Phase Angle Feed-Forward Control for Improving the Power Reference Tracking of Virtual Synchronous Machines

A method for improving the power reference tracking capability of Virtual Synchronous Machines (VSM) by phase angle feed-forward (PAFF) control is proposed in this article. The presented implementation includes compensation for the ac power flow dynamics and can be applied to any VSM-based control relying on a virtual swing equation. Fast and accurate power reference tracking is achieved independently from the emulated inertia time constant, and without influencing the grid synchronization mechanism of the VSM. Therefore, the grid forming capability of the VSM and the inertial response to grid frequency variations are not influenced by the proposed PAFF control. The effectiveness of the derived feed-forward terms is first validated with a simplified VSM scheme. The performance is also thoroughly evaluated for a detailed VSM implementation including closed loop current control and a virtual impedance. This includes operation with different grid impedance values and studies of the sensitivity of the PAFF function with respect to parameter variations in the VSM control or deviations from the assumed grid impedance. Experimental results with a 50 kVA converter controlled as a VSM are presented as verification of the improvement in power reference tracking capability.