Influence of Reactive Power Control Loop Parameters on Small Disturbances Stability of Virtual Synchronous Control Technique

The grid-following converters are constantly weakening the inertia and frequency support ability of the power grid, as the portion of installed capacity of new energy continues increasing. To cope with the future trend of new energy grid-connected with larger capacity, the grid-forming type control technology has become a research hotspot. Among them, virtual synchronous generation control, as one of the technical routes, not only improves the proactive support capability of new energy but also brings small disturbance instability to the grid. Based on the state-space method, this article establishes a single-machine small-signal analytical model, deduces the state-space equations of the multi-machine parallel system, calculates the eigenroot and the participation factor, and analytically points out the raising of the integration coefficients in reactive power loop and the sag coefficients of reactive voltage, avails the improvement of the low-frequency damping ratio generally, as well as the enhancement of the synchronization stability under small disturbance. Finally, the correctness of the theoretical analysis is verified based on simulation examples.

I. Introduction

The increase in the proportion of new energy generation connected to the power grid has gradually shown a “double high” trend in power systems. At present, the new energy converters in stock and those to be connected to the grid in large quantities all adopt grid-following (GFL) control technology, which realizes grid synchronization through phase-locked loops (PLL) and does not have inertia and frequency proactive support capability, which has already posed a big challenge to the power grid operation. In this regard, some researchers have presented a new strategy called grid-forming control (GFM) [1], which no longer relies on the PLL and is capable of actively generating voltage amplitude and phases to achieve grid-connected synchronization.