts alternating input voltage by means of
control circuits and power switches to a suitable voltage for the consumer,
typically changing the amplitude, frequency or phase at the output and making
the consumer usable. In this project, a simple three-phase type converter
with the purpose of controlling its output amplitude is investigated and
simulated by the MATLAB Simulink program and evaluated for voltage and
current and unwanted voltage and current harmonics.
Ι. AC to AC converters
An AC / AC converter usually receives the electrical power from an AC system
and converts it to DC AND THEN TO another AC form for the consumer. This
transformer may vary the amplitude or frequency or phase level. These
converters can be adapted to the single-phase and three-phase power as a
requirements. Converters that control the output voltage at a constant
frequency and equal to the input are known as ac voltage regulators. In this
type of converter, the output voltage can be controlled with two metods.
A: Phase control with a pair of thyristor (or trayak) and natural commutation
B: On / Off control with forced commutation with swichs (GTOs), (IGBTs),
(MCTs) etc.
The main applications of these types of controllers are lighting control,
speed control of multi-phase induction motors and temperature control of
loads etc.
The main applications of these types of controllers are lighting control,
speed control of multi-phase induction motors and temperature control of
loads etc…
1-1: Three Phase AC / AC Voltage Controller
As we know, you can control the AC voltage of
both sides using the power swichs (Thyristor,
Opacity, GTO, ...).
Different combinations are applicable to
alternating voltage controllers of threephase ,type of triangle or star depending on
the position of the swichs in the power
circui as figurs1
Figure 1: Different combinations of three
phase AC controllers
2: Simulation Circuit Diagram:
This controller requires six thyristors, each pair being parallel and
inverted.
They are placed on a phase between the load and the source and are marked
with T1; T'1; T2; T'2; T3; T'3 since the controller is all control. We must
have a fire pulse thyristor for each pair. Six pulse generator blocks are
used, the parameters of which are set for the required fire angle and
conduction period.
For example, for command T1 in generator pulse (PG1) is fire angle a = 30
and its pair T'1 must be switched on after T1 is switched off
And a delay should also be taken to ensure it is switched off. Equal to
command time T'1 = 30 + 180 (and for the other phases the same principle
applies), but the phase difference of each phase is increased to a angl
T’2=30+120+ 180 , T’3=30+240+ 180 T2=30+120
T’30=30+2240+180
Pure ohmic loads and 10 ohms are considered and oscilloscopes 1, 2 and 3 are
used to represent the pulse waveforms, voltages and currents
2-1: state a = 30
Depending on the commands and the fig of the voltage and current waves (4-9),
there are always two or three thyristors always on and in directionality. The
shape of the charge and the voltage of the charge are almost sinusoidal but
with slices
Figure: 4 waveforms VAN, VBN; VI (VAB) and I