Electrical Machine

By electrical machine, here we mean a generator or motor. 

We shall discuss the operation of machine

as a generator and motor.

Operation of Machine as a Generator (Conversion of Mechanical Energy into

Electric Energy)

A coil is placed in a constant stationary magnetic field. Let it be rotated in clockwise direction at an angular velocity of Z radians per second by some outside driving mechanical torque Tm. 

The coil sides cut the magnetic field (or the flux linking with coil changes) and emf (e) is induced in the coil.

The coil is connected to an external load resistor R, therefore current (i) flows through the coil and external load resistor. The direction of flow of current in the coil is marked in Fig. 

When current flows through the coil conductors, they produce their own magnetic field. 

If the coil circuit is not closed, no current would flow through the coil and hence no electromagnetic torque will be developed (i.e., Te = 0), under such a condition the opposition is only due to frictional torque (neglecting iron losses). 

Operation of Machine as a Motor

Now consider a coil placed in the constant stationary field. The coil is connected to a battery.

The current i flows through the coil conductors in the direction shown in Fig.

Current carrying conductors produce axis of magnetic field Fr in the direction as marked.

The rotor field Fr tries to come in line with the main field Fm. Thus, electromagnetic torque is developed on the coil in anticlockwise direction. 

The coil is free to rotate, therefore, it starts rotating in anticlockwise direction (say at w rad/sec).

When the coil rotates in anticlockwise direction, flux is cut by the conductors (coil sides).

The emf is induced in them in the direction.

Electrical Machine Applications 

Electric motors are found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives. They may be powered by direct current or by alternating current which leads to the two main classifications: AC motors and DC motors.

Electric machines are essential systems in electric vehicles and are widely used in other applications. In particular, permanent magnet direct current (PMDC) motors have been extensively employed in industrial applications such as electric vehicles and battery-powered devices such as wheelchairs, power tools, guided vehicles, welding equipment, X-ray and tomographic systems, and computer numerical control (CNC) machines. 

PMDC motors are physically smaller and lighter for a given power rating than induction motors. The unique features of PMDC motors, including their high torque production at lower speed and flexibility in design, make them preferred choices in automotive transmissions, gear systems, lower-power traction utility, and other field. 

For efficient torque/speed control, thermal management, motor-condition monitoring, and fault diagnosis of PMDC motors, it is essential that their characteristics be captured in real-time operations. This is a system identification problem that can be carried out by using standard identification methods.