Abstract
Power-synchronization control (PSC) is a promising control strategy to improve the stability and performance of voltage-source converters (VSCs) in ultra-weak AC grids. However, evaluation of PSC to date has investigated performance only at single controller operating points, rather than holistically varying multiple controller gains. This paper develops a new methodology, based on small-signal eigenvalue analysis, to comprehensively analyze PSC-VSC stability. The maximum active power transfer of PSC is established across a broad range of controller tunings and the two-way and three-way couplings between the power-synchronization control, AC voltage control and high-pass current filter gains are quantified. A new stable tuning region is introduced, which represents the controller parameter space for stable operation. It is shown that PSC can achieve rated power transfer into an AC grid (short circuit ratio(SCR)=1) at multiple controller operating points, but dynamic performance varies significantly within this region. The robustness of this operating region to SCR changes is also investigated. The stability boundary and dynamic performance are validated using control hardware-in-the-loop experiments with a real-time digital simulator. Practical recommendations arising from this work are a set of controller gains that provide stability and good dynamic performance at high power transfer for ultra-weak grid-connected VSCs employing PSC.
Highlights
Renewable energy generation and energy storage are being integrated into power systems at an accelerating rate worldwide [1]
The preferred choice to interface these installations to an AC grid is the voltage-source converter (VSC) due to their good control performance and improved performance in weak AC grids [2], [3]
Of the power synchronization loop, AC control loop and high-pass current filter gains have been assessed, revealing that the high-pass filter has the potential to increase the stable operating space if correctly tuned and that tuning of this gain is increasingly critical as the PSL or AC voltage loop (AVL) bandwidths increase
Summary
Renewable energy generation and energy storage are being integrated into power systems at an accelerating rate worldwide [1]. This paper makes the following contributions: 1) The bidirectional active power limits of a PSC-VSC in an ultraweak AC grid (SCR=1) are established across a wide range of controller parameters and bandwidths, 2) The impact of individual PSC controller gains on overall stability is quantified, 3) The two-way and three-way coupling between the active power control, AC voltage control and high-pass current filter are evaluated, and 4) all controller operating points of the PSC which maintain converter-controller stability and meet specific transient performance requirements at a given active power demand are quantified and validated using CHiL experiments. The approach detailed in this paper can be applied to any grid-connected PSC system to provide a description of the stable controller operating space, achievable power transfer limits and the controller dynamic performance, without the need for computationally-expensive time-domain simulations. This work provides a fast, generalizable approach for analyzing PSC-controlled VSC systems under any operating parameters
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