[Abstract] This paper studies a frequency conversion electromotor system composed of a voltage vector transducer and an induction motor. By establishing the mathematical model of this closed-loop control system, its transfer function is derived. It has a transfer function extremely similar to that of a thyristor-controlled DC speed regulation system, thus the system can be controlled using the closed-loop control of a DC electromotor. Satisfactory results are obtained through actual testing. [Keywords] Induction motor ; Transducer; Transfer function; Closed-loop control 1. Introduction The mathematical model of an induction motor is a high-order nonlinear, strongly coupled, multivariable system. In order to improve the static and dynamic performance of the induction motor, the frequency converter and the induction motor are combined into an induction motor system and closed-loop control is adopted to achieve this purpose [1]. The frequency converter used is an inductor vector control PWM frequency converter. It starts from the perspective of direct control of motor torque, uses three-phase symmetrical voltage power supply, establishes the ideal magnetic flux of the motor stator as the reference, and supplies power to the induction motor by different switching modes of the three-phase inverter. The actual magnetic flux tracks the reference magnetic flux to determine the switching mode of the frequency converter, thereby forming a PWM wave [2]. In this way, the strong coupling of the induction motor can be approximately decoupled. The influence of rotating voltage is ignored, and it is assumed that nonlinear relationships can be linearized. The mathematical model of the frequency converter induction motor system obtained in this way is very similar to that of the DC motor. Therefore, the relatively mature engineering design method of DC speed regulation system can be used to control the system to improve the static and dynamic performance of the system. For details, please click: Design of Closed-Loop Control System for Induction Motor