Converter-interfaced renewable energy system (CiRES) must operate reliably, yet dynamic and uncertain conditions, including external disturbances, circuit parameter variations, nonlinear loads, security threats, etc., often introduce strong nonlinearity and intermittency. Artificial neural networks (ANNs) are increasingly adopted to address these challenges and are widely applied in CiRES. This paper presents a structured overview of ANN applications across multiple domains in CiRES, including adaptive control, anomaly detection, energy and battery management, impedance identification, maximum power point tracking and power quality improvement. By organizing these applications in a modular CiRES framework, this review highlights cross-module interactions and points to opportunities for intelligent coordination and resilient system design under practical sensing and computational constraints.

Hybrid-bridge based dual-active-bridge (DAB) converter comprised of three-level (3L) and two-level (2L) full-bridge (FB) is promising to be a good candidate for medium voltage DC (MVDC) grids. By applying a corresponding modulation strategy proposed in this paper with multiple working patterns, a wide voltage conversion gain can be obtained. However, given that the conventional neutral-point-clamped (NPC) DAB converter has potential risk losing the control of the voltage conversion gain in backward and forward modes, an asymmetric active-neutral-clamped (A-ANPC) 3L structure is employed in the proposed converter to overcome this issue. Afterwards, to ensure a smooth working pattern transition, a simplified control strategy is proposed. The backflow power remains constant regardless of working conditions, and the zero-voltage-switching (ZVS) can be achieved for all power switches under the proposed modulation strategy. The operation principle, characteristics, and performances of the proposed converter are analyzed in detail and experimentally verified.

This paper proposes a modeling method for the input series and output parallel (ISOP) dual active bridge (DAB) converter under triple phase shift (TPS) modulation. Moreover, the reduced-order state-space average (RSSA) model is established to further obtain its equivalent small signal circuit model both for DAB and ISOP DAB converter. The model shows that the ISOP-DAB converter is a multi-input and multi-output (MIMO) system, the decoupling algorithm is adopted to convert the MIMO system to single-input and single-output (SISO) system, which is convenient for the control parameter design of the controller. Besides, the decoupled transfer function of ISOP system is approximately first order system. Finally, the correctness of the modeling method is validated by simulation in time and frequency domain.

Various DC circuit breakers (DCCBs) have been widely proposed for the DC fault protection of high-voltage direct-current (HVDC) grids. In recent years, hybrid DCCBs (HCBs) have been paid significant attentions due to their features of low power losses and fast dynamic response. However, several aspects regarding the design of HCB should be further addressed. For instance, the requirement of deploying a large surge arrester to dissipate the large fault current energy should be further addressed and the strategy to perform zero-voltage switching (ZVS) of semiconductor devices during the post-fault restoration processes should be investigated. In this paper, a dual-bridge hybrid DC circuit breaker (DB-HCB) with freewheeling diode branches is proposed to address the above issues. The operation principle of the proposed DB-HCB for pole-to-ground and pole-to-pole faults is presented. Compared with other HCBs, the capacity of the surge arrester is obviously reduced, so that the capital cost and volume of the proposed DB-HCB is decreased. Moreover, the ZVS is implemented during the post-fault restoration processes. Simulation results in PSCAD/EMTDC are given to validate the effectiveness of the proposed DB-HCB.

This paper proposes a zero-voltage and zero-current switching (ZVZCS) DC/DC converter characterized by 1) capacitive output and 2) input-series output-parallel (ISOP) structure for the high input voltage and high-power applications. The proposed converter can reduce the circulating current and duty cycle loss in comparison with the conventional converter with the inductive output. More significantly, the proposed converter can also effectively reduce the ripple current on the secondary clamping capacitor. Therefore, the proposed converter can improve the reliability of the secondary clamping capacitor. The characteristics and performances of the proposed converter are analyzed in detail. Finally, the simulation results verify the proposed converter.

This paper presents an optimization method of active and reactive power dispatch among multi-paralleled voltage source grid-connected inverters (GCIs) considering stability enhancement in low-frequency range. DQ impedance model of GCI with outer power control loop, inner current control loop and phase-locked loop (PLL) is first established. Then, effects of active and reactive power references on terminal impedance frequency characteristics of GCI, e.g., passivity, are theoretically derived. It's found that high active power reference tends to destabilize the power system, and high reactive power reference tends to stabilize the power system. On the basis of it, an active and reactive power dispatch method for stability enhancement in low-frequency range is proposed, where more/less active power and less/more reactive power are allocated to the GCIs with narrow/wide bandwidths of power control loop and PLL. Simulation is performed on a five-GCIs-based power system to validate effectiveness of the proposed active and reactive power dispatch method considering low-frequency stability enhancement.

This paper presents a reduced-order modelling method for grid-connected inverter (GCI) with long transmission cable (LTC). State-space models of GCI and LTC are first obtained from frequency characteristics of terminal impedance by applying vector fitting (VF) algorithm rather than conventional mathematical modelling. Then, Prony analysis (PA) and balanced truncation (BT) algorithms are employed to find an optimized order number of state-space model. Finally, a reduced-order model of GCI with LTC is established by removing non-dominant poles of original state-space model. Simulation results show that the proposed reduced-order modelling method is able to accurately obtain dominated poles of system, and reveal practical terminal impedance characteristics. The proposed method may simplify modelling procedure and improve computational efficiency for small signal stability analysis.

The modular multilevel converter (MMC) is attractive for medium-or high-power applications because of the advantages of its high modularity, availability, and high power quality. Reliability is one of the most important challenges for the MMC consisting of a large number of submodules (SMs). The capacitor monitoring in each SM of the MMC is an important issue, which would affect the performance of the MMC. This paper proposed an effective monitoring method for the capacitance in each SM of the MMC. The proposed method reveals the relationship between the arm average capacitance and the capacitance in each SM of the arm, which can be used for capacitance estimation with a simple algorithm. The simulation studies with the professional tool PSCAD/EMTDC are conducted with the proposed method. The study results show the effectiveness of the proposed method.

In this paper, an eigenvalue-based harmonic stability analysis method for offshore wind farm is proposed. Considering the internal cable connection layout, a component connection method (CCM) is adopted to divide the system into individual blocks as current controller of converters, LCL filters, collection system cable impedance, transmission cable impedance and grid impedance. By using this method, each block can be modelled independently and then be integrated into a whole state space matrix which contains sparse and diagonal matrix. Compared with the traditional state space formulation process, this method is superior in reducing the computational cost. A 4 by 4 wind turbines wind farm is selected as the study case and the proposed method is validated by comparing the results obtained from time domain simulation software - Power System Computer Aided Design (PSCAD).

The input capacitors' voltages are unbalanced under the conventional control strategy in a dual half-bridge cascaded three-level (TL) DC/DC converter, which would affect the high voltage stresses on the capacitors. This paper proposes a pulse-wide modulation (PWM) strategy with two working modes for the dual half-bridge cascaded TL DC/DC converter, which can realize the zero-voltage switching (ZVS). More significantly, a capacitor voltage balance control is proposed by alternating the two working modes of the proposed ZVS PWM strategy, which can eliminate the voltage unbalance on the four input capacitors. Therefore, the proposed control strategy can improve the converter's performances in: 1) reducing the switching losses and noises of the power switches; and 2) reducing the voltage stresses on the input capacitors. Finally, the simulation results are conducted to verify the proposed control strategy.

A novel topology is proposed for three-phase electric spring (TPES) to achieve specific functionalities. With respect to the existing one, the novel topology contains an additional three-phase transformer with the primaries located at the position of the non-critical three-phase load (NCL) of the existing topology and its secondaries connected to the new three-phase NCL, thus forming a new three-phase smart load (SL). To control the novel topology, the so-called modified δ control utilized for the single-phase electric springs is extended to the three-phase case. Thanks to these solutions, TPES exhibits a behavior entirely different from the existing ones. For instance, under a fluctuation of the line voltages, it exhibits a change of the voltages across NCL that has the same trend as the line voltages. Moreover, it regulates the voltages across the three-phase critical load even under both imbalanced and distorted grid conditions. The effectiveness of the novel TPES topology and of its control is validated by simulation results.

The modular multilevel converter (MMC) becomes attractive in the medium- and high-power application with high modularity. In this paper, the MMC is proposed to be applied in the variable speed wind turbine (VSWT) based on the full-scale back-to-back (BTB) power converter, where the generator-side converter is the three-level neutral-point-clamped (NPC) converter and the grid-side converter is the three-phase MMC. A control strategy is also presented for the MMC based VSWT for the second-order harmonic current elimination. The proposed MMC based VSWT and control not only mitigate the voltage ripple in the dc-link of the power converter to improve system performance, but also ensure the grid-side current balancing to increase the generated power of the wind turbine under the unbalanced grid fault, in comparison with the conventional VSWT based on BTB three-level NPC converters. The simulation studies of the proposed MMC based VSWT and control are conducted with a detailed PSCAD/EMTDC model, and the results show their effectiveness.

This paper addresses a state-space-based harmonic stability analysis of paralleled grid-connected inverters system. A small signal model of individual inverter is developed, where LCL filter, the equivalent delay of control system, and current controller are modeled. Then, the overall small signal model of paralleled grid-connected inverters is built. Finally, the state-space-based stability analysis approach is developed to explain the harmonic resonance phenomenon. The eigenvalue traces associated with time delay and coupled grid impedance are obtained, which accounts for how the unstable inverter produces the harmonic resonance and leads to the instability of whole paralleled system. The proposed approach reveals the contributions of the grid impedance as well as the coupled effect on other grid-connected inverters under different grid conditions. Simulation and experimental results are provided to verify the proposed harmonic stability assessment method.

This paper presents an eigenvalue-based harmonic stability analysis method for inverter-fed power systems. A full-order small-signal model for a droop-controlled Distributed Generation (DG) inverter is built first, including the time delay of digital control system, inner current and voltage control loops, and outer droop-based power control loop. Based on the inverter model, an overall small-signal model of a two-inverter-fed system is then established, and the eigenvalue-based stability analysis is subsequently performed to assess the influence of controller parameters on the harmonic resonance and instability in the power system. Eigenvalues associated with time delay of inverter and inner controller parameters is obtained, which shows the time delay has an important effect on harmonic instability of inverter-fed power systems. Simulation results are given for validating the proposed harmonic stability analysis method.