Four Quadrant Chopper Fed DC Motor Drive

Aim:

To study the operation of Multi quadrant Chopper based DC Drive.

Learning Objectives:

• To study the operation of Multi quadrant Chopper based DC Drive.

• To study Chopper fed DC drive.

• To study Multi quadrant operations of a Chopper

Apparatus:

• Experimental kit

• DSO/CRO (Unearthed)

• Multimeter

• Patch cords and DSO probes

PreTest

Theory:

There are three basic types of dc-dc converter circuits, termed as buck, boost and buck-boost. In all of these circuits, a power device is used as a switch.

Four Quadrant Chopper are widely used for motion-control equipment in the automation industry. Because of significant development of power switching devices, switching frequencies of 10–20 kHz are easily attainable.

Chopper Fed DC Drive:

                                                         Fig 1: Chopper Fed DC Drive

• The basic circuit arrangement for a single-phase converter-fed separately excited DC motor is shown in Figure.

• It uses two different converters for Armature and Field control.

• By controlling Duty Cycle of the Chopper converter we can control armature voltage and field voltages can be separately given by Controlled / Uncontrolled rectifier to adjust field voltage.

• If the armature circuit of a dc motor is connected to the output of a single-phase controlled rectifier, the armature voltage can be varied by varying the Duty cycle of the Chopper. By controlling Armature voltage we can control speed of a DC motor.

Circuit Description

Class E Chopper

Class E is four quadrant chopper. It operates in four quadrants of Vo-Io. The output current as well as voltage both can take positive or negative values. The first quadrant is forward motoring. The output voltage and current both are positive. The Third quadrant is reverse motoring. This means the motor rotates in the opposite direction compared to first quadrant.

Fig shows the circuit diagram of four quadrant chopper having transistor switches. Whenever S1 and S2 conducts the chopper operates in the first Quadrant. Vo and Io both are positive. When S3 and S4 conduct Vo and Io both are negative. The chopper operates in the third Quadrants.

Four Quadrant chopper has the capability to operate in all four quadrants. Hence it is used in reversible dc drives. The braking is regenerative. Hence four quadrant chopper drives are highly efficient.

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Procedure:

Use Unearthed DSO or Power scope

1. Switch on the power supply.

2. Observe control block O/P & vary the pot, observe the effect.

3. Observe the current waveform across shunt.

4. Measure the voltage across motor.

5. Change the Forward or Reverse position of switch and observe the effect.

6. Tabulate the results.

7. Draw the graph of Speed Vs output voltage for Forward and Reverse

Experiment Procedure

Observations:

Forward Motoring

Sr.No	Ton	T	Duty Cycle D=Ton/T	O/P Voltage	Speed(RPM)

Reverse Motoring

Sr.No	Ton	T	Duty Cycle D=Ton/T	O/P Voltage	Speed(RPM)