1C31132G01 变频器的VC控制方式的做法是将异步电动机在三相坐标系下的定子电流

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1C31132G01 变频器的VC控制方式的做法是将异步电动机在三相坐标系下的定子电流

变频器的VC控制方式的做法是将异步电动机在三相坐标系下的定子电流Ia、Ib、Ic、通过三相－二相变换，等效成两相静止坐标系下的交流电流Ia1Ib1，再通过按转子磁场定向旋转变换，等效成同步旋转坐标系下的直流电流Im1、It1(Im1相当于直流电动机的励磁电流；It1相当于与转矩成正比的电枢电流)，然后模仿直流电动机的控制方法，求得直流电动机的控制量，经过相应的坐标反变换，实现对异步电动机的控制。其实质是将交流电动机等效为直流电动机，分别对速度，磁场两个分量进行独立控制。通过控制转子磁链，然后分解定子电流而获得转矩和磁场两个分量，经坐标变换，实现正交或解耦控制。矢量控制方法的提出具有划时代的意义。然而在实际应用中，由于转子磁链难以准确观测，系统特性受电动机参数的影响较大，且在等效直流电动机控制过程中所用矢量旋转变换较复杂，使得实际的控制效果难以达到理想分析的结果。

变频器的SVPWM控制方式是以三相波形整体生成效果为前提，以逼近电机气隙的理想圆形旋转磁场轨迹为目的，一次生成三相调制波形，以内切多边形逼近圆的方式进行控制的。经实践使用后又有所改进，即引入频率补偿，能消除速度控制的误差；通过反馈估算磁链幅值，消除低速时定子电阻的影响；将输出电压、电流闭环，以提高动态的精度和稳定度。但控制电路环节较多，且没有引入转矩的调节，所以系统性能没有得到根本改善。

1C31132G01 变频器的VC控制方式的做法是将异步电动机在三相坐标系下的定子电流

The VC control method of the inverter is to convert the stator current Ia, Ib, Ic of the asynchronous motor in the three-phase coordinate system into the AC current Ia1Ib1 in the two-phase stationary coordinate system through the three-phase two-phase transformation, and then transform by directional rotation according to the rotor magnetic field. It is equivalent to the DC current Im1 and It1 in the synchronous rotating coordinate system (Im1 is equivalent to the excitation current of the DC motor; It1 is equivalent to the armature current proportional to the torque), and then imitate the control method of the DC motor, obtain the control quantity of the DC motor, and achieve the control of the asynchronous motor through the corresponding coordinate inverse transformation. In essence, the AC motor is equivalent to the DC motor, and the two components of the speed and magnetic field are independently controlled. By controlling the rotor flux linkage, and then decomposing the stator current, the torque and magnetic field components are obtained, and orthogonal or decoupled control is realized by coordinate transformation. The proposed vector control method has epoch-making significance. However, in practical application, because the rotor flux is difficult to be accurately observed, the system characteristics are greatly affected by the motor parameters, and the vector rotation transformation used in the control process of the equivalent DC motor is complicated, the actual control effect is difficult to reach the ideal analysis result.

The SVPWM control mode of inverter is based on the premise of the whole generation effect of three-phase waveform, and the purpose of approximating the ideal circular rotating magnetic field trajectory of the motor air gap is to generate three-phase modulated waveform at one time, and the control is to approximate the circle by the inner tangent polygon. After practical use, it has been improved by introducing frequency compensation, which can eliminate the error of speed control. The flux amplitude is estimated by feedback to eliminate the influence of stator resistance at low speed. The output voltage and current are closed to improve the dynamic accuracy and stability. However, there are many control circuit links, and no torque adjustment is introduced, so the system performance has not been fundamentally improved.