According to the standard sine and cosine functions provided by the CPU

it is necessary to calculate the active and reactive components of the fundamental voltage and current by measuring the reactor terminal voltage and current. According to the phase relationship between the fundamental voltage and current

reactor loss formula can be deduced. Due to the loss calculation value for each cycle fluctuations

it is necessary to limit the calculating result waved of the reactor loss by using the digital Butterworth filter. Test results show that the error of the phase angle is less than 0. 72 degree

the error of the fundamental loss is less than 0. 2%

indicating that the method is feasible and the measurement results are accurate and reliable.