Abstract : This paper provides a concise theoretical analysis of the principle and control strategy of sensorless vector control technology for frequency converters. It also introduces a model for calculating motor speed using model reference adaptive control theory, elucidates the influence of various factors on speed estimation and effective correction measures, and provides engineering application test records. Keywords : Frequency converter; Vector control/Speedless; Model reference adaptive 1 Introduction This paper analyzes sensorless vector control technology to digest and absorb advanced speed control technology. To date, sensorless vector control remains a complex and important research topic in frequency converter speed control technology. 2 Vector Control Principle To simulate the control of asynchronous motor torque in a manner similar to that of a DC motor, the primary current is decoupled into torque (q-axis) and flux (d-axis) components, and these two components are used to synthesize a three-phase AC current for control. However, the rotor speed ωr needs to be detected. ω is expressed as follows: ω is controlled according to equation (1), and Te is controlled by the magnitude of the magnetic flux and the q-axis current i[sub]qe[/sub] in equation (2). Therefore, the basic control idea is to make the d-axis magnetic flux Φ[sub]d[/sub] equivalent to the magnetic field of the DC motor, and i[sub]qe[/sub] equivalent to the electrode current of the DC motor. That is, by measuring and controlling the stator current vector of the asynchronous motor, the excitation current and torque current of the asynchronous motor are controlled respectively according to the principle of magnetic field orientation. Thus, the purpose of controlling the torque of the asynchronous motor is achieved. 3 Speed ​​estimation method and calculation As mentioned above, in order to realize vector control, speed must be detected, that is, there must be speed feedback. The speed sensorless vector control adopted by the frequency converter in this paper is derived by using indirect calculation and model reference adaptive system theory and selecting a suitable reference model. A speed estimation unit is designed in the frequency converter in this paper to realize that the error between the secondary magnetic flux Φ[sub]2[/sub] of the induction motor (IM) and the Φ[sub]2[/sub] of the internally modeled IM is zero. By changing the parameters of the estimated speed model, the rotational speed can be determined. Specifically, the flux error is calculated based on the deviation between the primary voltage applied to the IM and the model voltage. This error, along with the estimated speed, is then used to perform vector control of the frequency converter via a PI controller. (Read full article: Analysis of Sensorless Vector Control for Frequency Converters)