Research On Time Domain And Frequency Domain Reactive Power Measurement Based On Fourier Transform

The control and compensation of reactive power is very important for energy saving in power systems. And the premise of reasonable control and compensation is the accurate and real-time measurement of reactive power which is a key index to evaluate the power quality. Therefore, the measurement of reactive power is of great significance.Based on the definition given by Budeanu, this dissertation discusses frequency domain and time domain reactive power measurement, both based on the Fourier transform.In the discussion of frequency domain method, we emphasize on the windowed interpolation algorithm for harmonic parameter measurement, and comprehensively analyze the various interpolation algorithms brought forward by scholars home and abroad. The introduction of frequency domain measurement lays a solid foundation for the following introduction of time domain measurement.Most effort is put on the analysis of the time domain reactive power measurement. First, we discuss the phase shift of signals based on Hilbert transform, and bring forward a fast windowed discrete Hilbert transform based on FFT and IFFT. Simulation and experiment demonstrate that, as to a signal sampled 128 points per period, the fast method can save more than 50 percent of the calculating time.At last, this dissertation employs fast windowed discrete Hilbert transform and interpolation algorithm in the reactive power measurement, and bring forward two time domain methods each with its own features. The first one of them has simple realization procedures, high measuring speed, and high precision. When the sampling is asynchronous, the relative errors are within the magnitude of 10-4 by only utilizing two-period sampling points. Its deficiency is the sharp decreasing of measuring precision under the background of strong noise and large interharmonics. On the basis of the first method, appropriate adjustment is carried out on the second one, which leads to its stronger anti-interference ability. Simulation shows that, with presence of interharmonics, white noise and synchronization error, the relative errors are still within the magnitude of 10-4. The deficiency of this method is that the duration of sampling window should always reach more than ten signal periods, so the measuring real time needs further improvement. In practice, we can make reasonable choice between the two methods according to practical requirement.The dissertation combines frequency domain reactive power measurement with time domain reactive power measurement, carries out some original work for the application of windowed interpolation algorithm in time domain reactive power measurement, and provides more algorithm choices for software design of reactive power measurement in real instruments.