Morning everyone, my name is Rachid and I am a student in electrical engineering. I am currently working for a school project on an extinction circuit for an SCR. The diagram can be seen below.
The first diagram represent the real system. The blue arrows indicate the charging path for the capacitor. It will be charged through the diode till its voltage reaches the Input voltage value Vin. The red Arrow indicate the discharging path when SCR2is triggered. The output is a typical RL parallel load.
The SCR1 is the main SCR that feed the load and the SCR2 is used to activate the extinction circuit in order to apply a reverse voltage at the terminals of the main SCR1 during a sufficient time (in my case 200us) so that the main SCR turns off.
To ease the calculations, I made the assumption that the voltage is constant during 200us as this time is smaller than the periode of the input voltage.
In transient mode, the equation which describes the behavior of the circuit during the discharge phase through the SCR is the following:
According to Kirchhoff's voltage low: Vin + Uc - Vout = 0 so Vout = Vin+Uc For current low , we have the following relation Ir + IL = Ic
At the end I got the differential equation :
** Note: at the beginning of the discharge, i. e. when the control signal is sent to SCR 2 to block SCR 1, Uc(0) = Vin and Ic(0)= 0
The solution is as follow:
As i've got this equation, I would like to know which efficient method i can use to determine the value of the Capacitor so that the capacitor voltage reach 0 after 200us when SCR2 is triggered.
the main problem is that the term capacity is found in all parts of the Uc equation, so it is difficult to isolate
The parameters are as follow:
-Vin = 230 V peak
-R = 0.8816 Ohm
-L = 0.00579 H
-C = ?
-tq to turn off the SCRs is 200us
Thank you for any help i can get
The first diagram represent the real system. The blue arrows indicate the charging path for the capacitor. It will be charged through the diode till its voltage reaches the Input voltage value Vin. The red Arrow indicate the discharging path when SCR2is triggered. The output is a typical RL parallel load.
The SCR1 is the main SCR that feed the load and the SCR2 is used to activate the extinction circuit in order to apply a reverse voltage at the terminals of the main SCR1 during a sufficient time (in my case 200us) so that the main SCR turns off.
To ease the calculations, I made the assumption that the voltage is constant during 200us as this time is smaller than the periode of the input voltage.
In transient mode, the equation which describes the behavior of the circuit during the discharge phase through the SCR is the following:
According to Kirchhoff's voltage low: Vin + Uc - Vout = 0 so Vout = Vin+Uc For current low , we have the following relation Ir + IL = Ic
At the end I got the differential equation :
** Note: at the beginning of the discharge, i. e. when the control signal is sent to SCR 2 to block SCR 1, Uc(0) = Vin and Ic(0)= 0
The solution is as follow:
As i've got this equation, I would like to know which efficient method i can use to determine the value of the Capacitor so that the capacitor voltage reach 0 after 200us when SCR2 is triggered.
the main problem is that the term capacity is found in all parts of the Uc equation, so it is difficult to isolate
The parameters are as follow:
-Vin = 230 V peak
-R = 0.8816 Ohm
-L = 0.00579 H
-C = ?
-tq to turn off the SCRs is 200us
Thank you for any help i can get