A Configurable Unified Grid-Code Compliance Framework for Grid-Connected Inverters Across IEEE 1547-2018, VDE-AR-N 4110, and the Korean DER Grid Code

A Congurable Unied Grid-Code Compliance Framework for Grid-Connected Inverters Across IEEE 1547-2018, VDE-AR-N 4110, and the Korean DER Grid Code

Anil K S

Electrical and Electronics Engineering, B.M.S College of Engineering Bengaluru, India

Dr. Padmavathi K

Electrical and Electronics Engineering, B.M.S College of Engineering Bengaluru, India

Vishal Anand A G

Senior Director Bloom Energy (India) Pvt., Ltd Bengaluru, India

Abstract – Distributed energy resources (DERs) such as fuel- cell systems, photovoltaic plants, and battery energy storage are being rapidly deployed. Therefore, national and regional au- thorities have developed independent grid-interconnection codes for grid-connected inverters addressing synchronization, reac- tive power support, voltage and frequency ride-through, anti- islanding, harmonic emission, and communication behavior. Dif- ferences in numerical limits, operating philosophies and test pro- cedures between the various geographies require manufacturers to maintain parallel rmware and hardware variants , specic to each standard. This increases engineering effort, certication cost and time-to-market. Comparison of eleven functional dimensions of IEEE 1547-2018 (USA), VDE-AR-N 4110 (Germany), and

the Korean DER grid code: synchronization, reactive power capability, Volt-Var, Volt-Watt, Frequency-Watt, low- and high- voltage ride-through (LVRT/HVRT), frequency ride-through, anti-islanding, harmonic distortion limits, and communication in- teroperability. Based on the identied similarities and differences, a parameterized Unied Grid-Code Compliance Framework is proposed to recongure a single inverter hardware and control platform to comply with any of the studied codes, and by extension to other national codes, with the use of a structured rule database as opposed to code-specic rmware forks. This paper describes a generalized experimental verication technique for automated compliance testing, framework architecture, control ow and algorithms. The proposed framework is shown to reduce unnecessary engineering by using a comparative, standards-based approach while maintaining full grid code compliance margins. The approach enables DER and grid tied inverter designers to achieve multi-geography compliance from a common design baseline.

Index TermsDistributed energy resources, grid interconnec- tion, IEEE 1547-2018, VDE-AR-N 4110, Korean grid code, Volt- Var, Volt-Watt, Frequency-Watt, low-voltage ride-through, anti- islanding, grid-tied inverter, compliance framework.

1. Introduction

   The trend of decarbonized generation of electricity has led to a rapid increase of distributed energy resources (DERs),

   Identify applicable funding agency here. If none, delete this.

   including fuel-cell power plants, solar photovoltaic systems and battery energy storage systems, interconnected at the point of common coupling (PCC) of the distribution or sub- transmission network. DERs are distributed across the grid instead of relying on conventional centralized generation and are connected to the grid using power-electronic inverters, the dynamic behavior of which directly impacts the local voltage prole, frequency stability and power quality.

   As the penetration of DER increases, transmission and distribution system operators in several countries have pub- lished interconnection codes that specify mandatory grid sup- port functions for inverter-based resources to maintain grid stability. These functions typically include synchronization limits, reactive power capability, Volt-Var and Volt-Watt droop control, Frequency-Watt control, low- and high-voltage ride- through (LVRT/HVRT), frequency ride-through, anti-islanding protection, current harmonic limits and standard communica- tion interfaces for monitoring and dispatch.

   While the main control objectives are similar in all jurisdic- tions, the particular numerical limits, operating regions, default settings and test procedures adopted by each code vary signif- icantly. For example, the reactive power capability required by IEEE 1547-2018 in the United States, the VDE-AR-N 4110 code in Germany, and the Korean DER grid code are all dened with different percentages of nameplate apparent power, different sign conventions, and different response-time requirements. This divergence forces inverter manufacturers targeting multiple export markets to either support multiple parallel rmware variants, or over-design a single variant to meet the superset of all requirements, both increasing development and certication cost.

   In this paper, we (i) conduct a structured comparative analysis of three representative grid codes from North Amer- ica, Europe and East Asia, and (ii) propose a generalized, congurable Unied Grid-Code Compliance Framework that

   allows a common inverter hardware and control platform to be recongured for compliance with any of the studied codes via parameterization rather than redesign. The rest of the paper is organized as follows. Section II reviews the related literature on grid-code compliance and multi-standard inverter design. Section III highlights the research gap. Section IV shows a summary of the contributions of this work. Section V shows the comparative analysis of the three grid codes. Section VI elaborates the proposed framework. In Section VII, we present a generalized implementation and verication methodology. Section VIII presents expected results and Section IX con- cludes the paper and discusses future directions.

2. Literature Review

   The last ve years have seen a lot of attention in the power electronics literature on the grid-code compliance of inverter- based DERs, mainly due to the 2018 revision of IEEE 1547 and the concurrent development of interconnection codes in Europe and Asia.

   Much of the work has been dedicated to the IEEE 1547- 2018 standard itself, discussing its increased reactive power, Volt-Var, Volt-Watt and ride-through requirements with re- spect to the 2003 edition, and proposing controller archi- tectures able to achieve the standards default and area- EPS-operator-adjustable settings. Automated test benches with programmable AC sources and power analyzers to test enter- service, must-trip and ride-through behavior under controlled laboratory conditions are discussed in related conformance- testing literature consistent with IEEE 1547.1-2020.

   Meanwhile, a separate group of researchers working on the German VDE-AR-N 4110 code have analyzed the codes spe- cic handling of power-generating-plant types, its reactive- power-voltage characteristic curve Q(U), and its fault-ride- through (FRT) boundary curves for both Type 1 and Type 2 plants, observing that the code prioritizes continuous re- active current support throughout the duration of a voltage disturbance to help in transmission-level voltage recovery. Similar studies of East Asian interconnection codes have identied differences in ride-through depths, frequency-droop slope ranges, and relatively limited specication of harmonic and interoperability requirements, compared to IEEE 1547- 2018.

   Only a few studies have tried to directly compare grid- support functions across multiple countries, usually looking at only a few functions such as LVRT or Volt-Var, and usually concluding that while the functional intent of the codes are converging, the numerical settings, default curves and category structures (e.g. IEEE 1547s Category A/B and Abnormal Operating Category I/II/III versus VDE-AR-N 4110s Type 1/Type 2 plants) are not directly interchangeable. In terms of mplementation, recent work in IEEE Transactions on Power Electronics, IEEE Transactions on Industrial Electronics and IEEE Transactions on Smart Grid has examined congurable or software-dened inverter control architectures that decouple a xed power-stage and control-loop design from a recon- gurable layer of grid-support algorithms, often driven by

   multi-market product strategies, virtual power plant (VPP) aggregation and smart-inverter interoperability initiatives such as IEEE 2030.5 and SunSpec Modbus. These studies show the feasibility of parameter-driven function libraries for individual grid-support functions, but, in general, they have not addressed simultaneous, code-level compliance of multiple national stan- dards within a single unied architecture.

   In brief, on the one hand, the literature provides (a) de- tailed, standard-specic characterizations of the grid-support functions for IEEE 1547-2018, VDE-AR-N 4110, and the Korean grid code individually, and (b) general feasibility of congurable inverter control architectures, but without an integrated, cross-standard comparative framework, coupled to a concrete unied compliance architecture, which motivates the present work.

3. Research Gap

   Three gaps are identied from the literature review. First, the comparison of existing comparative studies generally fo- cuses on individual grid-support functions in isolation (e.g., only LVRT or only Volt-Var) instead of a comprehensive, function-by-function comparison covering synchronization, reactive power, Volt-Var, Volt-Watt, Frequency-Watt, ride- through, anti-islanding, harmonics and interoperability for the same set of countries.

   Second, although concepts for congurable or software- dened inverter control are available, the literature does not provide an architecture that directly maps a parameterized rule database to the specic divergences between IEEE 1547- 2018, VDE-AR-N 4110, and the Korean DER grid code, nor does it generalize the categorization schemes of each code (e.g., Category A/B, Type 1/Type 2) into a common internal representation.

   Third, published experimental methodologies for grid-code conformance testing are typically designed for a single target standard; a generalized, standard-agnostic test methodology that is able to stress the same unit-under-test against multiple parameter sets with minimal reconguration has not been thoroughly documented in the open literature.

   In this paper we close these three gaps with three con- tributions: a structured multi-function comparative analysis (Section V), a unied compliance architecture with an explicit parameterized rule database (Section VI), and a generalized verication methodology (Section VII).

4. Contributions

   The main contributions of this paper can be summarized as follows:

   • Comparative analysis of the IEEE 1547-2018, VDE- AR-N 4110, and the Korean DER grid code on the top- ics of synchronization, reactive power capability, Volt-Var, Volt-Watt, Frequency-Watt, LVRT, HVRT, frequency ride- through, anti-islanding, harmonic limits, and communica- tion/interoperability requirements in a structured, eleven- dimension format.

   • A generalized congurable Unied Grid-Code Compli- ance Framework that decouples a common inverter hardware and control platform from a parameterized, standard-specic rule database enabling multi-geography compliance without rmware forking.

   • A normalized internal representation that translates the different categorization schemes used by each code (e.g. IEEE 1547 Category A/B, Abnormal Operating Category I/II/III; VDE-AR-N 4110 Type 1/Type 2 plants) to a common set of congurable operating regions.

   • A generalized control owchart and ride-through decision logic that can be parameterized to any of the three studied codes and representative Volt-Var and Frequency-Watt algo- rithm descriptions.

   • A generic, automatable method for experimental ver- ication of standards, allowing compliance testing with a programmable AC source, precision power analyzer and auto- mated test sequencer.

   • A comparative discussion of the expected engineering ben- ets of the proposed framework vs. continuing with separate, single-standard inverter designs based on standards.

5. Comparative analysis of International Grid

   Codes

   This section provides a systematic comparison of the three grid codes analyzed along the eleven functional dimensions identied in Section IV. Fig. 1 illustrates the generic architec- ture of a grid-connected DER system to which these require- ments apply, and Fig. 2 summarizes the relative magnitude of selected requirements across the three codes.

   Fig. 2. Comparative prole of key grid-code requirements magnitudes across USA, Germany, and Korea.

   a relatively larger emphasis on the conditions for reconnection following a network disturbance, which includes minimum dead-time periods before automatic reclosure is allowed.

   1. Reactive Power Capability

      All three codes require reactive power capability but with different magnitudes and sign conventions. IEEE 1547-2018 requires injection and absorption capability referenced to nameplate apparent power, with two DER categories (Category A and Category B) providing progressively broader capability and operating-voltage ranges. VDE-AR-N 4110 has a compar- atively lower percentage requirement, but the DER is consid- ered as an electrical load for sign-convention purposes, which has direct implications for controller polarity and protection coordination. The Korean code is more consistent with the IEEE convention of referring to the source, but it species a single operating category, rather than the two-tier structure in the United States.

      TABLE I

      Grid Code Comparison for Enter-Service Parameters

      Parameter USA (IEEE 1547-2018)

      Germany (VDE-AR- N 4110)

      Korea (DER

      Grid Code)

      Fig. 1. Generalized grid-connected DER architecture showing the inverter power stage, sensing, compliance controller, and communication interfaces.

      A. Synchronization

      Enter-service voltage range

      Enter-service frequency range

      0.88 1.06

      p.u.

      59.0 61.0

      Hz

      0.90 1.10

      p.u.

      49.0 51.0

      Hz

      Not separately specied Not separately specied

      Synchronization requirements specify the allowable fre-

      Enter-service delay

      0 600 s 0 30 min

      (default 10

      Not separately

      quency, voltage and phase-angle deviation at the time of grid connection. IEEE 1547-2018 states tighter synchronization limits as aggregate DER rating increases to account for the proportionally larger disturbance a larger unit would impose on the point of interconnection. The Korean code and VDE-AR- N 4110 also specify closed synchronization windows, but with

      Synchronization basis

      Tiered by aggregate DER rating (f, V, )

      min) Plant-

      type-based reconnec- tion rules

      specied Code- dened recon- nection conditions

      TABLE II

      Reactive Power Capability Comparison

      Parameter	USA	Germany	Korea
      Capability (% nameplate apparent power)	44%	33%	33%
      Sign convention	DER as source	DER as load	DER as source
      Operating categories	Category A / Category B	Single cate- gory	Single cate- gory
      Constant- PF response time	10 s	240 s	10 s

   2. Volt-Var

      Volt-Var control regulates the reactive power output as a function of the measured terminal voltage to support local voltage regulation. All three codes specify a four-point (or equivalent) piecewise-linear droop characteristic, but vary in the location of the breakpoints of the curve, the maximum reactive power excursion, and the allowable ranges of response time. IEEE 1547-2018 permits a relatively broad range of response times that can be modied by the user, whereas VDE- AR-N 4110 species a longer nominal response time that is xed and intended to avoid interaction with voltage control loops at the transmission level. Fig. 5 shows a generalized Volt-Var characteristic of the kind used by the proposed framework. Breakpoints and capability limits are derived from a congurable set of parameters rather than hard-coded values.

   3. Volt-Watt

      Volt-Watt control limits active power output at high terminal voltage, reducing overvoltage contribution. This function is explicitly mandated in IEEE 1547-2018 with a settable voltage threshold and response time . It is not separately specied as a mandatory function in the VDE-AR-N 4110 or Korean codes reviewed in this work, which rely on their respective overvoltage ride-through and tripping provisions to cope with sustained overvoltage conditions.

      TABLE III

      Volt-Var and Volt-Watt Comparison

      Parameter	USA	Germany	Korea
      Volt-Var capability	44% (in- ject/absorb)	33% (in- ject/absorb)	33% (in- ject/absorb)
      Curve de- nition	User- settable points	User- settable points	Single xed curve
      Volt-Var re- sponse time	1 90 s (settable)	240 s	10 s
      Volt-Watt require- ment	Mandatory, 1.05 1.10 p.u. set point	Not separately mandated	Not separately mandated

   4. Frequency-Watt

      Frequency-Watt (frequency droop) control mimics a primary-frequency-response-like behavior by changing the ac- tive power output according to the system frequency deviation from nominal. This function is required in all three codes, but the acceptable ranges of droop slope, deadband, and response time differ. The slope for all categories is operator specied in IEEE 1547-2018 while the VDE-AR-N 4110 and the Korean code specify narrower slope ranges dened by the code. Fig. 6 displays a generalized Frequency-Watt droop characteristic with a tunable deadband and slope, consistent with the proposed framework.

      TABLE IV

      Frequency-Watt (Frequency-Droop) Comparison

      Parameter	USA	Germany	Korea
      Droop slope range	Operator- specied, all categories	2% 12%	3% 5%
      Response time	5 s	20 s (Type 2)	10 s

   5. LVRT and HVRT

      Low- and high-voltage ride-through requirements specify the voltage range and duration at which a DER must remain connected and energize the grid without interruption, and in many cases must also provide dynamic reactive current to support voltage recovery. The three codes differ considerably in the magnitude and duration of the required ride-through region. VDE-AR-N 4110 requires ride-through for a very large voltage excursion, continuous reactive current support and explicit requirements for negative-sequence current injection for unbalanced faults, reecting the focus of the code on transmission-level fault recovery. The Korean code requires ride-through down to a relatively low per-unit voltage, but does not require overvoltage ride-through. IEEE 1547-2018, however, denes multiple separate operating regions (contin- uous, mandatory, and momentary cessation) bounded by both undervoltage and overvoltage thresholds.

   6. Frequency Ride Through

   Frequency ride-through requirements also dene the oper- ating frequency ranges that must be maintained, the minimum time the system must stay online, and the maximum rate of change of frequency (ROCOF) it can handle. IEEE 1547- 2018 has the largest adjustable frequency window with a long minimum ride-through time for default settings . VDE- AR-N 4110 has a relatively more stringent ROCOF ride- through requirement . Korean standard has an intermediate ride-through range with a dened minimum holding time .

6. PROPOSED UNIFIED GRID-CODE COMPLIANCE FRAMEWORK

   The comparative analysis in Section V shows that although the eleven functional dimensions are conceptually common

   TABLE V

   Voltage and Frequency Ride-Through Comparison

   Parameter	USA	Germany	Korea
   Voltage ride- through range	0.66 1.20 p.u. (multi- region)	0.15 1.25 p.u.	0 0.90 p.u. (un- dervoltage only)
   Reactive current support during fault	Required	Required, incl. negative- sequence current	Required
   Frequency ride- through range	57.0 61.8 Hz	49.8 50.2 Hz (manda- tory band)	57.5 61.5 Hz
   Max. RO- COF with- stand	3 Hz/s	2 Hz/s	Not speci- ed

   across the standards IEEE 1547-2018, VDE-AR-N 4110, and Korean DER grid code, the numerical limits, categorization schemes, sign conventions, and default settings are differ- ent to the extent that they require conventionally standard- specic rmware. A generalized Unied Grid-Code Compli- ance Framework is proposed to address this problem, which is depicted in Fig. 3.

   Fig. 3. Proposed unied, congurable grid-code compliance framework supporting multiple international standards on common hardware.

   The framework decomposes inverter design into a common hardware platform and a recongurable compliance layer. The common hardware platform is composed of the power- conversion stage, voltage and current sensing and protection hardware, and is designed to satisfy the superset of volt- age, current and dynamic-response ratings required by any of the target grid codes. Above the hardware layer is a Country/Standard Selection Module, to select the applicable grid code at time of commissioning. The selection feeds into a Parameterized Rule Database which, for each supported standard, contains the numerical settings for each functional dimension identied in Section V synchronization windows,

   reactive power capability percentages and sign convention, Volt-Var and Volt-Watt curve breakpoints, Frequency-Watt slope and deadband, ride-through region boundaries, must-trip thresholds, harmonic limits, and the applicable communication prole.

   Each grid-support function (Volt-Var, Volt-Watt, Frequency- Watt, LVRT/HVRT, anti-islanding) is implemented in the Uni- ed Function Library as a single standard-agnostic algorithm that reads its operating parameters from the rule database (in- stead of embedding standard-specic constants). This design decision implies that adding support for another national grid code only requires the addition of a new parameter set to the rule database, not a new rmware branch. An Adaptive Ride- Through and Anti-Islanding Engine compares the real-time voltage and frequencymeasurements with the active parameter to classify the current operating point into one of several generalized regions continuous operation, mandatory ride- through, momentary cessation or must-trip as shown in the decision ow of Fig. 7. The Synchronization and Reconnection Supervisor manages the enter service and reconnection-timing rules of the active code. A Power Quality and Harmonic Compliance Block enforces the appropriate current-distortion limits. An Interoperability Layer maps internal status and command points to the communication prole associated with the active standard, for example a Modbus register map for one jurisdiction or an alternative prole for another.

   The rule database normalizes these into a common in- ternal representation which consists of an ordered set of voltage/frequency operating regions, each with a maximum duration and a required inverter response (continue, ride through with reactive support, cease energizing, or trip), as the categorization schemes used by individual codes differ (e.g. IEEE 1547s Category A/B and Abnormal Operating Cate- gory I/II/III versus VDE-AR-N 4110s Type 1/Type 2 power- generating-plant classication). This normalization makes the same ride-through engine logic reusable independent of the active national categorization scheme.

7. IMPLEMENTATION METHODOLOGY

   This section presents a generic methodology for the im- plementation and validation of the proposed framework. The methodology can be adapted to any inverter platform that can support parameterized control. The overall control ow is illustrated in Fig. 4.

   When the controller is powered up, the parameter set for the selected grid code is loaded from the rule database. The frequency and current are measured in real-time at the PCC voltage. The controller checks that measured conditions are within the enter-service window of the active code before connecting. If not, the controller holds the connection and continues measuring. Once the synchronization criteria are met, the inverter is synchronized to the grid and the active Volt- Var, Volt-Watt and Frequency-Watt functions can be activated with the loaded set of parameters. When a voltage or frequency disturbance is detected, the Adaptive Ride-Through and Anti- Islanding Engine is invoked to classify the disturbance and

   Fig. 4. Generalized control owchart of the proposed compliance from power- up to ride-through handling.

   select the appropriate response according to the decision logic of Fig. 7.

   The Volt-Var algorithm (Fig. 5) generates a reactive power setpoint as a piecewise-linear function of the measured ter- minal voltage, based on breakpoints, capability limits, and response-time constants from the active parameter set; the same algorithm structure reproduces the characteristic imposed by any of the three studied codes just by modifying the corre- sponding breakpoints. The Frequency-Watt algorithm (Fig. 6) similarly computes an active power curtailment set point as a function of measured frequency deviation from nominal, with a congurable deadband and droop slope.

   Fig. 7 shows the ride-through decision logic which classies the instantaneous voltage/frequency operating point relative to the normalized operating regions of the active code and selects one of four generalized responses: continue normal op- eration, mandatory ride-through with reactive current support, momentary cessation with monitoring for restoration or trip in accordance with the applicable must-trip table.

   Fig. 8. General methodology of compliance verication

   Fig. 5. Generalised Volt-Var characteristic (congurable per selected grid code)

   Fig. 6. Generalized Frequency-Watt droop characteristic with congurable deadband and slope

   experiment. The unit under test (UUT) is connected to a programmable four quadrant bidirectional AC source that can emulate prescribed voltage and frequency disturbance proles including ramped and stepped voltage sags/swells and frequency excursions. The responses of each code can be resolved with an adequate bandwidth and accuracy by a precision power analyzer capable of capturing the voltage, current, active power, reactive power and phase measurements at the PCC. A digital command interface (CAN, Modbus, etc.) links an automated test sequencer to both the AC source and the UUT. The sequencer executes a library of standardized test sequences voltage must-trip, frequency must-trip, voltage ride-through, frequency ride-through, Volt-Var, Volt-Watt, con- stant power factor, constant reactive power, Frequency-Watt, and Watt-Var parameterized for the currently selected grid code in the rule database. The results are logged automatically and compared with the pass/fail criteria for the active code to produce a compliance report.

   This approach generalizes the single-standard compliance test methodology into a reusable, standard-agnostic process: changing the active parameter set in the rule database is suf-

   Fig. 7. Decision ow for ride-through region classication and corresponding inverter response.

   Fig. 8. Generalized experimental methodology for grid-code compliance verication testing.

   cient to re-target the entire test sequence library at a different grid code, without changing the underlying test automation logic.

8. RESULTS AND DISCUSSION

   Considering that the present work is designed to generalize and abstract proprietary, organization-specic test data, the results presented here are a product of comparative, standards- based engineering reasoning, rather than proprietary measure- ment records. Table VII summarizes the qualitative benets expected from the proposed framework, versus retaining sep- arate, single-standard inverter designs.

   The comparative analysis in Section V suggests the pro- posed framework will provide maximum engineering benet in functions where the three codes share a common control structure but differ primarily in numerical settings Volt-

   TABLE VI

   Design Architecture and Framework Comparison

   Aspect	Single-Standard Design	Proposed Uni- ed Framework
   Firmware variants per export market	One per market	Single shared codebase
   Effort to add a new grid code	Full re- design and re-certication	New parameter set in rule database
   Compliance margin per active code	High for design target, low other- wise	High for any se- lected code
   Maintenance of bug xes across markets	Must be repli- cated per variant	Applied once to shared function library
   Test automation reuse	Standard-specic scripts	Reusable, parameter-driven test sequencer

   Var, Frequency-Watt, and ride-through behavior, since these can be fully parameterized without algorithmic modication. Functions with more structurally different requirements across codes, e.g., the sign-convention difference in the treatment of reactive power in VDE-AR-N 4110 or the absence of a harmonic-order table in the German and Korean codes, require that the rule database also encode a small number of structural ags (e.g., sign convention, presence/absence of a given function) rather than purely numerical parameters. The proposed architecture supports this by allowing individual function blocks to be conditionally enabled or inverted polar- ity based on the active parameter set, rather than requiring separate code paths.

   The normalized comparison in Fig. 9 shows that a single- standard baseline design optimized for one grid code would be expected to have less compliance margin when its xed settings are checked against the requirements of a differet code for example, a controller tuned to the reactive power capability and ride-through settings of IEEE 1547-2018 would not, without modication, meet the wider ride-through voltage excursion or the load-referenced reactive power sign conven- tion of VDE-AR-N 4110 [32]. The proposed framework on the other hand by construction applies the parameter set cor- responding to the currently selected grid code and is therefore expected to retain full compliance margin for whichever code is active, at the cost of additional conguration-management complexity in the rule database and additional verication effort to certify each supported parameter set.

   From an engineering-economics viewpoint, the key benet of the proposed framework is that it reduces duplicated effort for control-software development and verication across ge- ographies. Instead of maintaining as many rmware variants as there are target markets, a manufacturer maintains one veried function library and a growing but comparatively low effort set of parameter les. The main expense is the extra effort needed for the design and verication of the generalized rule-database abstraction itself, and to make sure that no

   unintended interaction occurs among functions that are active simultaneously when parameters are changed.

9. CONCLUSION

This paper presented a systematic comparative study of three representative DER grid-interconnection codes, i.e., the IEEE 1547-2018, VDE-AR-N 4110, and the Korean DER

grid code, with respect to eleven functional dimensions in- cluding synchronization, reactive power, Volt-Var, Volt-Watt, Frequency-Watt, ride-through of voltage and frequency, anti- islanding, harmonics, and communication interoperability. The analysis led to the proposal of a generalized, congurable Unied Grid-Code Compliance Framework that decouples a common inverter hardware and control platform from a pa- rameterized, standard-specic rule database, allowing a single design to be recongured to meet multiple national grid codes. A generalized control ow, ride-through decision logic and an experimental verication methodology are presented in support of implementation and certication of the proposed framework.

The comparative, standards-based reasoning indicates that the proposed framework can go a long way in reducing the redundant rmware development and verication effort for manufacturers aiming at multiple geographies, while main- taining full compliance margin for each supported grid code. Future work, as shown in Fig. 10, includes expanding the rule database to additional national codes, incorporating cloud- based standards-update services, exploring AI-assisted param- eter auto-tuning, developing a digital-twin pre-certication testing capability, extending the framework to multi-inverter eet and virtual-power-plant coordination, and hardening the communication layer for cybersecurity in line with emerging smart-inverter interoperability requirements.

Fig. 9. Roadmap for evolution of the proposed framework toward an adaptive, self-certifying inverter platform.

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   TABLE VII

   Future Scope of the proposed Framework

   Direction	Description
   Additional grid codes	Extend rule database to other na- tional/regional DER codes
   Cloud-based updates	Remote, versioned distribution of up- dated parameter sets
   AI-assisted tuning	Automated parameter recommendation from eld performance data
   Digital-twin pre- certication	Simulation-based pre-validation prior to laboratory testing
   Fleet/VPP coordination	Multi-inverter coordination for micro- grid and virtual power plant operation
   Cybersecurity harden- ing	Secure communication consistent with smart-inverter interoperability standards

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