Inverter vector control principle and characteristics

Vector control is through the size of the circuit to control the motor stator current vector coordinates and phase, in order to achieve the motor in the d, q, 0 axes of excitation current and torque current are controlled respectively, and then achieve the goal of control motor torque. By controlling the role of each vector sequence and time as well as the effect of zero vector, and can form a variety of PWM wave, to achieve a variety of control. Such as formation of switch is the minimum number of PWM wave to reduce switching loss. At present in the actual application of vector inverter control methods are mainly based on slip frequency control of vector control mode and speed sensorless vector control method of two kinds. Based on slip frequency vector control method with the slip frequency control means the steady characteristics are the same, but based on slip frequency vector control, by coordinate transformation to control the phase of the motor stator current, make it meet the certain conditions, in order to eliminate the torque current fluctuations in the process of transition. Therefore, based on slip frequency vector control method than the slip frequency control method can get a lot of improvement in terms of output characteristic. But, this kind of control mode belongs to the closed loop control mode, need to install speed sensor in the motor, therefore, the application scope is limited. Speed sensorless vector control is through the coordinate transformation processing, respectively, to control excitation current and torque current, and then by controlling the motor stator winding voltage and current on the recognition speed control in order to achieve the purpose of the excitation current and torque current. This kind of control mode, wide speed range and big start torque, reliable work, convenient operation, but the calculation is more complex, generally requires a dedicated processor for calculation, therefore, is not too ideal, real-time control accuracy is affected by the calculation accuracy.