Features of compensation of a instantaneous reactive power in linear circuits at the transient mode and switched on load
Main Article Content
Abstract
Compensation of reactive power is one of the ways of increasing the electrical grid efficiency, theoretical foundations of which were developed at the beginning of the last century by scientists Frize and Budeanu. The development of effective control algorithms for reactive power compensation continues today. As usual, algorithms of reactive power compensation have an inertia of at least one period of network voltage. Therefore they cannot be used in transient mode because of the grid current non-stationarity. The problem of reactive power compensation in power grids with variable load is analyzed. An inefficient implementation of existing methods of reactive power compensation for this case is shown. The method of analysis of the transmitting energy between the source and the load during the transition process based on the theory of instantaneous power is proposed. The grid current on active and reactive components is expanded. The instantaneous value of power factor for estimation of reactive power value is proposed. To implement an assessment of the power factor instantaneous value the grid current represented as the sum of the steady and free components. For subsequent simplification of power factor calculation, the steady and free current components representation based on sine and cosine components is proposed. The power factor sign according to the current components values is analyzed. Time dependency of the current components in transient mode unlike for steady state is shown. The proposed method is adapted to transient processes. A method of instantaneous power factor value calculation, based on grid current calculation is proposed. The disadvantage of proposed method in transient mode is shown and proposed to estimate power factor value based on grid current and its derivatives. The procedure of calculation, prediction, and identification of power factor values based on expanded equation system is proposed. Principle of active and reactive power calculation on basis instantaneous power factor, sine and cosine current components is shown. Analysis of energy processes in the transient mode in a linear circuit of the first order is performed. A possibility of power factor negative values is shown. A reactive compensator design for transient mode is proposed. The principles of reactive power compensation based on power factor instantaneous values in transient mode are given. The necessity of active power compensation during time intervals when power factor has negative values is proved. The grid current shape after reactive power compensation is analyzed. The unipolar shape of the grid current and the same polarity with grid voltage insignificant part of the transient process is underlined. Shown, that such current behavior facilitates to the accumulation of the required energy in the reactive element within the minimum possible root mean square current of the electric grid that decreases stress to the grid during the transient process.
Ref. 13, fig. 3.
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