The Dc Motor Speed Control Methods Engineering Essay

ABSTRACT

This paper describes the Matlab and simulink converts into actuality of the DC motor speed control methods, namely field resistance, armature resistance control methods and armature voltage, and feedback control system for DC motor drives and this paper describes mathematical modelling, simulation of DC motor system using computer simulations Matlab and simulink, by this system response to change various parameters like system stability, disturbances, analysis and optimization of model parameters with respect to the quality of control. If simulation techniques are used for determining the control parameters a simulation model is necessary, which has to be constructed from the analytical model.

INTRODUCTION

DC Motor is an electrical motor and it most commonly used in an electrical device for easy to drive the instruments, steel rolling mills, electric cranes, and robotic manipulators due to precise, wide, simple, and continuous control characteristics. To control the speed of low power DC Motor rheostatic armature control method were used. The basic parts of the DC motor are- axle, rotor (armature), stator, commutator, field magnet, and brushes. In the geometry of brushes, commutator contacts, and rotor windings are arranged in such a manner so that when power is applied then polarities of the energized winding and the stator magnets are misaligned and the rotor will start to rotate until it is almost aligned with the stator’s field magnets. When the rotor reaches to alignment, the brushes move to next commutator contacts, and energize the next winding.

There are variable types of DC Motor available in market with the good and bad qualities. Bad quality means lag in efficiency. To recover or stop this kind efficiency problem controller is introduce in the system.

Brushed DC motors are most widely used in applications and its ranging from toys to push-button adjustable car seats. Brushed DC (BDC) motors are inexpensive but easy to drive.

Brushed DC motors are easily available in all size and shape with the wide range from large-scale industrial models to small motors for light applications (such as 12 V DC motors).

.

BDC motors are most commonly used in easy to drive, with variable speed and high start-up torque applications.

OBJECTIVE

The Fig.1 shows the analogues electrical circuit.

MODELLING

The circuit which was given is drawn in the Matlab by using simulink. In the circuit diagram the flow of current

BLOCK DIAGRAM

Figure shows the block diagram of DC motor

TRANSFER FUNCTION

K/{(Ls+R)(Js+f)+K2}

±

1/s

Vapp

Fig 4.1. Transfer Function

STATE SPACE MODEL

As we know that,

V- .…. (1)

….. (2)

Substituting equation (2) in (1)

……. (3)

….… (4)

……. (5)

Substituting (5) in (4)

– ……… (6)

Differentiating (6), we get

……….. (7)

Putting (3) in (7), we get

……… (8)

Now

………… (9)

Substituting (9) in (8), we get

We know that x=Ax + Bu

Y=Cx + Du

X=

The State Space Model represents by the linear equation and it is written as.

x= Ax + Bu

y = Cx + Du

Below figure shows the state space model (Calculation is in appendix)

Figure 5.1 State Space Model

PHYSICAL SYSTEM

Consider a DC Motor, in this electrical circuit of the armature and free body diagram of rotor are shown in figure below.

http://zone.ni.com/cms/images/devzone/tut/mpm-2-motor1.gif

Fixture: – DC Motor is a common actuator in control systems.

Brushed DC Motor fundamentals

A Brushed DC Motor consists of stationary fixed permanent magnets i.e. stator, a rotating electromagnetic i.e. rotor and flux, which is concentrated by metal. Rotor rotate by the attraction of the opposite poles and repulsion of the like poles, it cause to generate torque and torque acts on rotor and then make it turn. As the rotor start to rotate or turn then fixed brushes make and breaks the contact in such a way that with the rotating segments (commutation). The rotor coil of the brushed motor energized and de-energized in such a way so that the rotor start to turns. By transferring the power to the motor, current generate in rotor coils and therefore the north and south poles are reversed and because of the motor change the direction. From the Strength of the magnetic field, speed and torque of the motor depend

Figure (1) Brushed DC Motor

PRINCIPLE OPERATION

Construction and operation of the Brushed DC Motor is shown below in figure (2).for the construction of the BDC motor always the same components are required i.e. Stator, rotor, commutator and brush.

Figure (2) Simple two-pole brushed DC Motor

Stator

The rotor surrounded by the stationary magnetic field which is generated by the stator and this filed is generated by the permanent magnet or electromagnetic winding. On the construction of the stator, different types of BDC distinguish.

Rotor

Rotor is also known as an armature and it is made up of one or more windings. Magnetic field is produce when they energized. When the opposite pole of the magnetic poles, attract to each other which is generated by the stator, and causing the rotor to turns. The opposite poles are always attracting to each other. As the motor turns, the windings are being constantly energized. This deviation of the field in the rotor is called as an armature.

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Brushes and commutator

There is no requirement of controller in BDC to switch current in motor winding. The commutation winding of the BDC motor is done mechanically. Reside on the axel of rotor there is a segmented copper sleeves called commutator. Carbon brushes slides over the commutator coming in a contact with the different segments of the commutator as the motor starts to turn. When the voltage is applied across the brushes of the motor then dynamic magnetic field is generated inside the motor. Brushes and commutator are the most important parts of the BDC motor that are most prone to wear because they are the sliding part to each other.

SPEED CONTROL

The Speed of a DC Motor is directly proportional to the voltage. By using the digital controller voltage can be control and to generate the average voltage pulse-width modulated (PWM) signal is used. In motor there is a motor winding which acts as a low pass filter so PWM develop a suitable current in the motor winding.

ADVANTAGES

Cheap in price because low cost of construction.

Extend a life by replacing a brush.

Inexpensive motor and simple control.

Speed/Torque is normal at high speed.

On fixed speed no control is required, Controller is required only at variable speed in this condition same controller can be used.

DISADVANTAGES

Maintenance is required for brushed DC Motor because of brush.

If the brush friction increases, reduce the useful torque.

Heat dissipation is poor because of internal rotor construction.

Speed range is limited because of the mechanical limitation on brushes.

Life is also shorter.

Noise is generated due to brush.

Application examples:

moving toys, fans, printers, robots, electric bikes, -doors, -windows, -sun roofs, -seats, mixers, food processors, can openers, blenders, vacuum cleaners, toothbrushes, razors, coffee grinders, etc.

Physical Parameters

Moment of inertia of the motor (J) = 9.89 E-7 kg Nm s/rad

Damping ratio of the mechanical system (b) = 5.84E-7 Nm s/rad

Electromotive force or motor constant (K=Ke=Kt) = 0.008 Nm/-w

Electric resistance (R) = 0.80 ohms

Electric inductance (L) = 0.00041H

Friction coefficient, f

Input (V): Source Voltage

Output (theta): position of shaft

the rotor and shaft are assumed to be rigid

CONCLUSION

Brushed DC motors are very simple to use and easy to control,

which makes them a short design-in item. PIC

microcontrollers, especially those with CCP or ECCP

modules are ideally suited for driving BDC motors.

Refference

Circuit Diagram for DC Motor Control by A. Collins

http://www.nxp.com/documents/application_note/AN10513.pdf

http://ww1.microchip.com/downloads/en/AppNotes/00905a.pdf

http://www.orientalmotor.com/MotionControl101/AC-brushless-brushed-motors.html

http://ww1.microchip.com/downloads/en/AppNotes/00885a.pdf

http://www.dynetic.com/brushless%20vs%20brushed.htm

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