To observe the effect of freewheeling-diode on fully controlled bridge converter with inductive load.

Experiment No.: – 07

Aim of the Experiment: –

Effect of Free-Wheeling-Diode (FWD) on SCR converter performance with inductive load.

Objective: – Understand how a FWD helps in improving voltage waveform across load despite of load being Inductive and also how the arrangement helps in fast commutating the outgoing SCR.

Apparatus Required: –

Sl. No.NameSpecificationQuantity
1Experimental KitPE trainer with INV/CON panel1 no.
2DSO/CROTwo channel1 no.
3Connecting wirePatch cord
as per required.
4Resistive load100 W bulb.1 no.
5Multimeter/Voltmeter1 no.
Table No. 7.1

Circuit Diagram: –

Fig. 7.1

Theory: –

As discussed previously, when SCR converter is subjected to Inductive load, the load voltage waveform deteriorates due to delayed commutation of outgoing SCR. The energy stored in the Inductor is also returned to supply. At times this may not be desirable. This can be avoided by connecting Free Wheeling Diode (FWD) across the converter output as shown in the fig. 7.1.

After introduction of FWD, the converter output is increases for same amount of input VA received because now the output waveform does not become negative. This improves average output voltage. (Refer fig 7.2) below.

Fig. 7.2

[If inductance enough to maintain continuous current]

Inductor dissipates it’s stored energy within load instead of returning it back to supply. This improves the input power factor and conversion efficiency, which is also a desirable effect.

Procedures: –

  1. Connect the circuit diagram as per given in fig 7.1. Observe output voltage waveforms with RL load, with and without Free wheeling diode. You may also try all the Inductors available in PE Trainer as explained earlier to observe the effect.
  2. Note down output voltage readings for different firing angles with and without FWD as per table given below.
  3. The firing pulse selector switch should be kept on 3th position for getting required gate pulses.

Note: Optimized readings may be demonstrated by using external choke from lab stock. You may try using primary windings of 230V/24V, 100VA transformers as chokes. This may be taken up as additional exercise using PE trainer.

Observation Table: –

Sl. No.Firing angle settingConverter output voltage with FWD on meterConverter output voltage without FWD on meter
1  
2  
3  
4  
5  
Table No. 7.2

Conclusion: –

Written by student

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