DC Machine Characteristics

Target>>>

1. Implement DC machine torque speed characteristics equations in MATLAB script file. It asks user to input data and plots speed (RPM) versus torque (Nm). Submit the .m file for evaluation and attach the screenshots of all the required plots
2. How can you distinguish between power cables and signal cables in wiring of an electric vehicle?
3. What voltage levels are considered as high & low for a battery pack of electric vehicle?

Answers>>>

1. A DC Machine is an electro-mechanical energy conversion device. There are two types of DC machines, one is -- i) DC generator and another one is known as the ii) DC motor

Matlab Code ---

We have taken 5 variables to get torque speed equation of DC machine-

Fig-DC Machine

It is a steady-state approximation of a DC machine. Since steady-state, the armature inductance (La">La) is neglected.

Now, V-- DC input voltage;

Ra-- Armature resistance;

Ia-- Armature current;

Ke-- Back EMF constant;

Kt-- Torque constant;

Eb-- Back EMF

w-- Angular speed

T-- Torque

Where, angular speed(w)= (2*3.14*linear speed(N)/60)

We know these following equation-- Eb= Ke*w.....(i)

T= Kt*Ia.....(ii)

Eb= V-Ia*Ra.....(iii) (Obtained from the shown Circuit diagram)

T=(Kt*V/Ra)-(Ke*Kt*w/Ra)

From the characteristic equation we we get the Speed vs Torque graph showing below--

From this graph we can say that speed and torque of a DC motor is invarsely proportional with each other. Eb=Ke⋅ω...(1)

T=Kt⋅Ia...(2)

Eb=V−IaRa...(3)(obtained from equivalent circuit shown)

From the above 3 equations,

T=(Kt*V/Ra)−(Ke*Kt*ω/Ra)

2. Cable type is determined by a number of factors, including current draw and temperature rise created by the current as it runs through the conductor; cable temperature rating; and as other thermal factors such as air flow, other sources of heat, etc. Power cables are those which can conduct a large ammount of current and power. This cables bear a thick outer sheath compared to ordinary Control cables. The external sheath of the Power cables with its immense strength and protection enables the cables to transfer high volume of energy without any tension or strain. These are mainly electrical cables.Cross sectional area of this type of cable is large.

Fig-- Power Cable
Whereas Signal cable can carry very less ammount of current and power. This cables send signals to control functioning of any equipment. These cables allow distribution of data or signals that have low voltage. These are mainly electronics type of cable.Cross sectional area of this type of cable are less than Power cable. Fig-- Signal Cable

From this block diagram we can get that Signal input is coming to electric power distribution controller then signal is send to motor controller and then to motor . The whole process is carried out by signal cable; mainly all electronics or digital part is connected via signal cable and power from battery to electric power distributon controller & motor is supplied by power cable; mainly all electrical large power application is connected via power cable.

3.Today's electric vehicles (EV) use a high system voltage due to the reduction of the appearing current. After a detailed investigation, three voltage levels (24 V, 48 V, 300 V) of a possible battery pack will be examined in terms of costs and technical effects. Fig-- Battery Pack

Voltage level less than 48V is considered as low and greater than 300V is considered as high level battery pack of EV.