The spectral leakage caused by non-synchronous sampling is the main error source of phase difference measurement. In particular

for the wide range of frequency offset

the conventional phase difference method may make the measurement fail. This paper proposes an improved algorithm based on the conventional phase difference method. The improved algorithm is divided into two steps. Firstly

by analyzing the signal spectrum of the windowing

the polynomial transformation of spectral expression is conducted to speed up the sidelobes decay and further reduce the spectral leakage and the interference between the lines. Secondly

the number of sampling points of the signal to be measured is obtained by estimating the frequency offset range of the fundamental frequency of the grid

and two phase difference methods with different numbers of intercept points in the sampling sequence are employed. The number of intercept points of the second phase difference method is estimated by the fundamental frequency of the first phase difference method

to reduce the spectral leakage caused by the non-synchronous sampling. The simulation is conducted in scenarios of fundamental frequency stability

wide frequency offset range and interference with noise. The simulation results show that the measurement accuracy of the improved electrical parameters is much higher than that of the conventional phase difference method

and the sampling window length satisfies the IEC standard.