A dynamic model of the machine subjected to control must be known in order to understand and design vector controlled drives. Due to the fact that every good control has to face any possible change of the plant, it could be said that the dynamic model of the machine could be just a good approximation of the real plant.
Nevertheless, the model should incorporate all the important dynamic effects occurring during both steady-state and transient operations. Furthermore, it should be valid for any changes in the inverter’s supply such as voltages or currents.
Nevertheless, the model should incorporate all the important dynamic effects occurring during both steady-state and transient operations. Furthermore, it should be valid for any changes in the inverter’s supply such as voltages or currents.
Such a model can be obtained by means of either the space vector phasor theory or two-axis theory of electrical machines. Despite the compactness and the simplicity of the space phasor theory, both methods are actually close and both methods will be explained.
For simplicity, fig (3-1) shows the induction motor considered which has the following assumptions:
· Symmetrical two-pole, three phase windings.
· The slotting effects are neglected.
· The permeability of the iron parts is infinite.
· The flux density is radial in the air gap.
· Iron losses are neglected.
· The stator and the rotor windings are simplified as a single, multi-turn full pitch coil situated on the two sides of the air gap.
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