4.2. DC motors and DC generators

DC machines can be used as DC motors or DC generators. The difference between the motor and generator is the power flow direction. The equivalent circuit of DC motors and DC generators is similar to each other, but the direction of the current flow of the DC motors is opposite to the direction in DC generators [2].

In a DC machine, the induced voltage is directly proportional to the flux and the speed of rotation of the machine. The magnetomotive field force is produced by field current, which in turn produces flux along with its magnetization curve.

As long as the field current is proportional to the magnetomotive field force and the induced voltage is proportional to the produced flux, it is usual to present the magnetization curve as a plot of EA-induced voltage with respect to the current of the field for a constant speed ω0.

#### 4.2.1. Types of DC motors


In cumulative compounded motor, the current flows into the dots of both field coils. The resulting magnetomotive forces add to produce a larger total magnetomotive force.

In differential compounded motor, the current flows into the dot on one of the field coils and out of the dot of the other field coil, the resulting magnetomotive forces subtract.

## 4.2.2. Types of DC generators


e. Differentially compounded generator: is a DC generator in which both the shunt and the series fields are available, but their effects are subtracted.

#### 4.3. Implementation on GUI MATLAB

The torque on the armature of a real machine is

opposite to the direction in DC generators [2].

turn produces flux along with its magnetization curve.

4.2. DC motors and DC generators

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4.2.1. Types of DC motors

separate voltage supply.

4.2.2. Types of DC generators

armature terminals of the motor.

connected in series with the armature circuit.

supplies the field flux to the DC generator.

to produce the field flux to the DC generator.

produce the field flux to the DC generator.

series fields are available, and their effects are added.

Tind <sup>¼</sup> ZP 2πa

DC machines can be used as DC motors or DC generators. The difference between the motor and generator is the power flow direction. The equivalent circuit of DC motors and DC generators is similar to each other, but the direction of the current flow of the DC motors is

In a DC machine, the induced voltage is directly proportional to the flux and the speed of rotation of the machine. The magnetomotive field force is produced by field current, which in

As long as the field current is proportional to the magnetomotive field force and the induced voltage is proportional to the produced flux, it is usual to present the magnetization curve as a plot of EA-induced voltage with respect to the current of the field for a constant speed ω0.

a. Separately excited DC motor: is a DC motor where the field circuit is supplied by a

b. Shunt DC motor: is a DC motor whose field circuit gets its power directly across the

c. Series DC motor: is a DC motor where the field windings consist of few turns that are

d. Compounded DC motor: is a motor that consists of both a shunt and a series field. It

In cumulative compounded motor, the current flows into the dots of both field coils. The resulting magnetomotive forces add to produce a larger total magnetomotive force.

In differential compounded motor, the current flows into the dot on one of the field coils and out of the dot of the other field coil, the resulting magnetomotive forces subtract.

a. Separately excited generator: a separate power source, independent of the generator,

b. Shunt generator: the field circuit is connected directly to the generator terminals in order

c. Series generator: the field circuit is connected in series with the generator armature to

d. Cumulatively compounded generator: is a DC generator in which both the shunt and the

consists of two types: cumulative and differential compounded DC motor.

φIA ð29Þ

A graphical user interface is implemented for DC machine with types of generators and motors. The first GUI will obtain the armature resistance for any DC machine (Figure 12).

The user will determine the type of winding and enter the inputs which are pole number. Coil numbers and turn numbers with the plex and resistance per turn then calculate results. The armature resistance (RA) is expressed by

$$\text{RA} = \frac{\text{Turns} \times \frac{\text{coils}}{\text{current path}} \times \text{(resistance perturn)}}{\text{current path}} \tag{30}$$

The results will be displayed with armature resistance included. This value will be installed in the other part of the graphical user interface for DC generators and DC motors.

The graphical user interface for the types of DC generators and DC motors is shown in Figure 13.


Figure 12. GUI to determine the armature resistance of DC machines.


Figure 13. Graphical user interface for the types of DC motors and DC generators.

The user will choose the type of DC generator/motor and enter the corresponding parameters. Push buttons are available to load and save the data, calculate the armature resistance, and quit the program. Results will be displayed with the terminal characteristic and torque speed characteristics (Figures 14 and 15).

The equivalent circuit of the type of motor or generator will be displayed after calculating the result.

Figure 14. DC motor terminal characteristics.

Figure 15. DC generator terminal characteristics.

#### 5. Induction machines

The user will choose the type of DC generator/motor and enter the corresponding parameters. Push buttons are available to load and save the data, calculate the armature resistance, and quit the program. Results will be displayed with the terminal characteristic and torque speed

The equivalent circuit of the type of motor or generator will be displayed after calculating the result.

characteristics (Figures 14 and 15).

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Figure 14. DC motor terminal characteristics.

#### 5.1. Induction motors and induction generators

An induction machine is a machine with only a continuous set of amortisseur windings. They are induction machine because the voltage of the rotor is induced in the rotor winding instead of being physically connected with wires. To run the machine, it does not require a DC field current. Induction machines can be used as either generators or motors. Induction machines are not used as generators except in some special applications due to their disadvantages. Therefore, induction machines are most of the time referred to as induction motors [2].

After applying a three-phase voltage to the stator, current flows into the stator which produces magnetic field that rotates in a counterclockwise direction. The rotation speed of the magnetic field is expressed by

$$m\_{\rm sys} = \frac{120f\_{\rm se}}{P} \tag{31}$$

The relative motion of magnetic field and rotor is defined with two terms, which are


$$n\_{slip} = n\_{sync} - n\_m \tag{32}$$

$$s = \frac{n\_{\text{slip}}}{n\_{\text{sync}}} \times 100\% \Rightarrow s = \frac{n\_{\text{sync}} - n\_m}{n\_{\text{sync}}} \times 100\% \tag{33}$$

Note that the rotor turns at s = 0, whereas at s = 1, the rotor is stationary.

#### 5.2. The equivalent circuit of an induction motor

The equivalent circuit of an induction motor is similar to that of the transformer, with a difference between the magnetization curve of the transformer and induction machine (Figures 16 and 17).

#### 5.3. Implementation on GUI MATLAB

A graphical user interface is implemented on MATLAB for induction machines (Figure 18).

The user has to enter details related to the induction machine:


As we noticed, the double-cage design, when compared to the single-cage rotor, has a high starting torque with smaller maximum torque and a slightly higher slip in the normal operating range.

machines are not used as generators except in some special applications due to their disadvantages. Therefore, induction machines are most of the time referred to as induction

After applying a three-phase voltage to the stator, current flows into the stator which produces magnetic field that rotates in a counterclockwise direction. The rotation speed of the magnetic

nsys <sup>¼</sup> <sup>120</sup><sup>f</sup> se

b. Slip: It is the relative speed expressed as ratio of slip speed to synchronous speed in a

� <sup>100</sup>% ) <sup>s</sup> <sup>¼</sup> nsync � nm

The equivalent circuit of an induction motor is similar to that of the transformer, with a difference between the magnetization curve of the transformer and induction machine

A graphical user interface is implemented on MATLAB for induction machines (Figure 18).

1. In this part the user can calculate and display the result of induction machine torque

As we noticed, the double-cage design, when compared to the single-cage rotor, has a high starting torque with smaller maximum torque and a slightly higher slip in the normal operat-

nsync

The relative motion of magnetic field and rotor is defined with two terms, which are

a. Slip speed: It is the synchronous speed minus rotor speed.

<sup>s</sup> <sup>¼</sup> nslip nsync

The user has to enter details related to the induction machine:

2. Single- and double-cage rotor characteristic (Figure 20).

5.2. The equivalent circuit of an induction motor

5.3. Implementation on GUI MATLAB

characteristics (Figure 19).

Note that the rotor turns at s = 0, whereas at s = 1, the rotor is stationary.

<sup>P</sup> <sup>ð</sup>31<sup>Þ</sup>

� 100% ð33Þ

nslip ¼ nsync � nm ð32Þ

motors [2].

field is expressed by

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percentage basis.

(Figures 16 and 17).

ing range.

Figure 16. The transformer model of an induction motor, with rotor and stator connected by an ideal transformer of turn ratio aeff.

Figure 17. The magnetization curve of an induction motor compared to that of a transformer.


Figure 18. Graphical user interface for three-phase induction machine.

Figure 19. Equivalent circuit and torque speed characteristic.

Figure 20. Single- and double-cage rotor characteristic.
