The vector control method based on the slip frequency control is also based on the U / f = constant control, by detecting the actual speed of the asynchronous motor n, and get the corresponding control frequency f, and then according to the desired torque, respectively control The stator current vector and the phase between the two components control the output frequency f of the general inverter. The biggest feature of the vector control method based on the slip frequency control is that the fluctuation of the torque current in the dynamic process can be eliminated, thereby improving the dynamic performance of the general frequency converter. Early vector control general-purpose inverters were basically based on slip frequency control vector control.
The speed sensorless vector control method is based on the theory of field oriented control. Accurate field-oriented vector control requires installation of a magnetic flux detection device in an asynchronous motor. It is difficult to install a magnetic flux detection device in an asynchronous motor, but it has been found that even if a magnetic flux detection device is not directly installed in an asynchronous motor, it is found. The amount corresponding to the magnetic flux can be obtained inside the general-purpose inverter, and thus the so-called speed sensorless vector control method is obtained. Its basic control idea is to measure the excitation current (or magnetic flux) and torque current as basic control quantities according to a certain relational expression according to the input nameplate parameters of the motor and control the voltage on the motor stator windings The frequency is such that the command value and detection value of the excitation current (or magnetic flux) and the torque current match, and the torque is output, so that vector control is realized.
A general-purpose inverter with vector control can not only match the DC motor in the speed range, but also control the torque generated by the asynchronous motor. Because the vector control method is based on accurate parameters of the controlled asynchronous motor, some general-purpose inverters need to accurately input the parameters of the asynchronous motor when using, and some general-purpose inverters need to use speed sensors and encoders, and need to use The manufacturer-specified inverter-specific motor controls, otherwise it is difficult to achieve the desired control effect. At present, the new vector control general-purpose frequency converter already has the asynchronous motor parameter automatic identification, the adaptive function, the general frequency changer which has this kind of function can automatically identify the asynchronous motor parameter before the driving asynchronous motor carries on the normal operation, and according to The identification result adjusts the relevant parameters in the control algorithm so as to perform effective vector control on an ordinary asynchronous motor. In addition to the above-mentioned sensorless vector control and torque vector control, which can improve the torque control performance of asynchronous motors, the current new technology also includes the adjustment of asynchronous motor control constants and adaptive control matching with mechanical systems. Techniques for improving the application performance of asynchronous motors. In order to prevent asynchronous motor rotation speed deviation and obtain ideal smooth rotation speed in low speed area, the application of large-scale integrated circuits and the use of dedicated digital automatic voltage adjustment (AVR) control technology control method has been practical and achieved good results.