Figure 1. Half waveSCR rectifier circuit
The simplest controlled rectifier uses a single SCR, to produce variable voltage d.c. from fixed voltage a.c. mains. The circuit arrangement is shown in figure 1.
Operating principles for Resistive load
In the above arrangement, we have:
vs = Vm sin ωt = 0.707 V sin ωt = 0.707V
where Vm and V are the maximum and rms (effective) value of the supply voltage, respectively.
We note that from oldest article, the SCR is turned-on in the positive half-cycle (forward biased), some-time after supply voltage increase from zero, by the application of a positive gate pulse with delay angle a. For the negative half-cycle, the SCR is reverse biased and cannot switch on. In the other hand, the negative cycle will be blocked by SCR.
If we increase the delay angle (also called firing angle), the smaller average load voltage will be applied to the load. Otherwise, the higher average output voltage will be feed by the load if we decrease a. Note that: The average load voltage (Vd) from SCR half wave rectifier is found by calculating the area under the voltage curve then dividing by the length of the base. For any delay angle a, the average load voltage is represented by
Vd = (Vm/π) (1+ cos a)
To make a clear understanding of SCR half wave rectifier, please see figure 2. In this figure, we show the SCR voltage waveforms for two different delay angles.
Figure 2. dc output voltage which form by SCR half wave rectifier for two different firing (1)
Case example:(taken from ref 1)
A thyristor half-wave controlled converter has a supply voltage of 220V at 50Hz and a load resistance of 100 Ω. What are the average values of load voltage and current when the firing delay angle is (a) 30°(b) 90°?
(a) a =30°
Vd = (Vm/π) (1+ cos a)
Vd = (0.707.220/ π) (1+ cos 30°) = …. (please help me! Using your calculator)
(b) a =90°
Vd = (Vm/π) (1+ cos a)
Vd = (0.707.220/ π) (1+ cos 90°) = …. V
In summary, the average voltage or dc output voltage which form by SCR half wave rectifier is varied by adjusting the firing angle,a.
Interesting? Download this in pdf format.
References:
[1] Fewson. D(1998). Introduction to Power Electronics. Oxford University Press, Inc.
[2] Aripriharta, 2005-2012. Lecture Note. Power Electronics & Drives. Unpublished-for Education Only. State University of Malang, Faculty of Engineering, Departement of Electrical Engineering. (The original note, written in Bahasa Indonesia)
In the above arrangement, we have:
vs = Vm sin ωt = 0.707 V sin ωt = 0.707V
where Vm and V are the maximum and rms (effective) value of the supply voltage, respectively.
We note that from oldest article, the SCR is turned-on in the positive half-cycle (forward biased), some-time after supply voltage increase from zero, by the application of a positive gate pulse with delay angle a. For the negative half-cycle, the SCR is reverse biased and cannot switch on. In the other hand, the negative cycle will be blocked by SCR.
If we increase the delay angle (also called firing angle), the smaller average load voltage will be applied to the load. Otherwise, the higher average output voltage will be feed by the load if we decrease a. Note that: The average load voltage (Vd) from SCR half wave rectifier is found by calculating the area under the voltage curve then dividing by the length of the base. For any delay angle a, the average load voltage is represented by
Vd = (Vm/π) (1+ cos a)
To make a clear understanding of SCR half wave rectifier, please see figure 2. In this figure, we show the SCR voltage waveforms for two different delay angles.
Figure 2. dc output voltage which form by SCR half wave rectifier for two different firing (1)
Case example:(taken from ref 1)
A thyristor half-wave controlled converter has a supply voltage of 220V at 50Hz and a load resistance of 100 Ω. What are the average values of load voltage and current when the firing delay angle is (a) 30°(b) 90°?
(a) a =30°
Vd = (Vm/π) (1+ cos a)
Vd = (0.707.220/ π) (1+ cos 30°) = …. (please help me! Using your calculator)
(b) a =90°
Vd = (Vm/π) (1+ cos a)
Vd = (0.707.220/ π) (1+ cos 90°) = …. V
In summary, the average voltage or dc output voltage which form by SCR half wave rectifier is varied by adjusting the firing angle,a.
Interesting? Download this in pdf format.
References:
[1] Fewson. D(1998). Introduction to Power Electronics. Oxford University Press, Inc.
[2] Aripriharta, 2005-2012. Lecture Note. Power Electronics & Drives. Unpublished-for Education Only. State University of Malang, Faculty of Engineering, Departement of Electrical Engineering. (The original note, written in Bahasa Indonesia)