The document discusses a thyristor-based controlled rectifier circuit for high voltage DC transmission. It uses opto-couplers to isolate the thyristor triggering circuit from the high voltage AC input. Simulation results using Proteus show that varying the firing angle of the thyristors produces rectified outputs with different voltage levels and ripple factors. Thyristors allow controlled rectification with benefits of efficiency and reliability over uncontrolled rectification for applications like HVDC transmission.

1. Welcome to the presentation
(School of
Engineering)
American
International

2. Presented By:
Nusrat Irin Chowdhury Mary... 12-96215-3
Department of MEEE, AIUB

3. • Uncontrolled rectifiers suffer from poor output
voltage and input current ripple factor. The
uncontrolled rectification in HVDC, reduce the
efficiency by 50%.
• Thyristor in HVDC, made the system controlled and
efficient (full AC supply can be used, i.e., controlled)
• Applications of High Voltage DC transmission has
been increased, hence the necessity of related
work.
• The isolation technique is Opto-Coupling, i.e.,
isolation of HV from input to output by optical method

4. To implement a versatile and low cost power
supply system.
To implement a system capable to provide high
power where demanded.
Opto-coupling isolation triggering technique is
acceptable among all other triggering techniques,
for high power application this technique brings
safety from all other process in power supply
system.
To implement a controlled rectification in HV
application rather than uncontrolled with losses.

5. High reliability
Physically Small sized circuit with effectiveness
in costing
Capable of holding a static position (no motion)
It has an internal control circuit
Low internal power loss, hence increased
efficiency
Electrically efficient in passing signals
No feedback mechanism is used, hence simpler
method for HV transmission system
Isolation used is related to light (optical

6. • Controlled rectifiers, line commutated AC to DC power
converters, used to convert to fixed voltage, fixed
frequency AC power supply into DC output voltage.
• For building a phase controlled rectifier the diodes in the
rectifier circuit is replaced by Thyristors.
• A gate pulse must be provided with for the controlled
rectification by adjusting the delay time of the gate pulse.
• By controlling the duration of the conduction period by
varying the point at which a gate signal is applied to the
SCR, the controlled rectification is achieved.
• Controlled wave rectification converts both polarities of
the input waveform to DC and is more resourceful.

7. Some sources define silicon controlled rectifiers
and Thyristors as synonymous although Thyristor
is a rectifier circuit which contains Silicon
Controlled Rectifiers (SCR).
Thyristor is a four-layer semiconductor device,
consisting of alternating P type and N type
materials (PNPN).
Usually has three electrodes: an anode, a
cathode, and a gate (control electrode).

8. To turn-”ON” the Thyristor it
needs to inject a small trigger
pulse of current (not a
continuous current) into the
Gate, (G) terminal when the
Thyristor is in its forward
direction, that is the Anode, (A)
is positive with respect to the
Cathode, (K), for regenerative

9. One of the oldest power device, and it is employed
as power switch.
Behaves as rectifier in ON state, with a very low
forward drop, but normally in OFF state, to be in
the ON state requires a trigger on gate terminal.
In order to switch off the
SCR the voltage across it
need to be revert, from
forward to reverse bias, to
interrupt the current flowing
into it.

10. Trigger pulse need only be of a few micro-seconds in
duration
Longer the Gate pulse is applied the faster the internal
avalanche breakdown occurs, the faster the turn-”ON”
time of the Thyristor, but the maximum Gate current
must not be exceeded.
Once triggered and fully conducting, the voltage drop
across the Thyristor, Anode to Cathode, is reasonably
constant.
Once starts conduction it continues to conduct even with
no Gate signal, until the Anode current decreases below
the devices holding current, (IH) and below this value it

11. To bring the SCR from ON to OFF state, we must
reduce the current IA below the holding value IH, (a
value quite low respect to the operating current).
This is normally done by reverting the VAK voltage,
i.e., reverse biased.

12. • Thyristor circuit also called Bridge rectifier.
• Bridge rectifiers are components which have every
branch of a rectifier circuit in a single compact case.
• Bridge rectifiers can be found that operate from a few
amps to several hundred amps.
• The amount of AC voltage mixed with the rectifier's
DC output is called ripple voltage. In most cases pure
DC output is preferable, so minimizing ripple voltage is
of importance.
• If the power levels are not too great, filtering networks
may be used to reduce the amount of ripple in the

14. Pulse
Voltag
e
Sourc
e
Thyristo
rs
Rectifie
d
Output
AC Input
Pulse
Voltage
Source
Opto-
Coupler
Thyristo
rs
Pulse
Voltage
Source
VPULSE-1
Opto-
Coupler
Pulse
Voltage
Source
VPULSE-1

16. Three electrical signals are passed through the
circuit.
Pulses of Opto-coupler
Opto-coupler to Thyristors
Rectified Output after
passing Thyristors
Four different set of pulses
are fed to the coupler, which
isolate the main supply from
the single phase Thyristor
circuit to power transmission
system
Opto-coupler, then couple the
pulse to the gate terminal of the
Thyristor and help to turn it ON
Thyristors, the main part of the
circuit then converts the AC
high power to a rectified output
with the help of optical
isolation.

17. • In AC circuits the SCR can
be turned-on by the gate at
any angle α with respect to
applied voltage.
• This angle α is called the
firing angle and power
control is obtained by
varying the firing angle, or
time tα.
• For the project four sets of
the tα is used.

18. • Thyristors are Silicon Controlled Rectifier.
• The purpose of the rectifier section is to convert
the incoming AC power source to some form of
pulsating DC.
• A Silicon Controlled Rectifier is a device that
allows current to flow in one direction only. But its
rectification is controlled.
• The opto-coupling triggering techniques is used to
couple the gate pulse with the Thyristors .
• Filtering circuits is used to smooth the pulsating
DC to pure DC outputs.

19. • From the word “optics”,
meaning the science of
light and vision.
• Word “coupling”, meaning
a link or device
connecting two things.
• An Opto-Coupler is a
device used to electrically
interface between two
current- isolated systems.
It does this by way of light
transmission.

20. • The 220v ac main power supply
which is fed to the single phase
Thyristor circuit. The frequency is
50Hz.
The two pulse voltage sources VPULSE- 1 and
VPULSE- 2 supply used to trigger SCRs, which got
four set of different values with Debug times.
• 2ms and 12ms, with debug time 100ms
• 4ms and 14ms, with debug time 100ms
• 6ms and 16ms, with debug time 100ms
• 8ms and 18ms, with debug time 400ms

21. • Software based (Proteus 7.8sp2)
• Thyristor Circuit connection triggered through
opto-coupling on Proteus 7.8sp2
• Non-zero crossing opto-coupler TRIAC Pre
driver (Four pieces of Schematic Model
name M0C302X5X )
• Generic Thyristor (SCR) (Four pieces)
• Pulse voltage source (VPULSE- 1, 2)
• Sine wave AC voltage source (VSINE)
• Analog Resistor Primitive
• Oscilloscope (Virtual Instruments Mode)
• Proteus 7.8sp2 for
Simulation.

22. Designing in the
virtual world
Start,
pause,
stop

23. • The observation is done for two different keys:
 Two different sets of values of two pulse voltage
sources VPULSE- 1 and VPULSE- 2
 Sets of Debug times (mentioned in above).
The oscilloscope view of rectified four wave shapes is
shown:

24. Points of interest in the analysis were:
• Waveforms and characteristic values (average, RMS,
ripple etc.) of the rectified voltage and current.
• Influence of the load (resistor only) on the rectified
voltage.
• Harmonic content in the output.
• Voltage of the power electronic devices used in the
rectifier circuit.
• Reaction of the rectifier circuit upon the ac network the
fundamental components, harmonics, ripples etc.
• Rectifier control aspects (controlled rectifiers).

25. Calculation for four different set of pulse voltage sources
(VPULSE- 1 and VPULSE- 2) and from the calculation the
ripple values are also calculated. The calculated parameters:
• RMS (effective) value of f(FRMS)
• Average (DC) value of f(Fav)
• Form factor of f(fFF)
• Ripple of f(fR)
• Ripple factor of f(fRF)
• Fundamental component of f(F1)
• Kth harmonic component of f(FK)
• Distortion factor of f(DF)
• Total Harmonic Distortion of f(THD)

26. As with the increasing the firing times in VPULSE-
1 and VPULSE- 2, the ripple factors are increasing
which is unwanted, the filtering circuits can be
used in purpose to reduce ripples from output.
In contrast the RMS and average values, form
factors and ripples are decreasing.
The fundamental components of fourier series for
0 to 10msec of duration is 0. The other parameters
i.e., for the different triggering timing the
fundamental components is non zero. The 1st, 3rd,
5th harmonics were calculated.

27. Average values of the rectified outputs were calculated
• Fav = 0 (for 0 to 10msec)
• Fav = 0.621Vm (for 2 to 12msec)
• Fav = 0.575Vm (for 4 to 14msec)
• Fav = 0.505Vm (for 6 to 16msec)
• Fav = 0.415Vm (for 8 to 18msec)

28. • Phase control of the signals
• For Switching of Electronic devices
• Triggering the IC's and different timing circuits
• Used as controlled Rectifier.
Which summaries
• Accuracy
• Flexible
• Increasing Consistency
• Space Efficient
• Maximize Safety
• Saving cost

29. Achieved environmental, speed, and reliability specifications which
their electro-mechanical counterparts cannot fulfill
In high voltages and currents transmission
Control alternating currents to DC
Control elements for phase fired controllers.
Large amounts of power can be switched or controlled using a
small triggering current or voltage.
Used in motor speed controls, light dimmers, pressure-control
systems, and liquid-level regulators
In fluorescent lighting. Standard conventional and circular
fluorescent lamps with filaments can be ignited easily and much
more quickly by using thyristors instead of the mechanical starter
switch
Solid state thyristors are more reliable.