Frequency control is an integral part of the power system management. In the Unified Energy System of Russia, the operator provides the continuous control of the electric power mode by the frequency and active power flow in order to adjust the frequency within the acceptable limits and adjust the active-power flow in the controlled sections.
Overall, frequency in the power system depends on the balance of generated and consumed power. When imbalance of power, the frequency of power system is proportionally changing. If the frequency in the power system decreases, it is necessary to increase the volume of generated active power at the power plants to achieve a normal frequency value. According to GOST 32144–2013, the frequency must be within 50,0 ± 0,2 Hz for at least 95% of the time of day, without exceeding the admissible limit values of 50,0 ± 0,4 Hz.
Frequency control in the power system is provided by three stages, which are included between themselves:
• preliminary frequency control, which provided by the connection of all power plants in the power system, i. e. control the frequency deviations within admissible limits in the event of any imbalance of activity in the power system. This type of control varies in the operation speed; it firstly adjusts any frequency of oscillations;
• secondary control, providing the recovery of the normal frequency level and power flows in the power system due to the allocated active-power reserves at the power plants;
• tertiary control, which (within the framework of frequency control) is understood as the redistribution of the reserve of the first or secondary control used in the frequency control.
In most developed countries of the world, renewable power sources are increasingly used for electricity generation, the part of which in a number of countries has exceeded for 20%. Thereat, it is relevant to study the quality parameters and characteristics of the electrical modes of operation of the SPP, during the parallel operation with the traditional power system. Joint operation of the SPP with the power system is possible only if the quality characteristics of the generated power meet the needs of the existing electric grid enterprise [1].