Detection and Calculation Method of AC Motor Current RMS

Abstract

The invention discloses a detection and calculation method for AC motor current's effective value with the carrier wave frequency of the motor being set as fc. The method comprises the following steps: starting the motor; accessing and recording its initial electrode polarity; accessing the real-time electrode polarity of the motor once every time period of T; when the real time electrode polarity is opposite to the initial electrode polarity, recording the motor frequency value f at the opposite electrode polarity sampling point and the motor current value I1; and at the same time, accessing and recording the motor current values I2, I2, I3,....In once every time period of T; when the real-time electrode polarity of In is consistent with the initial electrode polarity and the real-time electrode polarity of In is opposite to that of In+1, stopping the recording of the motor current value and abandoning the motor current value In +1; determining whether the sampled number n is in the range calculated by the figure; if not, returning to step 2; and otherwise, successfully determining the effective current value as described in the figure. The method can accurately detect and calculate the motor current's effective values in non-standard sine wave waveforms.

Description

technical field [0001] The invention relates to the technical field of real-time detection of sine wave effective value, in particular to a detection and calculation method for detecting the effective value of AC motor current. Background technique [0002] The AC motor (hereinafter referred to as the motor) is designed and operated according to the characteristics of the standard sine wave current, so the detection and calculation of the effective value (Irms) of the motor current is also based on the standard sine wave AC, by detecting the peak or average value to convert Get the effective value of the current. [0003] The detection and calculation method of the effective value of the motor current in the prior art is as follows: the first method connects a current detector on any phase of the motor, and obtains an extreme value by continuously comparing the output of the current detector within a certain period of time. That is, the current peak value Ipeak of the motor...

AI Technical Summary

Problems solved by technology

The second method is to sample N times in a sinusoidal signal cycle to obtain a sample value of I 1 , I 2 , I 3 ... I N , then the average current Current RMS The above two methods are only applicable to the current RMS calculation when the current waveform is a standard sinusoidal waveform

However, due to the influence of the characteristics of the frequency converter, a large number of high-order harmonics will be generated in the current of the motor, especially for a motor with torque control, the generated current waveform will seriously deviate from the standard sinusoidal waveform

Therefore, the above two kinds of motor current RMS obtained by detecting the peak value or average value respectively have the following technical disadvantages: since the detected current waveform is not a standard sine wave, the calculated current RMS value has a large deviation and low accuracy.

For torque-controlled motors or motors that deviate from the sine wave current, the calculation result of the effective value of the current is inaccurate, which will not only affect the reliability of the motor product, but also cause damage to the motor

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