PPT of Power Electronics for electrical engineering.pptx

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1. Different Methods of Thyristor Submitted To: Engr. Nazim Siddique Submitted By: Mirza Hassan 17093322-034 Talha Shehzad 17093322-026

2. What is Thyristor ? A thyristor is a solid-state semiconductor device with four layers of alternating P- and N-type materials. It acts exclusively as a switch, conducting when the gate receives a current trigger, and continuing to conduct until the voltage across the device is reversed biased, or until the voltage is removed.

3. What is the use of a thyristor ? A thyristor , or silicon controlled rectifier (SCR), is a solid-state component which is used in order to switch and control electric current flow. Due to the robustness of thyristors , they are often used in high current flow applications.

4. Temperature triggering: Temperature triggering of SCRs or thyristors occurs as the voltage across the junction J2 and any leakage current may raise the temperature of the junction. The increase in temperature further increases the temperature which will in turn increase the leakage current. This cumulative process may be sufficient to trigger the SCR, although it tends to only occur when the device temperature is high.

5. Light triggering: This form of SCR triggering or firing is often used with high voltage systems . LIGHT Triggering is the method to turn ON the SCR. It is triggered by passing a beam of light of particular wavelength on the SCR. When current in the SCR is below the holding current the device operates in forward Turn OFF region so the photons of light increase the energy level of the atoms inside SCR. So, the flow of electrons increases and current increases beyond latching current hence the SCR is turned ON . To enable the light triggering to take place, light is often directed to the correct point in the thyristor / SCR using optical fibre . Once the light exceeds a certain intensity, switching occurs. An SCR of this type is often referred to as a Light-activated SCR or LASCR.

6. Gate Control Methods This is most common and efficient method to turn ON the SCR. When the SCR is forward biased, a sufficient voltage at the gate terminal injects some electrons into the junction J2. This result the breakdown of junction J2 even at the voltage lower than the VBO. In gate triggering method, a positive voltage applied between the gate and the cathode terminals. We can use three types of gate signals to turn On the SCR. DC signal AC signal P ulse signal

7. DC Signal In this triggering, a sufficient DC voltage is applied between the gate and cathode terminals in such a way that the gate is made positive with respect to the cathode. The gate current drives the SCR into conduction mode. In this, a continuous gate signal is applied at the gate and hence causes the internal power dissipation. AC Signal This is the most commonly used method for AC applications where the SCR is employed for such applications as a switching device. With the proper isolation between the power and control circuit, the SCR is triggered by the phase-shift AC voltage derived from the main supply.

8. Pulse Signal  In this method, gate is supplied with single pulse or a train of pulses. The main advantage of this method is that gate drive is discontinuous or doesn’t need continuous pulses to turn the SCR and hence gate losses are reduced in greater amount by applying single or periodically appearing pulses.