Hfconst = int [(16.1079 * Vu * VI * 10 ^ 11) / (un * IB * EC], where the parameter meanings are as follows:
Vu: voltage sampling input value. For example, if the voltage sampling is 6 270k Ω divided voltages, then Vu = 220 / (6 * 270) = 0.136v;

 (the default ADC gain is 1. If it is not required to multiply by the gain multiple, it is substituted into the formula.)
VI is the current sampling input value; Special attention should be paid to the need to multiply the gain of the ADC channel here. 

For example, the resistance of the manganese copper shunt is 200 μ M. assuming that IB is 5a, the ADC gain is 16 by default, 

then VI is 0.016v,
Un ：220V。
EC takes the empirical value of 3200. Finally, the hfconst is calculated to be 9957, converted into hexadecimal number 0x26e5 and 

written into the hfconst register.