Application of Interpolating Polynomials for the Active Power Within a Given Frequency Band Measurement

At present, the active power within a given frequency band is considered as one of the most important and informative parameters of electric power distribution systems. Digital systems of active power measurement are widely spread. Such systems implement methods of polynomial interpolation of a sampled instant power signal. Simulation modeling shows that the polynomial interpolation can be successfully applied to measure active power of both sinusoidal and polyharmonic input signals. The paper considers application of zero, first and second order polynomial interpolation (the algorithms of active power measurement are considered). Analytic expressions that allow to evaluate active power measurement systematic error are derived. The influence of input signal parameters like amplitudes of voltage and current, frequency and frequency deviation, phase shift between voltage and current and measurement system parameters such as sampling frequency, total measurement time on active power measurement systematic error for interpolation polynomials of zero, first and second order are described. The measurement systems based on the polynomial interpolation of sampled signals are simulated in Matlab Simulink software. Zero systematic error conditions are formulated for the interpolation polynomials of the zero, first and second order. The method of the systematic error minimization by means of input signal frequency measurement and measurement time adjustment is developed.