Abstract
Grid-forming power converters (GFMC) have been widely adopted in power systems as an attractive solution against the challenges imposed by the ever-increasing penetration of renewables. Despite its versatility, GFMC is employed only to provide islanded operation, grid regulations, and synthetic inertia. To further extend the use of GFMC in enhancing power system stability, this paper proposes a multi-rotor virtual machine (MRVM) controller to attenuate sub-synchronous oscillations. Driven by the formulation of a virtual synchronous machine (VSM), the proposed MRVM implements a VSM-based GFMC with several virtual rotors whose electromechanical characteristics can be individually adjusted to target specific oscillatory modes in the system. In this work, the MRVM’s working principle is described in detail and tuning guidelines are proposed to simplify the selection of control parameters by using frequency-domain techniques and the eigenvalue locus analyses. To validate the performance of the MRVM, an IEEE benchmark grid model is adopted namely, the three-machine-infinite-bus system. It is evident from the results that the MRVM (i) provides higher degrees of freedom when dealing with sub-synchronous oscillations, and (ii) outperforms conventional GFMC, especially in damping intra-area power oscillations.
Highlights
Low-frequency oscillations (LFO) exist naturally in power systems due to the power exchange between generating units operating in parallel and when interconnected through long transmission lines [1], [2]
The damping of Grid-forming power converters (GFMC) to LFO can be maximized in a selective manner without comprising significantly the overall performance of the GFMC
Comparing to the synchronous power controller (SPC)-GFMC, the damping of interarea mode is increased from 8% to 11%
Summary
Low-frequency oscillations (LFO) exist naturally in power systems due to the power exchange between generating units operating in parallel and when interconnected through long transmission lines [1], [2]. To improve the performance of the SPC-GFMC, a tuning method is proposed in [27] This tuning approach aims to reduce the phase lag by adjusting the controller damping ratio ζ . The work in [34] demonstrated that frequency-selective damping methods might offer better performance in suppressing LFO Motivated by such a demonstration, this paper coins a new concept, namely MRVM, to fully exploit the virtualization paradigm in controlling GFMC. Whereas the other virtual rotors, rotating at ω1 and ω2, can be tuned with {H1, D1} and {H2, D2}, respectively, to provide adjustable damping to different electromechanical modes In this way, the damping of GFMC to LFO can be maximized in a selective manner without comprising significantly the overall performance of the GFMC. Decoupling the dynamics of the virtual rotors simplifies greatly the tuning of the control parameters
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