Research on Vector Control of General Purpose Frequency Converter
Although DC motors and AC motors have been born for quite a long time, because the DC motor speed control system has formed a relatively complete theory and structure earlier, it has relatively good static and dynamic characteristics, so before the 1970s The whole transmission system is mainly based on the DC motor speed control system. However, due to structural reasons, DC motors have many shortcomings, such as regular replacement of brushes and commutators, which are difficult to maintain; capacity, voltage, current, and speed are limited. In contrast, AC motors have many advantages, such as low cost: low accident rate and easy maintenance; capacity, voltage, current and speed are not easily affected like DC motors.
At present, the AC speed control system has been transitioned from the initial use only to fans, pumps and other places to high-performance, fast-responding high-performance indicators. With the maturity and improvement of AC motor speed control theory. The shortcomings of the AC motor's poor speed control performance have been overcome, and now the AC speed control system is gradually replacing the DC speed control system. In the early days, the inverter used constant voltage ratio (v/f) or slip frequency (SF) control according to the equivalent circuit of the asynchronous motor, but these two methods were built on the static mathematical model of the motor. Its dynamic performance is not good. After unremitting efforts. Foreign scholars have proposed the vector control method (VectorContro1) and direct torque control (DTC), and applied it to the actual, and achieved very exciting control effects. The former decouples the stator current space vector of the asynchronous motor into the rotor excitation component and the torque component with reference to the control mode of the DC motor. The disadvantage is that the speed signal is calculated according to the coordinate transformation, so on this basis, no speed is proposed. The sensor vector control method is based on the actual phase voltage and phase current of the asynchronous motor and the stator rotor winding parameters to derive the rotational speed observation value to realize the vector control of the magnetic field orientation: while the latter does not adopt the decoupling idea, with the aid of the instantaneous space vector Calculate the flux linkage and torque of the motor and directly control the torque and flux linkage based on the difference compared to the given value.
