Power Electronics Lab Experiments

Study of Single Phase Bridge Controlled Rectifier with R and RL load with and without freewheeling diode

Nov 27 2023

Aim

Study of Single Phase Bridge Controlled Rectifier with R (Lamp Load), RL (motor 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 Bridge Controlled Rectifier with Lamp Load

Single Phase Bridge Controlled Rectifier with Motor Load

Single Phase Bridge Controlled Rectifier with Motor Load with freewheeling diode

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, SCR2, SCR4 and SCR5 from SCR Assembly and to construct single phase bridge controlled rectifier configuration.
Connect cathode of SCR1 to cathode of SCR2 and connect anode of SCR4 to anode of SCR5.
Connect cathode of SCR4 to anode of SCR1 and connect cathode of SCR5 to anode of SCR2.
Connect Line Terminal (L) from single phase supply to anode of SCR1 or cathode of SCR4 and connect neutral terminal (N) to anode of SCR2 or cathode of SCR5.
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 SCR4 and SCR5.
Connect gate pulse G1 at gate (G) of SCR1 and connect K1 at cathode of SCR1 from ramp comparator firing circuit.
Connect gate pulse G2 at gate (G) of SCR5 and connect K2 at cathode of SCR5 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.
Connect gate pulse G4 at gate (G) of SCR4 and connect K4 at cathode of SCR4 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.
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	207	1.667	226.66	239
60	155.3	151	3.33	206.3	209
108	51.76	55.9	6	127.33	128
120	71.54	58.8	6.667	101.69	120

RL load without freewheeling diode:

Firing angle(α)	V_avg(Theoretical)	V_avg(Practical)	Time Period(ms)	V_rms(Theoretical)	V_rms(Practical)	β(ms)	β(degrees)
60	140.68	150	3.33	209	208	11.5	207
108	57.12	68.7	6	130.95	140	11.3	203.4
120	37.34	22	6.66	109.34	99.8	11.7	210.6
150	-0.547	-8.24	8.33	56.039	44.2	11.7	210.6

RL load with freewheeling diode:

Firing angle(α)	V_avg(Theoretical)	V_avg(Practical)	Time Period(ms)	V_rms(Theoretical)	V_rms(Practical)
60	155.3	148	3 .33	206.3	207
108	71.54	83.9	6	127.32	143
120	51.76	44	6.67	101.69	99.7
150	13.87	4.97	8.33	39.05	38.3

Equations:

V_{0 =}V _m= Vm/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(Cosα- Cosβ)

V_rms= = V _s[1/π[(β-α) + sin2α-sin2β/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 for single phase full wave bridge converter was observed.