電流形インバータ駆動誘導電動機ベクトル制御系の線形モデル

概要

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The vector control of an induction motor has made an epoch-making progress in the torque control. If the system is ideal, the torque transfer function should be constant under the vector control. Actually, however, the change of rotor resistance, the control capability of stator currents and the sampling of digital controller cause the transient state. In order to study these unfavorable effects, this paper proposes a linear model for the current source inverter-fed induction motor drive system.Firstly, a linear continuous system model is derived by using a small displacement method, and the ideal characteristics of the vector control are theoretically clarified in the proposed analytical model.Secondly, the system in which the vector control is carried out by a microprocessor is analyzed. A linear sampled-data system model is derived considering the effects of the sampling period and the dead time.The last part of this paper discusses the computed results concerning the trajectories of poles and zeros, and the transient responses to the interesting system parameters such as PI current control gain Ki, rotor resistance and sampling period. What is acquired in the analysis gives vital directions for the design of the system, for example, the selection of the gain Ki, should be a large one to stabilize the system, but it should not exceed an upper bound value caused by the sampling.