Power Electronics Lab Experiments

Study of Single Phase Semi-converter with R and RL load with and without freewheeling diode

Nov 27 2023

Aim

Study of Single Phase Semi-converter (Common Cathode Configuration) with resistive load (Lamp load), RL load with and without freewheeling diode.

Apparatus Required:

High Voltage Power Electronics Lab
2mm Patch Cord
4mm Patch Cords
Product Tutorials

Circuit Diagram

Single Phase Semi-converter (Com mon Cathode Configuration) with Lamp Load

Single Phase Semi-converter (Common Cathode Configuration) with Motor Load

Single Phase Semi-converter (Effect of Freewheeling Diode) with Motor Load

Procedure:

Make sure that there is no connection on the Work Bench initially.

Switch on the three phase MCB of back panel.
Red, Yellow and Blue indicator glow at front panel.
Connect +12V, +5V and ground (GND) and connect 18-0-18 at ramp comparator firing circuit from single phase low voltage power supply.
Use SCR1 and SCR2 from SCR Assembly and use diode D1 and diode D2 from Diode Assembly and to construct single phase semi-converter common cathode configuration.
Connect cathode of SCR1 to cathode of SCR2 and connect anode of diode D1 to anode of diode D2
Connect Line Terminal (L) from single phase supply to anode of SCR1 or cathode of diode D1 and connect neutral terminal (N) to anode of SCR2 or cathode of diode D2.
Connect the one terminal of load from Load Assembly to common cathode terminal of SCR1 and SCR2 and other terminal of load is connect to common anode terminal of diode D1 and diode D2.
Connect gate pulse G1 at gate (G) of SCR1 and connect K1 at cathode of SCR1 from ramp comparator firing circuit.
Connect gate pulse G3 at gate (G) of SCR2 and connect K3 at cathode of SCR2 from ramp comparator firing circuit.
Verify the connections before switch on the MCB of single phase supply.
Connect BNC to BNC cable at CH1 of oscilloscope to output of Power Scope A.
Switch of ATT of A is x 100 position and switch of coupling of A is DC position.
Connect input of Power Scope A to the load.
Connect the Lamp at the Load.
Switch on MCB of Single Phase Supply and observe the output waveform of load terminals on the oscilloscope.
Connect the DC Voltmeter at the load and measure the output DC voltage across the load.
Observe the output waveform at the load as shown in figure.

Observation table: R load:

Firing angle(α)	V_avg(Theoretical)	V_avg(Practical)	Time Period(ms)	V_rms(Theoretical)	V_rms(Practical)
30	193.2	193	1.667	226.66	234
40	182.54	179	2.2	222.34	227
88.2	106.79	123	4.9	166.03	184

RL load without freewheeling diode:

Firing angle(α)	V_avg(Theoretical)	V_avg(Practical)	Time Period(ms)	V_rms(Theoretical)	V_rms(Practical)
68.4	141.65	150	3.8	196.37	207
104.4	80.95	91.5	5.8	136.47	154
126	45.34	54.1	7	92.57	101

RL load with freewheeling diode:

Firing angle(α)	V_avg(Theoretical)	V_avg(Practical)	Time Period(ms)	V_rms(Theoretical)	V_rms(Practical)
68.4	141.65	151	3.8	196.37	206
102.6	80.95	97.7	5.7	136.47	160
124.2	45.34	73.3	6.9	92.57	134

Equations:

V_{0 =}V _m/π(1+cos α)

V_rms= = V _s[1/π[(π-α) + sin2α/2]] ^1/2

RL load with and without freewheeling diode:

V₀ = V_m/π(1 + Cosα)

V_rms= = V _s[1/π[(';π'-α) + sin2α/2]] ^1/2

Theoretical calculations:

Experimental Waveforms:

R load:

RL load:

RL load with freewheeling diode:

Conclusion: By varying the firing angle control potentiometer of ramp comparator firing circuit, output voltage across the loads, their waveform was observed.