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Gate Pulse Triggering of Single Phase Thyristor Circuit through Opto-Coupling

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Gate Pulse Triggering of Single Phase Thyristor Circuit through Opto-Coupling

  1. 1. Welcome to the presentation (School of Engineering) American International
  2. 2. Presented By: Nusrat Irin Chowdhury Mary... 12-96215-3 Department of MEEE, AIUB
  3. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
  13. 13. 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
  14. 14. 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.
  15. 15. • 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.
  16. 16. • 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.
  17. 17. • 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.
  18. 18. • 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
  19. 19. • 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.
  20. 20. Designing in the virtual world Start, pause, stop
  21. 21. • 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:
  22. 22. 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).
  23. 23. 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)
  24. 24. 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.
  25. 25. 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)
  26. 26. • 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
  27. 27. 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.

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