Welcome to the presentation

(School of Engineering)American International

University – Bangladesh (AIUB)

Gate Pulse Triggering

of Single Phase Thyristor Circuit

throughOpto-Coupling

Project Supervisor: Amzad Ali Sarkar Assistant Professor

Faculty of Engineering, AIUB

Project External: Nafiz Ahmed ChistyAssistant Professor & Special Assistant

Faculty of Engineering, AIUB

Presented By: Nusrat Irin Chowdhury Mary... 12-96215-3

Department of MEEE, AIUB

• 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 and increasing the efficiency with revers costing.

Introduction to The Project

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.

Objectives of the Project

High reliabilityPhysically Small sized circuit with

effectiveness in costingCapable of holding a static position (no

motion)It has an internal control circuitLow internal power loss, hence increased

efficiencyElectrically efficient in passing signalsNo feedback mechanism is used, hence

simpler method for HV transmission system

Isolation used is related to light (optical isolation), its mechanism uses LED to pass the signals.

Why chosen?

• 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.

Control Rectification

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).

Thyristor

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 latching to occur.

Thyristor TURN ON and OFF Conditions

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.

Thyristor TURN ON and OFF Conditions (continued)

Thyristor cross section

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.

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 automatically turns-”OFF”.

Triggering Pulse

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.

Electrical Characteristic Curves of Thyristor

• 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 output voltage.

What is “Thyristor Circuit”?

Single and Three Phase Bridge Rectifier Circuits

Pulse Volta

geSource

Thyristors

Rectified

Output

AC Input

Pulse Voltag

eSourc

e

Opto-Coupler

Thyristors

Pulse VoltageSource

VPULSE-1

Opto-Coupler

Overview of the Project

Pulse VoltageSource

VPULSE-1

Single Phase Thyristor Circuitry schematic diagram

Overview of the ProjectSignal Flow (continued)

Three electrical signals are passed through the circuit.

Pulses of Opto-couplerOpto-coupler to ThyristorsRectified 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 systemOpto-coupler, then couple

the pulse to the gate terminal of the Thyristor and help to turn it ONThyristors, the main part of the circuit then converts the AC high power to a rectified output with the help of optical isolation.

Controlling the Signal Flow

• 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.

Phase Control

• 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.

Rectifier

• 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.

Opto-Coupler

• 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

Pulse Voltage Sources

AC main supply

• Software based (Proteus 7.8sp2)• Thyristor Circuit connection triggered

through opto-coupling on Proteus 7.8sp2

Parts of the Project

Design Part/ Simulation

• 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.

Electronic Components

SoftwareUsed

Simulation in ProteusDesigning in the

virtual world

Start, pause, stop

• 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:

Observations

1 2

3 4

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).

Analysis of Calculation

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)

Terminologies of Calculations

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.

Results from Calculations

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)

Results from Observations

(continued)

• 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

Benefits in HV Application

Application of Thyristor CircuitAchieved environmental, speed, and reliability

specifications which their electro-mechanical counterparts cannot fulfill

In high voltages and currents transmissionControl alternating currents to DCControl 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 regulatorsIn 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.

That is all about the

presentation(Thank You)