27-12-2012, 06:23 PM
The Research on Phase-shift Method of Reactive Power
The Research on Phase-shift Method of Reactive.pdf (Size: 465.54 KB / Downloads: 33)
Abstract—
Phase-shift method is one way of reactive power
measurement, in the method, the input voltage or current
is to phase-shift at first, then the multiplier which is used
to calculate the active power will be used to calculate the
reactive power. There are two ways to carry out phase-shift,
the one is the way which is based on the sampling points,
the other one is to use Hilbert filter. First of all, the
principle of the two methods is expatiated in this paper,
and then, they are designed and simulated on MATLAB,
and the Hilbert filter method is verified on a FPGA chip of
EP2C50 while there is no one else who has carried out the
method on FPGA chip. The results show that the method
based on sampling points is limited in practical application,
but the Hilbert filter method has the advantages of Phaseshift
accuracy and high precision measurement, it is used
widely.
INTRODUCTION
When power system is operating, there are two parts in
power provided by power grid: one part is active power for
energy conversion, and the other one is reactive power for
energy exchange between Electric and magnetic fields in the
circuit. The reactive power does not work outside, but it is
important for power supply system and the normal operation of
the load, and it will cause the voltage and power loss when it is
flowing in the power network, therefore, it is necessary to
measure the reactive power in power system.
At present, there are several methods to measure reactive
power, for example, Fourier analysis measurement method,
wavelet packet measurement method, the measurement method
based on artificial neural networks, cross-phase method and
phase-shift method.
CONCLUSION
In the paper, the relationship between reactive power and
active power is discussed firstly, then two ways of phase-shift
is introduced and simulated on MATLAB. For the method
using Hilbert filter, there are two ways introduced: window
function method and ripple Chebyshev method, from the
comparison of the two ways’ simulation results, it is clear that
the ripple Chebyshev method is better, so, at last, the phaseshift
method using Hilbert filter is carried out on a FPGA chip
by importing the filter coefficients generated by the MATLAB
using the ripple Chebyshev method. According to the
simulation results, it is clear that though the designed of the
method based on sampling points is simple and performance
requirements on the hardware is not very high,but it is limited
in practical application only used in a number of occasions with
less demanding, while the Hilbert filter method, particularly
using ripple Chebyshev method is easy to control on pass-band,
stop-band and ripple characteristics, accurate, has high
precision, more strictly linear phase, attenuation characteristics
is also better, so the method using Hilbert filter is better for
reactive power measurement.