u(x-π2)i(x)dx.u(x-π2)is the voltage signal with a -90° phase shift
which the Hilbert transform can meet with. In favor of the computing on computer
the discrete Hilbert transform has been used. The measuring error
which is caused by the sampling error or electrical-net frequency drift error
can be overcomed
to a certain extent
by the measurment techniques with quasi-synchronization. The measuring accuracy of reactive power can be highly acquired with quasi-synchronization discrete Hilbert transform.