Stabilisation of Frequency and Voltage in an Off-Grid Power System with Energy Storage under Abruptly Variable Load

To stabilize frequency and voltage in off-grid power systems, it is most appropriate to apply the control capabilities of electrical energy storage systems (EESS), which are either already in operation for other purposes or installed specifically to smooth abruptly variable load and provide frequency control. In all cases, when formulating requirements for EESS, it is necessary to take into account the characteristics of the abruptly variable load inherent to the considered power system. For this purpose, the research proposes a sensitivity analysis of generator sets to the frequency spectrum of the load profile. Based on a mathematical model of an off-grid power system implemented in the MATLAB Simulink, the amplitude-frequency characteristics of a gas turbine generator set and a diesel generator set were calculated under different load profiles. The load power oscillation frequency values leading to electromechanical resonance hazardous to electrical machines were identified.

Algorithms for frequency and voltage stabilization are proposed combining the principles of control by disturbance and deviation. An algorithm is provided for choosing the control priority between active and reactive power when control resource of EESS is limited. It is based on the proximity of the load power oscillation frequency to the resonant frequency of the generator set and the magnitude of the deviation of the regulated parameter from its setpoint.

The effectiveness of these algorithms is confirmed by calculations based on a mathematical model of an off-grid power system with an abruptly variable load schedule of a real industrial facility. The use of EESS with the proposed algorithms makes it possible to eliminate shock frequency changes and sudden voltage drops, as well as reduce their deviations in an off-grid power system to the level typical for unified power systems.