After the microcontroller samples the three-phase voltage current signal, if the accuracy requirements are not very demanding, we can use the symmetric component method to calculate the positive and negative sequence and the zero sequence components. Enables monitoring of faults.
Symmetric component method formula:
Figure 1 symmetrical component formula
where a is the complex factor
Figure 2 recalculates the factor
According to the positive and negative sequence derived from the symmetrical components and the calculation formula of zero sequence, we will set the number of points sampled by AD to be a multiple of 3, such as 72, 78, 96, etc., which is set to facilitate the shift processing of the sampled signal.
Multiplying the sampled signal by the complex factor a (a square) is actually moving the vector signal 120° to the right or left.
For example, if we collect a signal of 96 points, then shifting the right 120° is actually to swap the storage position between the last 32 points of the sampling array and the previous 64 points, and the same reason left shift is to swap the storage position between the last 64 points of the array and the previous 32 points.
In this way, you can directly use the above zero-order and positive and negative sequence formulas to calculate the vector signal of the zero-order components and positive and negative sequence components, and then through the square mean root or DFT or other methods, the effective value of the signal can be obtained.
For occasions where the accuracy requirements are not high, this is a good choice, but if the accuracy requirements are relatively high, then adding a certain amount of compensation for this method should also be able to meet the requirements. If there are professionals who know how to compensate for higher accuracy, please do not hesitate to teach.