The monograph has solved an actual scientific problem, improving the efficiency of electricity networks by developing methods of compensation current non-active components under harmonic distortions and unbalance of mains supply voltage. The research of the compensation system working processes in time- and frequency-domain allows to reach the positive effect for the developed method. The necessity of the analytical methods for analysis of nonlinear elements of electrical systems in the frequency-domain development have been grounded. The expediency and efficiency of the usage of small parameter method, which is realized in frequency-domain using instantaneous admittance components, have been grounded. It is shown that application of a small parameter method with its realization in frequency domain enables significant simplification of the process of the analysis of electric circuits with semiconductor converters in an analytical form and facilitation of calculation automation. Based on this, the algorithm for calculation of the passive filter parameters have been proposed. This allows to reach the desired voltage total harmonic distortion coefficient. The analysis of energy consumption and conversion in electrical systems with semiconductor converters based on the instantaneous power components analysis allowed to make important conclusions. Based on the analysis in analytical form in the frequency domain by numerical analysis and mathematical modeling of compensation, non-active components of current improvement methods were proposed as compensation non-active components under the non-sinusoidal and supply voltage unbalance and proved the effectiveness of its implementation.