The Integrated Gate-Commutated Thyristors (IGCT) have active turn-off capability and serves as a key component in modern power electronic equipment. However, its turn‑off capability is limited, and forced turn‑off beyond the safe turn‑off threshold will easily lead to device damage. Therefore, online monitoring of the current flowing through IGCTs is of great engineering significance. Current sensors based on the tunneling magnetoresistance (TMR) effect are widely employed in compact current sensing applications, but they are restricted by magnetic saturation and thus cannot accurately measure kA-level high currents. This paper first analyzes the magnetic saturation characteristics and hysteresis effects of the magnetic core. By establishing a mathematical model of the internal magnetic flux distribution inside the core, the factors influencing core saturation and hysteresis in strong magnetic field environment are clarified, and the effects of various structural designs on magnetic flux distribution are investigated through finite element analysis. Based on this investigation, a discrete core–air gap structure with enhanced resistance to localized saturation and excellent linearity is proposed. Finally, experimental results demonstrate that compared with the traditional structure, the proposed structure reduces the volume by 83% and extends the measurement range from 4.6 kA to 10 kA. The influence of hysteresis on the waveform delay time is significantly reduced, which validates the effectiveness of the proposed method.

Flexible DC technology based on voltage source converters (VSCs) has become a promising solution for improving power quality, enhancing operational flexibility, and ensuring reliable power supply designed for metro step-down substations. This study proposes a novel flexible low-voltage DC power distribution system (LVDC-PDS) feeding scheme for metro substations and evaluates its technical feasibility and economic viability. A comprehensive design methodology is developed, covering system wiring configuration, IT grounding schemes, earthing resistance selection, electrical safety analysis, and protection measures. Coordinated control strategies for DC feeder voltage stabilizers and energy storage-assisted DC voltage regulation are implemented to maintain stable DC voltage. Simulation results demonstrate that the flexible LVDC-PDS maintains the 375 V DC feeder voltage within +/- 5%, while proper earthing-resistance design effectively limits fault currents to below 30 mA, meeting typical human-safety limits and ensuring personnel protection. Moreover, harmonics at the 5th, 7th, and 11th orders on the common 35 kV AC bus are effectively mitigated, delivering improved power quality compared with a conventional LVAC-PDS in metro substations. This work provides a practical and forward-looking pathway to enhancing power quality, electrical safety, and operational reliability for metro substations.

The line-commutated converter-based high-voltage direct current (LCC-HVDC) transmission technology is the primary choice for long-distance and high-capacity transmission. But there is an inherent risk of commutation failure (CF), which seriously threatens the safe and stable operation of the power grid. This article proposes a hybrid commutated converter (HCC) based on reverse blocking integrated gate-commutated thyristor (RB-IGCT), which can completely solve the problem of CF. Firstly, the topology design and control methods of HCC are introduced. On this basis, key technological breakthroughs, including voltage equalization design, saturable reactor optimization, and reactive power optimization are introduced separately. Detailed experiments, including synthetic circuit operation tests and system operation tests, have verified the reliability of HCC technology. HCC technology will be applied to the renovation project of China’s Lingbao converter station in September 2025.

The variable and unpredictable nature of renewable energy creates operational difficulties for off-grid hydrogen production systems seeking economic viability. To address this issue, this research introduces an innovative sizing methodology for off-grid hydrogen production systems, integrating probabilistic scenario analysis and load-follow-source coordination control technique. First, a scenario generation method is employed to identify representative operational scenarios of renewable energy. Second, a load-follow-source control strategy considering the multimodal conversion of alkaline electrolyzers and proton exchange membrane electrolyzers is developed. Subsequently, a optimization model of capacity configuration is formulated, with the objective of minimizing the levelized cost of hydrogen (LCOH), maximizing system operation efficiency, and minimizing the rate of abandoned for renewable energy. An improved generalized normal distribution optimization algorithm is introduced to solve the optimization model. Compared with the existing methods, the load-follow-source strategy proposed in herein achieves a higher hydrogen production rate and has better multi-mode operation flexibility. Meanwhile, the capacity optimization configuration method demonstrates good economic and efficiency performance, that is, the LCOH and the rate of abandoned are the lowest, reaching 19.4 ¥ /kg and 4.5% respectively, and the system operation efficiency is the highest at 89.9%. The researches furnish foundational principles for orchestrating autonomous hydrogen synthesis systems.

Scaling high-altitude wind energy systems (HAWESs) to the megawatt level faces a “weight-voltage” paradox: reducing tether mass requires medium voltage, yet conventional voltage-boosting components add prohibitive airborne mass. This paper resolves the paradox with a novel architecture using series-connected, diode-rectified generators, which inherently builds medium transmission voltage without onboard converters or transformers, enabling an ultralight airborne system controlled solely by a grid-side converter (GSC) located on the ground. A small-signal stability analysis considering generator parameter heterogeneity reveals that the system is robust to moderate wind variations, but becomes unstable when wind-speed heterogeneity drives a turbine into a region of positive torque-speed slope. The precise identification of this physical stability boundary provides the crucial design guidance needed to unlock a practical pathway toward the deployment of utility-scale HAWESs.

The commutated converter constructed by fully- controlled integrated gate-commutated thyristors (IGCT) has active turn-off capability, enabling forced commutation to resolve commutation failure. However, their turn-off capacity is limited, and active turn-off above the maximum turn-off current may damage itself, so it is essential to detect the current of the IGCT online. Traditional current sensor based on tunneling magnetoresistance is susceptible to errors caused by the nonuniform magnetic fields in the valve. This article analyzes the distribution pattern of the magnetic field in the valve and establishes a mathematical model of magnetic field change in the magnetic core air gap under nonuniform magnetic field, clarifies the main factors affecting the consistency of the sensor outputs, analyzes the transient interference generated by the active turn off of the IGCT. Combined with the magnetic field distribution results from COMSOL finite element simulation, an anti-interference design method is proposed to achieve high consistency measurement of IGCT current. Finally, experimental tests show that the maximum error of the air-gap magnetic field caused by conductor offset and copper busbar influence is reduced from 11.14% of the traditional structure to 0.69%, and the transient interference during active turn-off is greatly reduced, which verifies the effectiveness of the proposed method.

The integration of distributed generators, combined with the resistive characteristics and low short-circuit capacity (SCC) of feeders, can lead to voltage and power oscillations in distribution networks. This study investigates the dynamic behaviours of such systems, identifies the causes of these oscillations, and proposes two fluctuating power allocation strategies using advanced flexible interconnection devices (FIDs). An FID consists of multiple coordinated voltage source converters (VSCs) and regulates AC voltages to maintain stable system operation. Two representative scenarios are investigated: 1) a flexible interconnected distribution network with normal feeder connections; and 2) a network incorporating low-SCC feeder connections. The proposed strategies perform: 1) coordinated power adjustment and sharing between FID-VSCs and feeders to mitigate active power fluctuations, with each converter controller adjusting its output based on available capacity; and 2) minimizing feeder voltage oscillations and stabilizing system operation through coordinated reactive power support from the FID, while accounting for feeder SCC limits. An FID-enabled 10 kV flexible distribution network with a wind generator is modelled in PSCAD/EMTDC to validate the strategies, demonstrating continuous and steady operation, as well as appropriate power allocation under different conditions. The results show that, the proposed strategies increase converter utilization, improve active power transfer capability, and reduce voltage and power oscillation risks.

Hybrid commutation converters (HCCs) utilizing reverse-blocking integrated gate commutation thyristors (IGCTs) have gained significant attention due to their immunity to commutation failure. Leveraging the recovery enhancement characteristics of IGCTs, HCCs demonstrate superior performance at reduced extinction angles, thereby minimizing reactive power consumption. This study presents a comprehensive investigation into reactive power control strategies for HCCs operating at small extinction angles. First, the topological configuration and commutation principle of HCC are elucidated. Subsequently, the mechanism of HCC reactive power control is analyzed, and a reactive power control strategy is proposed by combining the converter transformer taps with extinction angles. Moreover, the relationship between transformer taps and reactive power exchange under different rated extinction angles is calculated, and the theoretically rated extinction angle is proposed. Finally, to validate the proposed control strategy, a four-terminal ultra-high voltage direct current power grid incorporating HCC technology is modeled and simulated using PSCAD/EMTDC. The simulation results demonstrate that the proposed strategy effectively supports AC systems by reducing reactive power absorption in HCCs, while simultaneously exhibiting enhanced reliability and economic efficiency.

Urban Railway Transit Power Supply System (URTPSS) involves power quality problems related to reactive power and harmonics. In addition to this, it is susceptible to multi-system resonance at specific frequencies. Negative impedance caused by capacitive characteristics carries the risk of harmonic amplification, which may lead to equipment damage and instability within the metro substation system. This paper analyzes the monitored profile of the real-world “SHL” metro substation and identifies the capacitive harmonics of the 35kV AC bus. A theoretical analysis is performed and a dynamic model of a Metro Traction Step-Down Substation (MTSDS) is developed to study capacitive harmonics and their potential causes, and to analyze the network impedance across multiple frequencies. Following that, a Distribution Static Synchronous Compensation (DSTATCOM) solution is proposed, featuring a 35kV-10MVar power stage configuration and its associated controller design. The improved instantaneous power controller utilizes the inner α-coordinate current loop to suppress harmonic magnitudes and reconstruct the capacitive impedance. The β-coordinate current is utilized to regulate reactive power demand and correct the system power factor. Simulation results performed in the PSCAD/EMTDC and RSCAD/RTDS environments validate the effectiveness of the DSTATCOM solution with the improved controller under steady-state and load-changing operating conditions.

Due to the limitation of the recovery characteristics of thyristors, the minimum extinction angle of traditional line commutated converter based high voltage direct current (LCC-HVDC) system is generally 12 degrees, which requires the system to be equipped with expensive and large reactive power compensation equipment. Hybrid commutated converter (HCC) based on reverse blocking integrated gate commutated thyristor (RB-IGCT) with better recovery characteristics can operate at ultra-low extinction angle. This article first conducts an in-depth mechanism study on the recovery process of RB-IGCT under HCC conditions. Then, the differences in the recovery process of RB-IGCT under different conditions are analyzed through experimental design. On this basis, a 6-RB-IGCTs component and a +/- 10 kV/1 kA HCC system are designed. The ability of RB-IGCT to operate with low reactive power has been fully verified through component level experiments and system level experiments. Finally, the reactive power optimization capability of HCC operating at ultra-low extinction angle is analyzed through PSCAD/EMTDC simulation calculation. The application of RB-IGCT with better recovery characteristics in HCC is of great significance for optimizing reactive power configuration in HVDC systems.

This paper proposes a novel dual-loop Active Disturbance Rejection Control (ADRC) framework tailored for Hybrid Line Commutated Converter (HCC) HVDC systems. Unlike conventional Line-Commutated Converter (LCC) systems, which depend on passive commutation and fixed extinction angle control-resulting in limited flexibility and susceptibility to grid perturbations-HCC systems with IGCT enable independent and precise regulation of the extinction angle, which diminishes the necessity of adhering to a fixed extinction angle, exposing the limitations of traditional control strategies in fully exploiting HCC capabilities. To address this, the proposed dual-loop ADRC controller integrates DC voltage regulation with extinction angle management within a unified framework, achieving dynamic optimization of both parameters. This approach enhances disturbance rejection and system stability, offering superior performance over conventional methods. Validated through Matlab simulation, this study represents a significant step forward in advancing control methodologies.

Commutation failure (CF) is an inherent problem faced by line commutated converter high voltage direct current (LCC‐HVDC) technology. To completely solve the problem of CF, we have proposed a novel hybrid commutated converter (HCC) technology based on reverse blocking integrated gate commutated thyristor, which can utilise two methods for commutation: enhanced grid voltage commutation and active turn‐off forced commutation. In this paper, the topology and operating principle of HCC are proposed. Then, the control and protection strategy is designed based on the current variation trend under AC faults. To verify the effectiveness of HCC in mitigating CF, a 120‐kV/360‐MW HCC‐HVDC model is built in PSCAD/EMTDC, adopting LCC at the rectifier side and HCC at the inverter side. Based on this model, HCC steady‐state and fault transient stresses are analysed. Various AC faults are simulated and the performance of HCC‐HVDC is compared with LCC‐HVDC. Finally, the results show that the HCC topology and proposed control strategy can solve CF under all fault conditions with almost the same attributes as LCC, such as large capacity, low cost, low loss and high reliability, which is meaningful for the application of HCC to the HVDC transmission system.

The modular multilevel converter (MMC) has become increasingly important in voltage-source converter-based high-voltage direct current (VSC-HVDC) systems. Direct and indirect modulation are widely used as mainstream modulation techniques in MMCs. However, due to the challenge of quantitatively evaluating the operation of different modulation schemes, the academic and industrial communities still hold differing opinions on their performance. To address this controversy, this paper employs the state-of-the-art computational methods and quantitative metrics to compare the performance among different modulation schemes. The findings indicate that direct modulation offers superior modulation potential for MMCs, highlighting its higher ac voltage output capability and broader linear PQ operation region. Conversely, indirect modulation is disadvantaged in linear modulation, which indicates inferior output voltage capability. Furthermore, this paper delves into the conditions whereby direct and indirect modulation techniques become equivalent in steady-state. The study findings suggest that the modulation capability of direct modulation is the same as that of indirect modulation in steady-state when additional controls, including closed-loop capacitor voltage control and circulating current suppression control (CCSC), are simultaneously active. Simulation and experiments verify the correctness and validity.

The commutation characteristics of hybrid commutated converter (HCC) in high voltage direct current (HVDC) transmission system during different faults are studied in this paper. Firstly, the commutation process of line commutated converter (LCC) is analyzed, and the basic causes and countermeasures of commutation failure is figured out from the perspective of operation principle. Secondly, according to the principle of HCC, the grid commutation and active commutation working modes of HCC are analyzed, then the timing cut-off and current rising cut-off strategies are designed for the active commutation working mode. Finally, the simulation research is carried out based on CloudPSS. Through the simulation research of LCC and HCC commutation process under different fault conditions, the commutation characteristics of HCC during fault and its influence on grid are analyzed. The simulation results show that HCC absorbs less reactive power during the fault, which can support the grid voltage recovery to a certain extent, and compared with LCC, HCC has no additional impact on the grid.

The integration of flexible interconnection devices (FIDs) into distribution networks introduces complexities in power flow management under both normal and transient/fault conditions, thereby decreasing the selectivity, sensitivity, and reliability of common current protection schemes. This article examines the impact of FIDs on existing current protection arrangements and proposes a novel method for recalculating the overcurrent protection setting. The AC output characteristics of the FID for a short period after AC fault occurrence are first investigated. It is followed by an analysis of FID's impact on the three-stage current protection scheme in flexible interconnected distribution networks, conducted through theoretical calculations in MATLAB and simulations in PSCAD/EMTDC. A quantitative assessment of the mal-operation and non-operation of current protection caused by FIDs of varying capacities, power flow directions, and locations, with a focus on the typical 10 kV 10MVA FID, is also performed. Based on the above findings, a calculation and modification method for Stage III overcurrent protection setting is presented to address mal-operation issues in FID-based distribution networks, with its feasibility validated through electromagnetic transient simulations.

Increasing the allowable capacitor voltage ripple is a highly effective approach to significantly decrease the necessary submodule capacitance in a modular multilevel converter (MMC). However, the existing techniques for low-capacitance high-ripple MMC (HR-MMC) exhibit drawbacks like a rise in the number of required submodules (SMs) and a decrease in the operating range. This paper proposes an improved design methodology for HR-MMC that aims to mitigate these limitations. Firstly, the proposed methodology introduces an over-insertion approach to avoid the increase in the number of SMs. Secondly, whole-operating-range linear modulation (WOR-LM) and maximum selectable valve-side ac voltage (MS-ACV) are introduced as key constraints for determining the optimal allowable ripple rate. Furthermore, by considering the capacitor voltage ripple effect (CVR effect) and circulating current suppression control (CCSC), a precise calculation of the reference waveform function (RWF) can be achieved. This analysis allows for the investigation of how an increase in the high ripple factor (HR factor), which signifies the increased level of the allowable ripple rate, impacts WOR-LM. It is discovered that the MMC can maintain WOR-LM without reducing the MS-ACV until the HR factor reaches an inflection point. By setting this newly determined inflection point as the optimized HR factor, HR-MMC can minimize its energy storage requirement without increasing the number of SMs and reducing the operating range. The theory is verified by simulated and experimental results and compared with the existing solution.

In view of the problem of successive commutation failure in multi-infeed direct current systems, this paper investigates the commutation characteristics of hybrid commutation convert technology and its application in mitigating successive commutation failure, with a case study based on the Lingbao Converter Station modification project in the Henan grid. First, the operational mode of hybrid commutated converter is proposed, and its low reactive power consumption reduced by 20% is calculated and compared with that of a line commutated converter. Then, the mechanism of successive commutation failure in Henan grid is analyzed using an equivalent grid model. The hybrid commutation convert technique is introduced as a solution to successive commutation failure due to its advantages, including complete commutation failure mitigation, fast post-fault recovery, and reduced reactive power consumption. Finally, the effectiveness of the proposed operational mode is verified through Real-Time Digital Simulator simulation tests. A simulation model of both hybrid commutation converter and line commutation converter-based high voltage direct current system is developed, and the commutation characteristics during fault and recovery are analysed. Additionally, the efficacy of hybrid commutation converter in suppressing successive commutation failure in the multi-infeed direct current system is evaluated through CloudPSS-based grid simulations.

With the rapid development of renewable energy, new types of loads and power electronic technology, the construction of DC distribution system on the basis of AC distribution network is becoming the future trend in distribution network development. The choice of grounding method significantly impacts the system’s security, reliability and economy. The grounding method for DC system is influenced by many factors, such as converter topology. Currently, there is no unified method for the grounding design of DC system, and the grounding methods of various demonstration projects in China differ. The purpose of this paper is to study the grounding methods of DC power distribution systems based on modular series two-level converters, including AC-side grounding and DC-side grounding. By constructing a system model and combining with simulation analysis, this study explores the impact of different grounding methods on harmonic voltage, current, and fault conditions of the system to provide a reference for designers.

AbstractThe flexible interconnection device (FID) offers significant advantages for interconnecting different distribution networks flexibly. This paper focuses on the significant advantages offered by the FID for interconnecting different distribution networks flexibly. It specifically delves into FID‐based multi‐voltage and multi‐substation distribution networks, proposing a preferable scheme applicable to major load‐centred cities. Beginning with an analysis of constructed FID‐based flexible interconnected distribution network projects, key configurations and features are summarized. Subsequently, typical configurations, electrical parameters, facilities, relevant power functionalities, and application scenarios of multi‐voltage multi‐substation distribution networks are outlined. Building upon this foundation, a suitable interconnection scheme tailored for current urban use is explored to meet the specific needs of load‐centred cities, while incorporating recent advancements in high‐power‐density IGCT technology. An EMT model of a 10 kV/10 MW IGCT‐based four‐substation distribution network is developed in PSCAD/EMTDC. Through thorough analysis under different conditions, the operational performance and benefits are evaluated, providing insights into the efficiency and resilience of the proposed FID‐based interconnection. Lastly, challenges and prospects are discussed from various perspectives to advance the development of FID‐based flexible interconnection solutions. This study aims to contribute to the advancement and implementation of robust interconnection solutions to meet the evolving needs of major load‐centred cities.