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The flexible control of DC motor has been donated in the extensive use of DC motor in the era of industry, as the increasing usage of semiconductor power converter units. The speed control of DC motor is very sophisticated and specific. The speed of DC motor has been controlled by controlling the armature voltage by using thyristors. The armature voltage is controlled by using the different types of AC to DC semiconductor converters such as half wave converter, semi converter and full wave converter by using thyristor-diodes. This paper shows the experimental comparative analysis of the DC motor speed control by using the different power converter topologies performed at the Quaid-E-Awam University of Engineering Sciences and Technology, Nawabshah lab.

The DC motors are widely used because of their simplicity in their control action. The smartness of the DC motor is its control up to the wide range. Dc Machine can be controlled by armature voltage control, armature voltage controlled by AC-DC converters [

A single phase half wave thyristor based converter which is used to control the DC motor is shown in

Single phase semi wave thyristor based converter is shown in

A single phase full wave thyristor based converter is shown in

The armature voltage converters may be half, semi and full converter and works on positive and negative voltage from first quadrant to fourth quadrant.

When a DC supply is applied to the armature of the dc motor with its field excited by a dc supply, torque is developed in the armature due to the contact between the axial current carrying conductors on the rotor and radial magnetic flux is produced by the stator. If V is the applied voltage applied to the armature terminal of the motor, and E is the internally developed rotational e.m.f. The resistance and inductance of the complete armature are represented by Ra and La as shown in

Under driving conditions, the rotational e.m.f. E always opposes the applied voltage V, and for this reason it is referred to as “back emf” for current to be forced in to motor, V must be greater than E, the armature circuit voltage equation being given by

The last term in Equation (1) denotes the inductive voltage drop due to armature self-inductance. This voltage is proportional to rate of change of current, so under steady state conditions (i.e. when the current is constant), the term will be zero and can be overlooked. Under steady state-condition, the armature current I is constant and Equation (1) simplifies to

The motor back emf is given by

where

Z is number of armature conductors.

N is speed in rpm.

A is number of parallel paths in armature.

Here Z, P, A are fixed for a particular machine after wounded. Therefore for a given DC machine

where

The torque developed by armature is given by

where,

From expression (2)

Substituting Equation (10) in Equation (9), we get

Substituting Equation (9) in Equation (11), we get

Rearranging the above equations, we get

The above expression gives the relationship between speed and torque for DC motors. Speed-current rela-

tionship can be obtained if

low

where

a) Resistance added to armature circuit.

When resistance is inserted in armature circuit, the speed drop

b) Terminal voltage (Armature voltage).

Reducing the armature voltage V of the motor reduces the motor speed.

c) Field Flux (or field voltage).

Reducing field voltage V of the motor reduces the flux, and the motor speed increases.

Controlling Speed by regulating armature voltage

A common method of controlling speed is to adjust the armature voltage. This method is very efficient, stable and is simple to implement. The circuit diagram shown in

When armature voltage is reduced no load speed is also reduced, the armature voltage does not affect the speed drop

Therefor characteristics are shown as

The speed control analysis of the DC motor by using different power converters such as half wave, semi converter and full wave converter. This analysis is purely based on the experimental analysis of power converters by applying different torques on the DC motor in QUEST University Nawabshah Sindh Pakistan laboratory. The applied torque changing from 0 to 2 Nm (mechanical) load, to analyze the speed of the DC motor by using the different power converters, the model picture of DC motor with patching diagram shown in

The results of the speed-torque characteristics of DC motor on the single phase half wave converter, semi converter and full wave converter shown in following

In

In

S. NO. | Half Wave Speed (rpm) | Torque (N.m) | Armature Voltage |
---|---|---|---|

1 | 3106 | 0 | 237 |

2 | 2890 | 0.2 | 222 |

3 | 2594 | 0.4 | 201 |

4 | 2304 | 0.6 | 183.6 |

5 | 2118 | 0.8 | 167.6 |

6 | 1908 | 1 | 154.6 |

7 | 1757 | 1.2 | 143 |

8 | 1667 | 1.4 | 133 |

9 | 1467 | 1.6 | 125 |

10 | 1300 | 1.8 | 121 |

11 | 1200 | 2 | 117 |

S. No. | Semi Wave Speed (rpm) | Torque (N.m) | Armature Voltage | |
---|---|---|---|---|

1 | 2660 | 0 | 207 | |

2 | 2630 | 0.2 | 200 | |

3 | 2610 | 0.4 | 199 | |

4 | 2580 | 0.6 | 197 | |

5 | 2540 | 0.8 | 194 | |

6 | 2530 | 1 | 189 | |

7 | 2450 | 1.2 | 180 | |

8 | 2350 | 1.4 | 170 | |

9 | 2250 | 1.6 | 168 | |

10 | 2150 | 1.8 | 164 | |

11 | 2050 | 2 | 160 | |

rent will effect on linearity of DC motor torque but comparatively it is observed that in semi converter has less discontinuous current and smaller non-linearity.

In

It is comparatively shown in

This paper deals with the experimental and comparative analysis of AC/DC power semiconductor converters (i.e. half wave converter, semi converter and full wave converter) with study of speed-torque characteristic of the DC motor for armature current and torque mode. This study is performed in the laboratory of the Quaid-E-Awam

S. No. | Full Wave Speed (rpm) | Torque (N.m) | Armature Voltage |
---|---|---|---|

1 | 3517 | 0 | 269 |

2 | 3296 | 0.2 | 251 |

3 | 3159 | 0.4 | 237 |

4 | 2943 | 0.6 | 230 |

5 | 2800 | 0.8 | 216 |

6 | 2646 | 1 | 208 |

7 | 2499 | 1.2 | 198 |

8 | 2380 | 1.4 | 112 |

9 | 2287 | 1.6 | 184 |

10 | 2200 | 1.8 | 170 |

11 | 2000 | 2 | 160 |

S.No. | Half Wave Speed (rpm) | Full Wave Speed (rpm) | Semi Speed (rpm) | Torque Speed (rpm) |
---|---|---|---|---|

1 | 3106 | 3517 | 2660 | 0 |

2 | 2890 | 3296 | 2630 | 0.2 |

3 | 2594 | 3159 | 2610 | 0.4 |

4 | 2304 | 2943 | 2580 | 0.6 |

5 | 2118 | 2800 | 2540 | 0.8 |

6 | 1908 | 2646 | 2530 | 1 |

7 | 1757 | 2499 | 2450 | 1.2 |

8 | 1667 | 2380 | 2350 | 1.4 |

9 | 1467 | 2287 | 2250 | 1.6 |

10 | 1300 | 2200 | 2150 | 1.8 |

11 | 1200 | 2000 | 2050 | 2 |

University of Engineering Sciences and Technology, Nawabshah, Sindh, Pakistan. The DC motor has been taken for experimental test on various torque (mechanical load) applied on DC motor ranging from 0 to 2 Nm; it has been observed that discontinuous in armature current due to each converter. This inferior property of power converters will effect on DC motor torque, which is not acceptable for heavy load. It is concluded that the semi power converter has less non linearity in the torque due to small discontinuity of the armature current as comparing with half wave and full wave power converters.

Abdul Khalique Junejo,Ghullam Mustafa Bhutto,Munawar Ayaz Memon,Ehsan Ali Buriro, (2015) Lab Based Analysis of Speed Control of DC Motor by Using Different Semiconductor Power Converters. Open Access Library Journal,02,1-11. doi: 10.4236/oalib.1101530