Adaptive Control Algorithm Based on a Virtual Synchronous Generator. Part I

Abstract

In modern hybrid power systems, the total system inertia is not a constant value and at any given time depends on the share of renewable energy sources (RES) generation that are connected to the network via power converters. Because of this, the restrictions required in the power systems on the rate of change of frequency and the magnitude of its deviation during disturbances become difficult to achieve with conventional approaches and measures. Therefore, the transition to a new strategy of RES control, in which the power converter becomes the grid-forming, allowing the latter to perform a number of necessary system services, is relevant. To this end, a control algorithm based on the virtual synchronous generator (VSG), which imitates the properties and capabilities of conventional synchronous generation for RES units, can be used. However, due to constantly changing operating conditions in hybrid power systems, the virtual inertia formed by VSG must be adaptive. At the same time, the efficiency of adaptive algorithms largely depends on the VSG structure used. In this connection, the paper proposes a modified VSG structure for which the transfer function of the active power control loop is formed. It was used to perform a comparative analysis of traditional and modified VSG structures. The analysis results are proved that the developed structure does not have three principal contradictions. It is possible to flexibly control the modified VSG parameters to achieve the desired quality of the dynamic response at any stage of the transient process due to these special properties. The influence of tuning parameters on the inertial and damping properties of VSG is analyzed in the second part of the paper. The adaptive algorithms of the parameters changed depending on the emerging grid conditions have been developed on the basis of the obtained results. The obtained analytical results are confirmed by nonlinear dynamic simulation.