Rapid growth of converter-interfaced renewable energy sources has made the estimation of system inertia increasingly complex, as virtual inertia control (VIC) introduces nonlinear and time-delayed dynamics that traditional methods often overlook. This article proposes a data-driven framework for online estimation of effective inertia under varying wind power penetration (WPP) and VIC gains. The approach integrates wavelet-based denoising, Isolation Forest-based onset detection with an optimally tuned decision threshold, robust rate of change of frequency estimation, and an Attention-Augmented Encoder–Decoder Architecture model for accurate estimation of net power imbalance. Unlike existing data-driven methods, the proposed framework explicitly accounts for the activation delay and nonlinear response of VIC, yielding superior robustness across diverse operating conditions. Extensive simulations are conducted on a modified 11-bus and the truncated model of Indian Eastern Regional Grid system, considering a wide range of disturbance magnitudes, WPP levels, and VIC gains. Further, the framework is shown to be scalable for area-level inertia estimation in large systems by leveraging boundary bus frequency and tie-line power flow.

A multi-energy system (MES) is an integrated energy infrastructure that simultaneously models and optimizes the coupling and conversion processes among multiple energy carriers (e.g., electricity, thermal energy, and hydrogen, etc.) across diverse end-use sectors, enabling coordinated operation for improved efficiency, flexibility, and sustainability. Integrating renewable energy sources (RESs) into MES systems drives the adaptation of energy storage systems (ESSs) and the development of strategies to mitigate their intermittency. Indeed, this paper provides a sophisticated model of dispatchable ESSs in integrated energy hubs, demonstrating how storage units optimize the operational cost of combined heat and power (CHP) systems by jointly accounting for renewable generation and energy buffer states. The proposed controller employs relaxed model predictive control (RMPC), reducing computational time by managing complex decision variables more efficiently than standard MPC, making it suitable for residential energy management. Numerical simulations confirm that the control strategy effectively operates the integrated system, meeting constraints, and demands while minimizing device costs and maximizing profits.

The Virtual Synchronous Generator (VSG) represents a promising grid-forming (GFM) control approach that emulates the dynamic characteristics of synchronous generators through the implementation of virtual inertia and damping. This paper investigates the influence of including the inner current control and the current reference angle on the transient stability of VSG. While incorporating current control into the stability analysis improves the accuracy of the results, it also results in a reduced domain of attraction (DoA) for the system. To address these limitations, this paper proposed an advanced control strategy, which incorporates the standard VSG with additional feedback and feedforward functions to enhance VSG transient stability by expanding DoA. Numerical simulations demonstrate that the proposed control surpasses conventional VSG methods in terms of adaptability, stability, and reliability under various disturbances, such as three-phase faults and load increases.

Microgrids (MGs) with distributed energy resources (DERs) provide significant benefits in terms of energy efficiency and sustainability. However, they bring challenges to protection schemes, particularly relay settings and coordination. This article investigates the deployment of directional overcurrent relays (DOCRs) in MGs. Given the limited inertia of DERs and the potential instability resulting from extended DOCR operating times postfault, a novel DOCR setting is proposed. This setting uses shifted user-defined characteristics that integrate two inverse curves to ensure relay coordination and MG stability. Meanwhile, recognizing that MGs can operate in various topologies, a single DOCR setting may prove ineffective for many scenarios. Therefore, this article configures DOCRs with adaptive settings to manage diverse operating conditions. Due to the limited number of settings supported by commercial DOCRs, a self-organizing map is used to categorize MG potential scenarios into coherent groups aligned with available DOCR settings. The stability-constrained settings of each DOCR are optimized using the genetic algorithm and then stored within the relay for seamless activation when needed. The efficacy of the proposed approach is evaluated on a modified IEEE 33-bus system with synchronous and inverter-based DERs using DigSILENT and MATLAB.

In this article, we propose an improved high-boost-gain split-source inverter (SSI) for renewable energy generation. The proposed inverter retains the features of the existing SSIs, such as single-stage boost inversion with a reduced number of passive components and elimination of the inverse modulation–duty relationship constraint of the impedance-source inverters. It also provides additional features that include higher boost inversion ability than existing SSIs to connect low-voltage renewable energy sources to the grid, no voltage-source short-circuit issue, which increases the robustness of the proposed inverter and pulsewidth modulation dead times can be relieved, and the negative input dc-terminal and ac-neutral are electrically connected in the proposed inverter, resulting in a constant common-mode voltage and elimination of leakage ground currents for grid-interfaced PV power systems. A detailed circuit operation and analysis is provided, and experiments are performed on a 400-VA prototype inverter to confirm the working of the proposed topology.

A new type of filter/extractor named independent time-delay signal cancellation (itDSC) method is proposed in this article. Unlike conventional harmonic sequence filter (HSF) designs, the phase modifying and vector recovering stages of the proposed itDSC are separately set with single targets to make time-delays independent from the targeted HS indices and fundamental period. Consequently, the proposed HSF is more flexible in design, more robust and accurate in performance as well as faster in dynamic response compared to the conventional ones. A new phasor representation of an arbitrary order and sequence is first introduced for three-phase signals by using only a single integer-index-number (h). Then, a generalized principle of filtering/extracting arbitrary HS is proposed where the conventional time-dependent methods are specific cases. Last, new designs with independent time-delays are proposed to avoid the drawbacks of dependent time-delays and improve the filter performance in the applied systems. Comparative performance and extended applications on fundamental-frequency positive-sequence extraction used in power converter control areas are presented. The experiments show the superiority, application potentials, and challenges of the proposed method in the power converter control area.

Single-phase dual-buck ac–ac (DBAC) converters are gaining attention due to their intrinsic protection from shoot-through and open-circuit problems of conventional ac–ac converters. However, research works on DBAC converters are mainly concentrated around unipolar topologies. In a few developed bipolar topologies to date, the inverting buck–boost operations (for series voltage injection and step-variable frequency outputs) are inefficient and burdened by large voltage and current stresses (${v}_{\text{in}} + {v}_o\ \text{and}\ {i}_{\text{in}} + {i}_o$) of switching devices and ripples of passive elements. In this article, an efficient dual-buck structured buck–boost ac–ac converter is proposed, with the following features: no voltage source shoot-through and inductor open-circuit problems, natural attainment of safe commutation without additional protection circuitry or complex control, no need for pulsewidth modulation dead times, and elimination of high-frequency conduction ofmosfet’s body diodes and related slow reverse recovery issues. The proposed converter provides distinct types of efficient inverting and noninverting buck and boost operations, with smaller switch voltage/current stresses (${v}_{\text{in}}/{v}_o$and$\ {i}_{\text{in}}/{i}_o$) and passive component ripples. Combined inverting and noninverting buck–boost operations are also proposed with separate tuning of buck and boost voltage transfer ratios. A simple adaptable switching strategy provides the switch control pulses for all circuit operations by modulating the buck and boost control reference signals. The proposed converter provides sustained input/output currents and performs well with nonresistive loads. Extensive theoretical analysis is presented followed by practical verifications on a 400-VA laboratory circuit.

The output voltage of a photovoltaic panel is greatly affected by irradiance, temperature, shading, etc. A buck-boost type inverter is, therefore, required to accommodate the wide fluctuations in dc voltage. This article proposes a class of single-phase, single-stage buck-boost inverters employing five switches (implemented using power MOSFETs with external fast recovery diodes) to provide buck-boost operation for wide variations in photovoltaic (PV) output voltage. In this article, the proposed inverters are immune from current shoot-through problems associated with voltage source inverters, easing the requirement for PWM dead-times. They also provide a common-grounding feature between the grid-neutral and the negative-terminal of the PV panel, successfully suppressing the PV leakage current. In addition, they provide reactive power support. A simple input boost inductor-based buck-boost inverter is proposed with a wide gain range; other variants are also proposed based on the switched inductor, quadratic boost, and switched coupled-inductor, achieving higher boost voltage inversions with smaller values of duty ratio. Detailed circuit operations are presented based on proposed modulation strategies. Design guidelines/requirements of components and their comparisons are provided for all of the proposed inverters. The theoretical analysis and performance characteristics of all four topologies are experimentally validated using 400 VA laboratory prototype inverters.

DC short-circuit fault ride through is one of the most important characteristics for the modular-multilevel converters (MMC) employed in high-voltage direct-current (HVdc) transmission systems. During the faults, for providing a fault-tolerant control with reactive power compensation to the grid, the MMC normally changes its structure, which requires a remarkable modification and burden computation for implementing the modulation technique in the MMC. This paper proposes an alternative submodule configuration of the MMC based on a carrier-phase-shift PWM scheme, which is easily implemented for switching the operation modes of the MMC from normal condition to fault-tolerant control. The arms of the proposed MMC are configured by typical half-bridge submodules (HBSM) and suggested series-connected triple SMs (SCTSM) in interleaving series, where the SCTSM is composed of three HBSMs connected in series through an additional IGBT and a clamp diode. With the additional IGBTs and diodes, the SCTSMs can produce bipolar output voltages and the MMC can be restructured to operate as three-phase cascaded multilevel converter during pole-to-pole short circuits to control the converter currents. In addition, the cost and power loss of the proposed MMC are lower than those of the existing MMCs based on full-bridge SMs (FBSM), a hybrid of HBSMs and FBSMs, and clamp-double SMs. PSIM simulation results for the 300 MW-300 kV HVdc system with the proposed MMCs are shown to verify the effectiveness of the scheme.

In this paper, a new configuration of modular-multilevel converter (MMC) is proposed, which is the modified structure of the alternative-arm converter (AAC) with the improvements in terms of cost, loss, footprint, and device count. The proposed MMC also operates through alternatively conducting and blocking the upper and lower arms in a leg as the AAC, where a common stack of full-bridge submodules (FBSM) is shared for the upper and lower arms. This results in a reduction of the SM number in the converter leg, consequently for the whole MMC, from which the number of DC capacitors of the SMs is also reduced resulting in a significant reduction in cost and volume of the converter and improving the reliability of the converter. Extra active switches are required to control the common stack to operate with either the upper or lower arms. Furthermore, the proposed MMC also provides the fault-handling capability and reactive power compensation to the electric grid under the DC-cable short circuits. Simulation results for a 17-level MMC modeled by PSIM have been shown to verify the feasibility of the proposed scheme under normal operation and DC-fault conditions.

This paper introduces a novel framework of coordinated voltage and frequency control strategy for islanded microgrid (MG) operation. The proposed control schemes rely on local measurements as communication-free control approach. Therefore, the distributed controllers of the MG components have been deployed based on their slow, medium, and fast dynamic responses to maintain the voltage and frequency in adherence to IEEE Standards 1547 and 929. The various voltage and frequency control responses associated with reactive power management scheme are efficiently utilized based on well-defined states of operation and transient management scheme. In each state, the roles of each device for voltage and frequency regulations are defined with its regulation capability, and response time based on its local measurements. Consequently, the fast reactive power compensation and rapid frequency regulation are ensured based on the inverter-based devices at challenging operating conditions. As a result, the proposed control strategy improves the voltage and frequency regulation, transient response, and MG stability. A comprehensive simulation study has verified the superior performance of the communication-free approach during steady state and in response to severe disturbances.

New grid codes impose fault ride through (FRT) requirements on large doubly fed induction generator (DFIG)-based wind parks connected to transmission systems in order to reduce the loss of huge generation power due to temporary faults. Recently, the focus is set toward the development of different wind turbine technologies to enhance the FRT capability of wind parks with no consideration for transmission system protection schemes. This paper proposes a new communication-based dual time-current-voltage (Dual-TCV) tripping characteristic for directional overcurrent relays (DOCRs) that considers the FRT capability of wind parks by taking fast fault isolation actions in transmission systems. The protection coordination problem is formulated and solved to determine the optimal relay tripping settings. The proposed approach is tested on the IEEE 24-bus transmission system with up to eight DFIG-based wind parks. The outcome of this study reveals that protection schemes based on DOCRs governed by the proposed Dual-TCV tripping characteristic ensures fast fault isolations that significantly enhances the FRT operation of wind parks in adherence to grid code requirements. The transient analysis verifies the superior performance of the proposed protection approach in enhancing the FRT operation of wind parks.

DC Microgrids (MGs) are increasingly popular in recent years to support distributed generation based power systems. This paper focuses on the improvement of the load sharing control strategy and presents a decentralized control scheme, namely improved digital average current sharing (IDACS). Compared to the conventional hierarchical droop control scheme, the IDACS shows the structural difference and demonstrates the advantages of high modularity, automatic load sharing, low current deviation, and robust voltage regulation. In the proposed IDACS scheme, each primary converter includes both current controller and voltage controller to compensate voltage uniformity, which is caused by droop control scheme. Based on the foundation of digital average current sharing (DACS), a comprehensive approach is developed to design controllers for DC-DC converters by using anti-windup strategies. The improved performance is validated by simulation and demonstrates low voltage regulation and fast recovery time.

Microgrid (MG) research mainly focuses on AC-based power flow control techniques. Nevertheless, the rise of DC output sources such as photovoltaic (PV) systems, fuel cells, and distributed batteries leads to the immediate need for DC MGs. In this paper, a hierarchical control strategy for a droop-controlled DC MG is proposed, which fits the smart house infrastructure to adopt online renewable generation and load sharing. The improved control strategies combined with the hierarchical approach includes three loops of controllers: the primary control, the secondary control, and the tertiary control. The issues of internal current limiter and anti-windup are also discussed in this study. The simulation results of the proposed approach are presented to verify the feasibility, and the experimental results are carried out to evaluate the droop concept and secondary voltage compensation.

This paper addresses implementation issues associated with a novel damping control algorithms for STATCOM and SSSC (static synchronous series compensator) in a series compensated wind park for mitigating SSR (subsynchronous resonance) and damping power system oscillations. The IEEE first benchmark model on subsynchronous resonance is adopted with integrating aggregated self-excited induction generator based wind turbine to perform the studies. The potential occurrence and mitigation of the SSR caused by induction generator effects as well as torsional interactions, in a series compensated wind park are investigated. The auxiliary subsynchronous damping control loops for the STATCOM and SSSC based on a novel design procedure of nonlinear optimization are developed to meet the damping torque in the range of critical torsional frequencies. The performances of the controllers are tested in steady state operation and in response to system contingencies, taking into account the impact of short circuit ratios (SCRs). Simulation results are presented to demonstrate the capability of the controllers for mitigating the SSR, damping the power system oscillation and enhancing the transient stability margin in response to different SCRs.