[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"doc-detail-84080-en":3,"doc-seo-84080-105":30,"detail-sidebar-cat-0-en-105":91},{"code":4,"msg":5,"data":6},0,"success",{"doc_id":7,"user_id":8,"nickname":9,"user_avatar":10,"doc_module":4,"category_id":11,"category_name":12,"doc_title":13,"doc_description":14,"doc_content":15,"file_id":16,"file_url":17,"file_type":18,"file_size":19,"view_count":20,"is_deleted":4,"is_public":21,"is_downloadable":21,"audit_status":21,"page_count":22,"language":23,"language_code":24,"site_id":25,"html_lang":24,"table_of_contents":26,"faqs":27,"seo_title":13,"seo_description":14,"update_tm":28,"read_time":29},84080,1099514067415,"Rowan","https://ap-avatar.wpscdn.com/avatar/100002539d78ffe74a7?x-image-process=image/resize,m_fixed,w_180,h_180&k=1779092875211072502",8,"Research & Report","Structural Analysis and Internal Stability Enhancement of Virtual-Admittance-Based Cascaded GFMIs Under Unity Voltage-Feedback Decoupling","Virtual admittance (VA) control is widely used for cascaded voltage-control and current-control grid-forming inverters (GFMIs), since it shapes converter terminal behavior while preserving the inner current-regulation path. Achievable voltage-control (VC) bandwidth remains strongly coupled to current-control (CC) bandwidth and VA parameters. Unitygain voltage-feedback decoupling (VFD) seems to fully decouple loops, but it removes a low-frequency restoring term tied to the filter capacitor, creating an internal-stability limitation termed the VFD trap. A proportional active-damping path restores the missing support without reducing VFD and enables delay-aware VC tuning. Experiments on a 3-kVA prototype confirm faster voltage settling and stable power injection.","Structural Analysis and Internal Stability Enhancement of Virtual-Admittance-Based Cascaded GFMIs Under Unity Voltage-Feedback  \nDecoupling  \nStephen Arinze Obi, Ki-Hyun Kim, Graduate Student Member, IEEE, and Jae-Jung Jung, Senior Member, IEEE  \narXiv :2607 .06192v1 [ ee ss . SY] 7 Jul 2026  \nAbstract—Virtual admittance (VA) is widely used in cascaded voltage-control and current-control (VC-CC) grid-forming inverters (GFMIs) because it shapes the converter terminal behavior while preserving the current-regulation path required for current shaping and limiting. However, the achievable VC-loop bandwidth remains strongly coupled to the CC-loop bandwidth and to the VA parameters. Voltage-feedback decoupling (VFD) is commonly used to relax this coupling, but in VA-based control its benefit is not unconditional. This paper shows that unitygain VFD, which represents the full-decoupling condition, removes the low-frequency restoring term associated with the filter capacitor and drives the voltage loop toward a delay-sensitive double-integrator structure. This internal-stability limitation is referred to here as the VFD trap. To address this trap without attenuating VFD, a proportional active-damping (AD) path is proposed, implemented as negative capacitor-voltage feedback in the current-reference path. The proposed path restores the missing low-frequency support while retaining unity VFD and introduces an additional AD-based degree of freedom for VCloop tuning. A minimum support condition, a delay-aware phase-margin expression, and compact forward/inverse design equations are derived for operating-point selection. Standalone and grid-connected experiments on a 3-kVA prototype verify the analysis, showing that the proposed path recovers stable unity-VFD operation, reduces the voltage-step settling time from approximately 9 ms to 3 ms, and maintains stable power injection.  \nIndex Terms—Active damping, grid-forming inverter, internal stability, virtual admittance, voltage-feedback decoupling.  \nI. INTRODUCTION  \nTHE growing share of inverter-based resources is chang  \ning power-system dynamics and increasing the need for grid-forming inverters (GFMIs) that provide voltage support, frequency support, and inertia-like behavior without relying on a stiff grid [1], [2] . These functions are typically realized by an outer synchronization or power-control layer (PCL) that establishes the converter voltage angle, together with an inner voltage-control layer that regulates the output voltage [3]–[5] . Because different inner-loop realizations lead to different dynamic limitations, this work focuses on the cascaded voltage-control and current-control (VC-CC) structure, which is widely used in practical inverter implementations [6]–[8] . In this structure, the inner voltage-control dynamics are a  \nThe authors are with the School of Electronics and Electrical Engineering, Kyungpook National University, Daegu 41566, Republic of Korea (e-mail: [mashall96@knu.ac.kr](mashall96@knu.ac.kr); [rlarlgus5615@knu.ac.kr](rlarlgus5615@knu.ac.kr); [jj.jung@knu.ac.kr](jj.jung@knu.ac.kr)).  \nCorresponding author: Jae-Jung Jung.  \nkey design constraint: insufficient bandwidth degrades voltage regulation, whereas overly aggressive tuning can introduce high-frequency stability problems [3], [9]–[11] .  \nIn cascaded VC-CC GFMIs, virtual admittance (VA) is commonly used to shape the converter terminal behavior through a prescribed admittance. The VA branch processes the voltage error between the internal voltage reference and the measured capacitor voltage and generates the current reference tracked by the inner current loop [12]–[15] . In this way, it preserves the current-regulation path required for current shaping and limiting. However, the achievable VC-loop dynamics remain strongly coupled to the CC-loop bandwidth [16] and to the selected VA parameters [12], [13],[17] . This coupling is restrictive because the VA parameters are generally selected for grid-supp","cbCaipOy2UHuhAq2","https://ap.wps.com/l/cbCaipOy2UHuhAq2","pdf",5862120,3,1,9,"English","en",105,"# Abstract\n# Introduction\n## Cascaded VC-CC GFMIs and loop coupling\n## Voltage-feedback decoupling (VFD) and its limitation\n## Motivation for the proposed active-damping path","[{\"question\":\"Why does unitygain voltage-feedback decoupling (VFD) not always improve stability in VA-based cascaded GFMIs?\",\"answer\":\"Unitygain VFD removes a low-frequency restoring term associated with the filter capacitor, pushing the voltage loop toward a delay-sensitive double-integrator structure and creating an internal-stability limitation referred to as the VFD trap.\"},{\"question\":\"What method is proposed to address the VFD trap without attenuating VFD?\",\"answer\":\"The paper proposes a proportional active-damping (AD) path implemented as negative capacitor-voltage feedback in the current-reference path. It restores the missing low-frequency support while retaining unity VFD and adds an extra degree of freedom for VC-loop tuning.\"},{\"question\":\"What experimental results validate the proposed approach?\",\"answer\":\"Standalone and grid-connected experiments on a 3-kVA prototype show stable unity-VFD operation, reduce voltage-step settling time from about 9 ms to 3 ms, and maintain stable power injection.\"}]",1784192591,23,{"code":4,"msg":31,"data":32},"ok",{"site_id":25,"language":24,"slug":33,"title":13,"keywords":34,"description":14,"schema_data":35,"social_meta":86,"head_meta":88,"extra_data":90,"updated_unix":28},"structural-analysis-and-internal-stability-enhancement-of-virtual-admittance-based-cascaded-gfmis-under-unity-voltage-feedback-decoupling","",{"@graph":36,"@context":85},[37,53,68],{"@type":38,"itemListElement":39},"BreadcrumbList",[40,44,48,50],{"item":41,"name":42,"@type":43,"position":21},"https://docshare.wps.com","Home","ListItem",{"item":45,"name":46,"@type":43,"position":47},"https://docshare.wps.com/document/","Document",2,{"item":49,"name":12,"@type":43,"position":20},"https://docshare.wps.com/document/research-report/",{"item":51,"name":13,"@type":43,"position":52},"https://docshare.wps.com/document/structural-analysis-and-internal-stability-enhancement-of-virtual-admittance-based-cascaded-gfmis-under-unity-voltage-feedback-decoupling/84080/",4,{"url":51,"name":13,"@type":54,"author":55,"headline":13,"publisher":57,"fileFormat":60,"inLanguage":24,"description":14,"dateModified":61,"datePublished":62,"encodingFormat":60,"isAccessibleForFree":63,"interactionStatistic":64},"DigitalDocument",{"name":9,"@type":56},"Person",{"url":41,"name":58,"@type":59},"DocShare","Organization","application/pdf","2026-07-26","2026-07-16",true,{"@type":65,"interactionType":66,"userInteractionCount":20},"InteractionCounter",{"@type":67},"ViewAction",{"@type":69,"mainEntity":70},"FAQPage",[71,77,81],{"name":72,"@type":73,"acceptedAnswer":74},"Why does unitygain voltage-feedback decoupling (VFD) not always improve stability in VA-based cascaded GFMIs?","Question",{"text":75,"@type":76},"Unitygain VFD removes a low-frequency restoring term associated with the filter capacitor, pushing the voltage loop toward a delay-sensitive double-integrator structure and creating an internal-stability limitation referred to as the VFD trap.","Answer",{"name":78,"@type":73,"acceptedAnswer":79},"What method is proposed to address the VFD trap without attenuating VFD?",{"text":80,"@type":76},"The paper proposes a proportional active-damping (AD) path implemented as negative capacitor-voltage feedback in the current-reference path. It restores the missing low-frequency support while retaining unity VFD and adds an extra degree of freedom for VC-loop tuning.",{"name":82,"@type":73,"acceptedAnswer":83},"What experimental results validate the proposed approach?",{"text":84,"@type":76},"Standalone and grid-connected experiments on a 3-kVA prototype show stable unity-VFD operation, reduce voltage-step settling time from about 9 ms to 3 ms, and maintain stable power injection.","https://schema.org",{"og:url":51,"og:type":87,"og:title":13,"og:site_name":58,"og:description":14},"article",{"robots":89,"canonical":51},"index,follow",{"doc_id":7,"site_id":25},{"code":4,"msg":5,"data":92},[93,97,101,105,110,115,120,123,127,130,134],{"id":21,"doc_module":4,"doc_module_name":46,"category_name":94,"show_sort_weight":95,"slug":96},"Story & Novel",90,"story-novel",{"id":47,"doc_module":4,"doc_module_name":46,"category_name":98,"show_sort_weight":99,"slug":100},"Literature",80,"literature",{"id":52,"doc_module":4,"doc_module_name":46,"category_name":102,"show_sort_weight":103,"slug":104},"Exam",70,"exam",{"id":106,"doc_module":4,"doc_module_name":46,"category_name":107,"show_sort_weight":108,"slug":109},5,"Comic",60,"comic",{"id":111,"doc_module":4,"doc_module_name":46,"category_name":112,"show_sort_weight":113,"slug":114},6,"Technology",50,"technology",{"id":116,"doc_module":4,"doc_module_name":46,"category_name":117,"show_sort_weight":118,"slug":119},7,"Healthcare",40,"healthcare",{"id":11,"doc_module":4,"doc_module_name":46,"category_name":12,"show_sort_weight":121,"slug":122},30,"research-report",{"id":22,"doc_module":4,"doc_module_name":46,"category_name":124,"show_sort_weight":125,"slug":126},"Religion & Spirituality",20,"religion-spirituality",{"id":125,"doc_module":4,"doc_module_name":46,"category_name":128,"show_sort_weight":125,"slug":129},"World Cup","world-cup",{"id":131,"doc_module":4,"doc_module_name":46,"category_name":132,"show_sort_weight":131,"slug":133},10,"Lifestyle","lifestyle",{"id":135,"doc_module":4,"doc_module_name":46,"category_name":136,"show_sort_weight":106,"slug":137},19,"General","general"]