The paper deals with the application of a newly developed anemometer without moving parts. It is digitized and has built-in electronics that convert the vibrations of two aluminum fixed frames into two digital signals: one, which shows the strength (speed absolute value)) of the wind, and the other, which shows its direction. Both of these signals are used to calculate wind power and energy. Earlier works have shown that the two-bit stochastic digital measurement method overcomes (eliminates) the problem of the offset of the analog adder. The authors of this paper apply this idea to the digital output of the sensor, where the role of the offset of the analog adder is taken over by the integral nonlinearity of the digital output of the anemometer. The first step in this direction is digitally dithering the sensor output. This principle is presented in detail, as well as a rough estimate of the accuracy gain in measuring wind energy. The obtained result shows that the accuracy in measuring wind energy is not worse than the limit accuracy in the case of a cup anemometer that generates sinusoidal voltage.
Članak predstavlja teoriju rada dvobitnog stohastičkog konvertora. Ovaj konvertor se može koristiti za precizna i tačna merenja efektivnih vrednosti (root-mean-square-srednje kvadratne vrednosti) napona, struje, električne snage ili energije, što se primenjuje u mrežnim merenjima. Ključni doprinos rada ogleda se u teorijskom izvođenju granica greške merenih signala koristeći stohastičku metodu. Standardna devijacija merenih vrednosti tokom određenog perioda merenja definiše se kao greška. Kada tražimo izraze za merenu vrednost i njenu grešku, vreme se tretira kao nezavisna uniformna slučajna promenljiva, tako da se može primeniti teorija verovatnoće i statistička teorija uzoraka. Ovi uslovi su neophodni jer je predstavljeni problem veoma nelinearan i stohastički. Zbog toga se on ne može rešiti ni linearnom teorijom diskretnih signala i sistema, niti teorijom slučajnih procesa. Predstavljeno rešenje je generalizovano, kako bi se uključilo merenje određenog integrala proizvoda konačnog broja signala.
In this paper a special case of digital stochastic measurement of the third power of definite integral of sinusoidal signal's absolute value, using 2-bit AD converters is presented. This case of digital stochastic method had emerged from the need to measure power and energy of the wind. Power and energy are proportional to the third power of wind speed. Anemometer output signal is sinusoidal. Therefore an integral of the third power of sinusoidal signal is zero. Two approaches are proposed for the third power calculation of the wind speed signal. One approach is to use absolute value of sinusoidal signal (before AD conversion) for which there is no need of multiplier hardware change. The second approach requires small multiplier hardware change, but input signal remains unchanged. For the second approach proposed minimal hardware change was made to calculate absolute value of the result after AD conversion. Simulations have confirmed theoretical analysis. Expected precision of wind energy measurement of proposed device is better than 0,00051% of full scale.
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