AC motor rotating speed measuring method, AC motor rotating speed control method, and AC motor rotating speed control system

Abstract

The invention discloses an AC motor rotating speed measuring method. The method comprises: first of all, observing the torque current and observation rotating speed of an AC motor by using a rotating speed observation model; then obtaining the measurement rotating speed of the AC motor by using a speed sensor, performing proportional-integral regulation through a PI regulator by taking the measurement rotating speed and the rotating speed of the AC motor previously obtained as input, and obtaining an output quantity K, wherein the initial value of the output quantity K is a preset fixed value; and by taking the multiplication product of the output quantity K and the torque current as a rotating speed deviation, subtracting the rotating speed deviation from the observation rotating speed so as to obtain the final rotating speed of the AC motor. The invention also discloses an AC motor rotating speed control method and an AC motor rotating speed control system. By taking the rotating speed of the AC motor obtained by the above rotating speed measuring method as a feedback rotating speed, closed loop control is performed on the rotating speed of the AC motor. Compared to the prior art, by adopting the provided methods and system, the output rotating speed of a motor can be more accurately controlled, and the robustness of a motor rotating speed control system is improved at the same time.

Description

technical field [0001] The invention relates to a control method of an AC motor, in particular to a speed control method and a control system, and belongs to the technical field of motor control. Background technique [0002] In the speed feedback control of AC motors, the existing methods are generally divided into two types: the first is to obtain the feedback speed through the actual measurement of the speed sensor, and then modulate the torque command through the closed-loop controller according to the speed command and speed feedback. The command is then passed through the inverter controller to modulate the output voltage and current to the AC motor. The second method does not require a speed sensor. The three-phase or two-phase stator input current of the AC motor is obtained by sampling the current sensor, and the feedback speed of the motor is obtained by observing the speed observation model (such as the most common current model or voltage model), and then accordi...

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Problems solved by technology

[0003] In the first method, since the sampling frequency of the rotational speed feedback signal calculated by the encoder is relatively slow, the sampling time is generally around 100ms. However, in the rotational speed control device, the sampling frequency of the rotational speed command is fast, and the sampling time is generally one carrier cycle, generally between 100ms About 500us, so the feedback speed in the speed control lags behind the actual motor speed, there is a time delay problem of the feedback speed, which makes the output torque command inaccurate, and the torque command is output voltage and current modulated by the inverter controller Inaccurate, which affects the accuracy of speed control, and this method relies too much on the speed sensor, so once the speed sensor is damaged or the accuracy is not high, the control of the inverter will go wrong, resulting in the instability of the entire system

The second method is greatly affected by the parameters of the motor, and due to the different changes in the working conditions of the motor and the influence of the environment, the stator resistance and rotor resistance of the motor will change with the operation of the motor. In the high-speed square wave mode, due to the output current , the voltage waveform is poor, the current decoupling is very difficult and the accuracy is not high, which affects the calculation accuracy of the motor rotor speed, and the inaccurate calculation of the speed will directly lead to the accuracy of the output torque, so the speed of the motor cannot be accurately controlled, and the motor cannot be fully utilized. power of

[0004] In summary, the existing speed control methods for AC motors, whether using the first or the second method, have low control accuracy and reliability.

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