Improving the Power Reference Tracking of Virtual Synchronous Machines by Feed-Forward Control

Abstract

This paper presents a feed-forward control method for improving the power reference tracking performance of Virtual Synchronous Machines (VSMs) without compromising their main features in terms of grid forming capability and inertia emulation. The proposed approach acts directly on the phase angle used for reference frame transformations in the control system and can be generally applied to all VSM-based control schemes relying on a virtual swing equation. A small-signal model of a selected VSM implementation with the proposed feedforward control is derived. This model is utilized to assess the impact of the power reference feedforward on the operational characteristics of the VSM. The improvement of the power reference tracking capability is demonstrated by analysing the transfer function from the power reference to the power injected to the grid, as extracted from the small-signal model. The frequency domain analysis also demonstrates how the oscillation modes of the VSM and the inertial response to grid frequency perturbations remain unaffected by the proposed feed-forward control. Finally, the findings from the frequency domain analysis are verified by time domain simulations.