A permanent magnet DC motor is a synchronous motor powered by a DC electric source via an integrated inverter that produces an AC current which drives the motor (Zhu et al., 1993). It has the stator and armature as the main features. The permanent DC motor has several characteristics that enable it to run. The electrical characteristics Torque Vs. Amature current (Ta-Ia).Torque is directly proportional to the product of armature current and field flux. The field winding is connected in series with the armature in DC series motors. Thus Torque increases with the square of armature current (Hanselman, 2003). The general equation for the electrical characteristics is;
Va-Ia Ra-La d/dt ia kv a=0.
It also has the mechanical characteristic that states that when the speed is high, then torque is low (N-Ta). The general equation for mechanical characteristics can be combined to;
kt ia- Jd/dt a-Ba-TL=0.
The dynamic model of the magnet is made up of three materials. The materials used in a PMDC model are of three types, Alnicos, Rare earths and the ferrites. The Alnicos have strong magnetic properties, high residual flux density and a low coercive magnetic intensity in that it can withstand high temperatures of uto1000 degrees Celsius. The alnico is used where high voltage and low current is required. Ferrites are difficult to demagnetize and they are not corrosive. They are used in microwaves, refrigerators and air conditioners. Rare earths are the strongest types of permanent magnets. They are very expensive. They are made up of samarium cobalt and neodymium-iron-boron; they have high residual flux and high coercive magnetic intensity. When a carrying conductor comes into contact with the magnetic field, then a mechanical force will be experienced in the direction of the force. The amateur inside the magnetic field rotates in the direction of the force that has been generated and each conductor experiences the mechanical force. The compilation of the forces experienced in the amature gives a torque force that rotates it (Krishnan, 2009).
Where; Vis the voltage, I is the current passing through the circuit, R is the resistance inside the motor and E is the emf.
Equation that involving the DC motor as it runs
F= q (E + v B). Where E denotes the electric field, B represents the magnetic field; q is a charge moving with a speed v in the space.
Hanselman, D. C. (2003). Brushless permanent magnet motor design. The Writers' Collective.
Pillay, P., & Krishnan, R. (1989). Modeling, simulation, and analysis of permanent-magnet motor drives. II. The brushless DC motor drive. IEEE transactions on Industry applications, 25(2), 274-279.
Zhu, Z. Q., & Howe, D. (1993). Instantaneous magnetic field distribution in brushless permanent magnet DC motors. II. Armature-reaction field. IEEE Transactions on Magnetics, 29(1), 136-142.
Krishnan, R. (2009). Permanent magnet synchronous and brushless DC motor drives. CRC press.
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