Multi-Loop Design of Virtual Synchronous Machine Control for DFIG-Based Wind Farms

TL;DR

The paper tackles the challenge of providing inertia, damping, and voltage support in wind farms with converter-based generation by introducing a coordinated frequency-domain loop-shaping approach for VSM-controlled DFIGs. It retains loop-to-loop and machine-to-machine couplings, converts to 1-DOF controllers for tractable loop shaping, and uses a full small-signal linearisation to compute local plants and actual open-loop margins. An interaction-based framework with impulse-response analysis defines influence and sensitivity indices, which guide a prioritized redesign that restores stability margins within a single iteration for a four-machine, 8.4 MW benchmark. Time-domain simulations show FRD controllers matching ideal second-order templates and improving post-disturbance recovery, confirming the method’s practical viability using standard tools. The work offers an industry-friendly, scalable path to robust VSM control in weak-grid conditions and sets the stage for further robust analyses and experimental validation.

Abstract

The displacement of synchronous generators by converter-interfaced renewable energy sources obliges wind farms to provide inertia, damping, and voltage support, above all in increasingly weak grid conditions. This paper presents a co-ordinated frequency-domain methodology for tuning all control layers of doubly-fed induction generators (DFIGs) within a wind farm operated as a Virtual Synchronous Machine (VSM). Starting from a full small-signal linearisation that preserves loop-to-loop and machine-to-machine couplings, the procedure reshapes every local open loop to explicit phase-margin targets through a single, prioritised iteration. The resulting controllers provide a step response and stability margins close to those programmed at the design stage, in spite of the cross coupling between control loops. Since controller synthesis relies exclusively on classical loop-shaping tools available in commercial simulation suites, it is readily applicable to industrial-scale projects.

Figures (10)

• Figure 1: Single-line diagram of the VSM-controlled DFIG wind-farm system.
• Figure 2: Simplified grid-frequency dynamics with aggregate damping $D_{\!eq,g}$ and inertia $H_g$.
• Figure 3: Hierarchical control structure of a VSM-controlled DFIG generating unit.
• Figure 4: Current-control loops of the DFIG.
• Figure 5: Multiple-controller diagram for interaction analysis.