Four Quadrant operation of PMDC motor using Chopper controller.

Objective:

1. Design and Development of converter, inverter model using MATLAB simulation.
2. Design and development of DC machine drive MATLAB model for speed control.
3. Measurement of different parameters experimentally such as speed torque current of DC motor drive.

Apparatus Required:

Sl. No	Name	Specification	Remarks
01	Four Quadrant Chopper DC-DC converter Kit		01 nos.
02	Single phase PMDC motor with spring load	0.5HP, 180 V, 2.1 A 1500 rpm	01 nos.
03	CRO		01 nos.
04	Tachometer	Digital Type	01 nos.

Circuit Diagram:

Theory: 

                  Apart from using AC to DC line commutated converters, an alternate way to get a variable DC voltage is the use of DC-to-DC converters as choppers. As the name suggests the chopper will convert a fixed DC voltage into a variable DC voltage. The chopper fed DC motor is one application where both the speed control application as well as the regenerative braking action can be performed most efficiently. The speed control of a DC motor over a wide range is possible with rectifiers as well as with DC choppers. The latter is preferred for the following reasons. Better control performance with a rectifier requires an increasing number of phases, which involves increased cost, both for the transformer as well as the rectifier. Moreover, high chopper frequency provides a smoother output and also helps in reducing the region of discontinuous conduction in the speed –torque plane. Chopper based DC drives provide improved performance with less plicated circuits. The PIC microcontroller is used to control a IGBT based four quadrant chopper control DC motor, has a frequency of 50 Hz.

The choppers are also divided on the basics of the quadrant of their operation. single quadrant, two quadrant & four quadrant operation. Four Quadrant Operation of any drives or DC Motor means that the machine operates in four quadrants. They are Forward Braking, Forward motoring, Reverse motoring and Reverse braking. A motor operates in two modes – Motoring and Braking. A motor drive capable of operating in both directions of rotation and of producing both motoring and regeneration is called a Four Quadrant variable speed drive. In motoring mode, the machine works as a motor and converts the electrical energy into mechanical energy, supporting its motion. In braking mode, the machine works as a generator and converts mechanical energy into electrical energy and as a result, it opposes the motion. The Motor can work in both, forward and reverse directions, i.e., in motoring and braking operations.

Procedures:

1. Ensure pot P1 is in zero (middle position) & there is no link for power connection.
2. Connect 12 pin/8 pin cable from the motor to the socket on the panel.
3. Keep Sw2 in an upward position. Switch ON the main supply. LEDs V1, V2 & V3 should glow.
4. Connect CRO across test points TP2 & ground and move the P1 in clockwise direction. At TP2 one should get a chopping waveform with variable PWM & at TP4 you should get approximately 5-volt DC supply. No O/P appears at TP1 & TP3.
5. When pot P1 is moved in anticlockwise position w.r.t zero, then at TP1 one should get chopping waveform & 5-volt DC at TP3. No O/P at TP2 & TP4.
6. When switch Sw2 is thrown in a downward position, with pot P1 in forward direction, at TP1 chopped waveform should appear & no O/P at TP2, TP3 & TP4. likewise with Pot P1 in anticlockwise direction (reverse direction), TP2 should give chopped waveform while TP1, TP3 & TP4 gives no O/P. After observing the waveform, switch Sw2 to an upward (normal) position with Pot P1 at zero middle position.
7. Now place a link for power circuit you can move the pot slowly in forward (clockwise direction) to observe that the motor moves in forward direction & speed varies as pulse width is increased. You may load the motor with simple loading arrangement. Note the current direction. Now when switch Sw2 is thrown in a downward position, the motor goes in regenerative mode & stored energy is returned to power supply & reverse current flows as indicated by the ammeter. The voltage across the filter condenser increases. If there is load on the motor, the braking action is quick. This is the 3rd quadrant operation. If the system is turned OFF with Sw2 in upward direction, there is no regenerative braking & the motor takes a long time to come to halt. The pulley on the motor is used to store mechanical energy. 
8. In step (6) you may also observe waveforms at TP1, TP2, TP3 & TP4 with respect to ground. Throw switch Sw2 in upward position & bring pot P1 to zero position.
9.  Now you can move Pot P1 in an anticlockwise direction. Repeat all the steps in step (6) above to observe the motor operation 2nd & 4th quadrant. 
10. You may also observe the waveform at TP1, TP2, TP3 & TP4.
11. When Sw3 is in downward position lamp load is connected & there is no question of stored energy & no possibility of regenerative braking. Only lamp load intensity changes.
12. In forward /reverse motoring mode, you may observe the output waveform CRO across on the dedicated test point provided.

Observation Table: Clockwise with No-Load 

Sl. No	Output Voltage (V) in Volts.	Load current (I) in amps.	Speed (N) in RPM	W1 in Kg.	W2 in Kg.	W=(W1-W2) in Kg.	Torque (T) in N-m
1
2
3
4
5
6

Observation Table: Counter-Clockwise with No-Load 

Sl. No	Output Voltage (V) in Volts.	Load current (I) in amps.		Speed (N) in RPM	W1 in Kg.	W2 in Kg.	W=(W1-W2) in Kg.	Torque (T) in N-m
1
2
3
4
5
6

Conclusion: Written by students.