Dissipativity-Based Multiport Stability Root-Cause Identification and Mitigation for Solid-State Transformers

Jul 16, 2026

Solid-state transformers (SSTs) in high-power grid-connected applications can experience low-frequency oscillations when improperly designed control loops excite strong AC–DC port coupling, especially under weak-grid conditions. The work formulates a multiport admittance matrix including the SST’s AC dq axes and main DC port, then applies multiport dissipativity analysis to assess robust stability. Decomposed self- and coupling-dissipativity indices enable root-cause diagnosis, identifying coupling-dissipativity failure in the synchronization loop as the dominant mechanism. A dynamics-free orthogonal signal reconstruction controller reshapes admittance characteristics to mitigate the coupling deficiency, and experiments on a down-scaled prototype confirm accurate prediction and stable operation.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages14

Reading Time35 min

Introduction

Limitations of eigenvalue and impedance-based stability methods

Passivity and dissipativity theory for power electronics

Extending dissipativity to multiport and all-port SST dynamics

Dissipativity-Based Multiport Stability Root-Cause Identification and Mitigation for Solid-State Transformers Xiangyu Meng, Dong Xie, Hongjian Lin, Chunxu Lin, Xinglai Ge, Zhigang Liu arXiv :2607 .09271v1 [ ee ss . SY] 10 Jul 2026 Abstract-For solid-state transformers (SSTs) in highpower grid-connected applications, improperly designed control loops can excite strong inherent AC-DC port coupling, leading to low-frequency oscillation issues, especially under weak grid conditions. To address this problem, this article establishes a multiport admittance matrix for the SST, encompassing its AC dq axes and primary DC port, to characterize its inherent dynamics. Subsequently, a multiport dissipativity analysis is conducted to evaluate the robust stability of SST. By leveraging the decomposition of passivity conditions into distinct self-and couplingdissipativity indices, the specific root causes of instability are diagnosed. This framework reveals that a severe coupling-dissipativity failure, induced by the internal dynamics of the synchronization loop, is the dominant instability mechanism rather than a localized self-dissipativity issue. Guided by this diagnosis, a stabilizing controller featuring dynamics-free orthogonal signal reconstruction is designed to reshape the admittance characteristics of the SST. This enhancement specifically targets the identified couplingdissipativity deficiencies, thereby resolving the root cause of the instability. Finally, the stability analysis and the effectiveness of the enhancement strategy are validated on a down-scaled SST prototype. Experimental results demonstrate that the criterion accurately predicts the couplinginduced oscillations and that the enhanced controller guarantees stable operation under challenging weak-grid conditions. Index Terms-Admittance modeling, multiport systems, solid-state transformers (SSTs), stability criterion, weak grid stability. I. INTRODUCTION THE solid-state transformer (SST) is a key technology for modern power systems, offering high power density and efficiency for renewable integration and microgrids [1] . However, the dynamic interaction between power converters in a SST-enabled hybrid AC-DC grid can lead to DC bus voltage instability, which manifests as low-frequency oscillation (LFO), particularly when the system damping ratio is low [2] . Without proper damping, such oscillations can lead to severe overvoltages and overcurrents, compromising the safety and reliability of the system operation. To investigate the underlying oscillation mechanisms, several stability analysis techniques are available. Conventional approaches often rely on eigenvalue analysis [3]; however, the efficacy of this method is contingent upon obtaining a precise statespace model of the entire system. Such a model is impractical for the application at hand when the internal parameters of the converter and the grid impedance are unknown. To circumvent these challenges, impedance-based methods have emerged as the prevailing framework for stability assessment [4], [5] . This approach characterizes the converter and the grid by their respective admittances and impedances at the point of connection [6], where stability is subsequently determined by applying the generalized Nyquist criterion to their ratio. However, this method faces challenges in systems with multiple paralleled converters, where the aggregation of impedance data from all interacting converters becomes a complex and computationally burdensome undertaking [7] . As a powerful alternative that does not require a precise grid model, passivity theory offers a cornerstone for stability analysis and robust control design. Originating from classical circuit theory, it defines a system as passive if its energydissipative property holds across all frequencies [8] . However, practical stability analysis in power electronics focuses on a critical frequency range where interactions are most prominent. Theref

FAQs

What primary instability problem does the document address for solid-state transformers?

It addresses low-frequency oscillation caused by inherent AC–DC port coupling when control loops are improperly designed, which becomes especially severe under weak grid conditions.

How is the SST modeled to analyze stability in the proposed framework?

A multiport admittance matrix is built to characterize inherent dynamics, including the SST’s AC dq axes and the primary DC port.

What is identified as the dominant root cause of instability?

The dominant mechanism is a severe coupling-dissipativity failure induced by internal dynamics of the synchronization loop, rather than a localized self-dissipativity issue.

Jul 16, 2026

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