The aim of my master's thesis is to highlight the effect of voltage sags on the air conditioning system work of sterile production plants at Lek Ljubljana. In the beginning, I introduced the definition and types of voltage sags and their general impact on the operation of frequency converters. The main part is divided into four sections. In the first part, I presented the results of the analysis of voltage sags at the MV buss of the industrial network Lek Ljubljana for the period 2016 - 2017. In the second part, I theoretically explained techniques and carried out an evaluation of results for each of them. As the most suitable solution, I chose to use a DVR. The third part is about the modeling of the proposed solution, i.e. the DVR in the pscad, where I theoretically presented the individual block used. For the air-conditioning unit, I chose the equivalent of the inlet climate KDS01, which is used in the company Lek Ljubljana as a part of the air conditioning system at the Viale plant. For the source of voltage sags I used a simple short-circuit generator on line. In the fourth, the last part of the main part, I performed a simulation of the DVR for an individual type of voltage sag in pscad and gave the test results and findings for each. A review of the obtained results showed that the proposed solution for compensating voltage sags on air conditioning system Lek Ljubljana using DVR is adequate.