A new state-equation of the induction motor will be presented. The state-equation of induction motors is indispensable in design of vector control. In the vector control, high performance is realized by decoupling control. In case of the conventional state-equation, physical operation of the induction motor is difficult to understand. This is because, in the conventional state-equation, the physical meaning of the coupled terms are not easily discerned since the branches of the summing point don't have voltage dimension.
In order to design the current controller, the transfer function of the motor after the decoupling control is used. If the conventional state-equation is used, this transfer function becomes the second-order including the rotor resistance. Therefore, it becomes difficult to design the current controller and the fluctuation of the transfer function occurs by temperature change of the rotor resistance.
To overcome these problems, a new state-equation in matrix form which enables the physical meaning of the coupling terms to be easily discernable, is proposed. In this equation, all branches of the summing point have voltage dimension, and thus the equation enables easy understanding of the physical operation of the machine. Since the matrix theory is used, the existence of coupling between the magnetizing-axis and torque-axis becomes clear, and it is easy to understand the coupling between the stator circuit and the rotor circuit.
Moreover, in the new state-equation after the decoupling control, the transfer function becomes the first-order without the rotor resistance. Therefore, it becomes easy to design the control system for decoupling.
In addition, experimental results using the designed current controller are given.
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