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Abstract The rapid development of offshore wind farms (OWFs) calls for economical and reliable power transmission technology. This review paper focuses on the diode‐rectifier‐unit based high voltage direct current (DRU‐HVDC) transmission systems. The main technical features of DRU‐HVDC are highlighted and the comparisons with MMC‐HVDC and LCC‐HVDC are conducted. Considering the uncontrollability of DRU and the necessity of offshore wind turbines (WTs) to establish offshore network, the existing decentralized and centralized control strategies are reviewed in detail. For the fully‐grid‐forming converter, the operation principle of the P–V and Q–f power control is explained from the OWF‐DRU level and the WT level, respectively. For the partial‐grid‐forming converter, why the voltage control loop can be eliminated is analysed. Focusing on the start‐up issue caused by the unidirectional‐power‐flow characteristic of DRU, several start‐up solutions are reviewed, including medium voltage alternative current (MVAC) umbilical cable, auxiliary MMC, energy storage for WTs, auxiliary low voltage DC cable. Then considering different fault locations, the fault characteristic and protection of the DRU‐HVDC system is presented, including the offshore AC faults, DRU faults, HVDC faults and onshore AC faults. Finally, the future research topics worth exploring for DRU‐HVDC system are identified.

Abstract Constrained by the AC voltage amplitude modulated by a modular multilevel converter‐based static synchronous compensator (MMC‐STATCOM), its reactive power output may be subject to oscillations under grid contingencies, posing a threat to the grid stable operation. To solve this problem, this paper proposes a variable DC voltage (VDCV)‐based reactive power enhancement scheme for MMC‐STATCOM. In this scheme, a novel variable DC voltage control is designed, which can increase the DC voltage in a transient state for relaxing the constraint of the AC voltage amplitude modulated by MMC‐STATCOM and improving its reactive power output capability (RPC). At the same time, to make full use of the improved RPC of MMC‐STATCOM, a VDCV scheme also proposes an optimisation algorithm of its reactive current‐AC voltage droop coefficient using the established reactive power model of the MMC‐STATCOM. Based on small signal modelling and analysis, the key parameters of the proposed VDCV scheme are optimised. The performance and reactive power enhancement of the VDCV scheme is evaluated through the hardware‐in‐the‐loop experiment under grid disturbances.

With large-scale grid integration of renewable energy sources (RES), power grid operations gradually exhibit the new characteristics of high-order uncertainty, leading to significant challenges for system operational security. Traditional model-driven generation dispatch methods require large computational resources, whereas the widely concerned Reinforcement Learning (RL)-based methods lead to issues such as slow training speed due to the high complexity and dimension of processed grid state information. For this reason, this paper proposes a novel Grid Expert Strategy Imitation Learning (GESIL)-based real-time (5 min intervals in this paper) dispatch method. Firstly, a grid model is established based on the graph theory. Secondly, a pure rule-based grid expert strategy (GES) considering detailed power grid operations is proposed. Then, the GES is combined with the established model to obtain a GESIL agent using imitation learning by offline–online training, which can produce specific grid dispatch decisions for real-time. By designing a graph theory-based grid model, a model-driven purely rule-based GES, and embedding a penalty factor-based loss function into IL offline–online training, GESIL ultimately achieves high training speed, high solution speed, and strong generalization capability. A modified IEEE 118-node system is employed to compare the proposed GESIL to traditional dispatch method and RL method. Results show that GESIL has significantly improved computational efficiency by approximately 17 times and training speed by 14.5 times. GESIL can more stably and efficiently compute real-time dispatch decisions of grid operations, enhancing the optimization effect in terms of transmission overloading mitigation, transmission loading optimization, and power balancing control.

Abstract Rheumatoid arthritis (RA) is a systemic autoimmune disorder characterized by excessive proliferation of rheumatoid arthritis synovial fibroblasts (RASFs) and accumulation of inflammatory cytokines. Exploring the suppression of RASFs and modulation of the RA microenvironment is considered a comprehensive strategy for RA. In this work, specifically activated nanoagents (MAHI NGs) based on the hypoxic and weakly acidic RA microenvironment are developed to achieve a second near‐infrared fluorescence (NIR‐II FL)/photoacoustic (PA) dual‐model imaging‐guided multi‐treatment. Due to optimal size, the MAHI NGs passively accumulate in the diseased joint region and undergo rapid responsive degradation, precisely releasing functionalized components: endogenous melanin‐nanoparticles (MNPs), hydrogen gas (H2), and indocyanine green (ICG). The released MNPs play a crucial role in ablating RASFs within the RA microenvironment through photothermal therapy (PTT) guided by accurate PA imaging. However, the regional hyperthermia generated by PTT may exacerbate reactive oxygen species (ROS) production and inflammatory response following cell lysis. Remarkably, under the acidic microenvironment, the controlled release of H2 exhibits precise synergistic antioxidant and anti‐inflammatory effects with MNPs. Moreover, the ICG, the second near‐infrared dye currently approved for clinical use, possesses excellent NIR‐II FL imaging properties that facilitate the diagnosis of deep tissue diseases and provide the right time‐point for PTT.

Abstract A supercapacitor‐based coordinated synthetic inertia (SCSI) scheme for a voltage source converter‐based HVDC (VSC‐HVDC)‐integrated offshore wind farm (OWF) is proposed. The proposed SCSI allows the OWF to provide a designated inertial response to an onshore grid. Under the SCSI scheme, a supercapacitor is added to the DC side of each wind turbine generator via a bidirectional DC/DC converter, varying its voltage along with the offshore frequency to synthesise the desired inertial response. The HVDC grid side VSC employs a DC voltage/frequency droop control to convey the onshore frequency information to DC voltage without communication. Meanwhile, the wind farm side VSC regulates the offshore frequency to couple with the conveyed onshore frequency, considering voltage drop across the DC cables. An offshore frequency switching algorithm is incorporated to avoid undesired SCSI maloperation under offshore faults. The key parameters of the proposed SCSI are optimised through a small signal stability analysis. The effectiveness of the SCSI scheme is evaluated using a modified IEEE 39‐bus test system. The results show that the proposed SCSI scheme can provide required inertial support from WTG‐installed supercapacitors to the onshore grid through the VSC‐HVDC link, significantly improving the onshore frequency stability.

Solar generation systems with battery energy storage have become a research hotspot in recent years. This paper proposes a grid-forming control for such a system. The inverter control consists of the inner dq-axis current control, the dq-axis voltage control, the phase-locked loop (PLL) based frequency control, and the DC voltage control. The proposed control embeds the PLL into the grid-forming inverter control, offering the advantages of better synchronization and fault current-limiting capability. With the proposed control, the battery energy storage is able to provide inertial and primary frequency support during the grid frequency disturbance. Simulation models are established in PSCAD/EMTDC, and the results during the active power variation and AC voltage variation, the grid frequency disturbance, grid fault, and mode switch validate the effectiveness of the proposed control.

Abstract System kinetic inertia is declining due to the rapid replacement of synchronous generators (SG) by renewable power generations (RPG). To maintain grid inertia, this paper proposes a generic synthetic inertia (GSI) scheme for RPGs, enabling inertial response by a supercapacitor (SC) bank integrated with a voltage source inverter (VSI) DC link via a DC/DC converter. A GSI control loop is developed for the DC/DC converter controller to vary the SC voltage along with the grid frequency for power exchange following the SG swing equation. The GSI scheme realizes plug‐and‐play advantage without modifying the RPG original system. Small‐signal stability analysis is carried out to optimize the GSI controller parameters. The performance of the GSI scheme is evaluated using a modified IEEE 39‐bus test system.

Abstract Increasing penetration level of renewable energy results in unprecedented operational challenges of AC grids due to generation uncertainty and reduced inertia. In grid emergencies, Fast active Power output Reduction (FPR) is demanded to drop wind turbine generator (WTG) power outputs faster than usual. However, the power mismatch between WTG mechanical power input and reduced electrical power output resulted from FPR can lead to rotor overspeed, which cannot be timely nullified by slow‐responding pitch control. Therefore, this paper proposes a novel FPR scheme for doubly‐fed induction generator (DFIG)‐based WTG through coordinated control of DC chopper and pitch angle. Specifically, the FPR command is executed by DFIG rotor‐side converter control, while rotor overspeed is restricted by triggering the DC chopper to dissipate the mismatched power. The pitch angle is actuated at a maximal rate to eliminate the mismatched power and switch off the DC chopper. The effectiveness of the proposed FPR scheme is verified through comparative simulation studies under FPR command execution and a grid fault. It shows the proposed scheme can achieve FPR in tens of milliseconds, avoid rotor overspeed and provide low‐voltage ride‐through capability in a fully‐controlled manner.

The diode rectifier unit (DRU)-based high-voltage DC (DRU-HVDC) system is a promising solution for offshore wind energy transmission thanks to its compact design, high efficiency, and strong reliability. Herein we investigate the feasibility of the DRU-HVDC system considering onshore and offshore AC grid faults, DC cable faults, and internal DRU faults. To ensure safe operation during the faults, the wind turbine (WT) converters are designed to operate in either current-limiting or voltage-limiting mode to limit potential excessive overcurrent or overvoltage. Strategies for providing fault currents using WT converters during offshore AC faults to enable offshore overcurrent and differential fault protection are investigated. The DRU-HVDC system is robust against various faults, and it can automatically restore power transmission after fault isolation. Simulation results confirm the system performance under various fault conditions. Keywords: Diode rectifier unit (DRU), Fault protection, HVDC transmission, Offshore wind farm

This paper investigates the integration of large offshore wind farms using parallel HVAC and diode-rectifier based HVDC (DR-HVDC) systems. Three different operation modes, i.e. HVAC operation mode, DR-HVDC operation mode and parallel operation mode are investigated. A wind turbine control scheme including distributed control and centralised control is proposed to ensure the stable operation of the offshore wind farms under different operation modes. The proposed control requires no switching of the distributed control strategy when the operation mode is changed. Moreover, power flow between the DR-HVDC link and HVAC link under parallel operation can be well controlled with the centralised control. Simulation results in PSCAD/EMTDC verify the proposed control during transition among the three operation modes.

Experimental and numerical experiments were carried out to study the coffee rings or coffee splats formed by droplet evaporation with micro or nano polystyrene sphere particles (Dp = 10 μm or 100 nm). Particle image velocimetry (PIV) and a high-resolution camera were used in this experiment, along with a temperature-controlled heater and a data-acquisition computer. The results showed that a nano particle could form a homogeneous coffee splat, instead of the common coffee ring formed when using micro particles. In order to account for this phenomenon, this paper developed a complex multiphase model, one which included the smooth particle hydrodynamics (SPH) fluid model coupled with the van der Waals equation of state for droplet evaporation, the rigid particle model of finite-size micro particles, and the point–particle model of the nanometer particles. The numerical simulation was operated on a GPU-based algorithm and tested by four validation cases. A GPU could calculate 533 times the speed of a single-core CPU for about 300,000 particles. The results showed that, for rigid solid particles, the forms emerged spontaneously on the wall, and their structure was mainly affected by the boundary wettability, and less affected by the fluid flow and thermal condition. When the wall temperature was low, it was easier for the particles to be deposited on the contact line. At high wall temperature, the coffee ring effect would be weakened, and the particles were more likely to be deposited in the droplet center. The hydrophilic surface produced a larger coffee ring compared to the hydrophobic surface. The experimental and numerical results proved that particle size could play a significant role during the particle deposition, which may be a possible route for producing uniform-distributed and nano-structure coatings.

Abstract Triple-negative breast cancer (TNBC) is a subtype of breast cancer in which the estrogen receptor and progesterone receptor are not expressed, and human epidermal growth factor receptor 2 is not amplified or overexpressed either, which make the clinical diagnosis and treatment very challenging. Molecular imaging can provide an effective way to diagnose TNBC. Upconversion nanoparticles (UCNPs), are a promising new generation of molecular imaging probes. However, UCNPs still need to be improved for tumor-targeting ability and biocompatibility. This study describes a novel probe based on cancer cell membrane-coated upconversion nanoparticles (CCm-UCNPs), owing to the low immunogenicity and homologous-targeting ability of cancer cell membranes, and modified multifunctional UCNPs. This probe exhibits excellent performance in breast cancer molecular classification and TNBC diagnosis through UCL/MRI/PET tri-modality imaging in vivo. By using this probe, MDA-MB-231 was successfully differentiated between MCF-7 tumor models in vivo. Based on the tumor imaging and molecular classification results, the probe is also expected to be modified for drug delivery in the future, contributing to the treatment of TNBC. The combination of nanoparticles with biomimetic cell membranes has the potential for multiple clinical applications.

Abstract Purpose There has been no satisfactory treatment for advanced melanoma until now. Targeted radionuclide therapy (TRNT) may be a promising option for this heretofore lethal disease. Our goal in this study was to synthesize 131I-N-(2-(diethylamino)ethyl)-5-(iodo-131I)picolinamide (131I-5-IPN) and evaluate its therapeutic ability and toxicity as a radioiodinated melanin-targeting therapeutic agent. Methods The trimethylstannyl precursor was synthesized and labeled with 131I to obtain 131I-5-IPN. The pharmacokinetics of 131I-5-IPN was evaluated through SPECT imaging, and its biodistribution was assessed in B16F10 tumor models and in A375 human-to-mouse xenografts. For TRNT, B16F10 melanoma-bearing mice were randomly allocated to receive one of five treatments (n = 10 per group): group A (the control group) received 0.1 mL saline; group B was treated with an equimolar dose of unlabeled precursor; group C received 18.5 MBq of [131I]NaI; group D and E received one or two dose of 18.5 MBq 131I-5-IPN, respectively. TRNT efficacy was evaluated through tumor volume measurement and biology study. The toxic effects of 131I-5-IPN on vital organs were assessed with laboratory tests and histopathological examination. The radiation absorbed dose to vital organs was estimated based on biodistribution data. Results 131I-5-IPN was successfully prepared with a good radiochemistry yield (55% ± 5%, n = 5), and it exhibited a high uptake ratio in melanin-positive B16F10 cells which indicating high specificity. SPECT imaging and biodistribution of 131I-5-IPN showed lasting high tumor uptake in pigmented B16F10 models for 72 h. TRNT with 131I-5-IPN led to a significant anti-tumor effect and Groups D and E displayed an extended median survival compared to groups A, B, and C. The highest absorbed dose to a vital organ was 0.25 mSv/MBq to the liver; no obvious injury to the liver or kidneys was observed during treatment. 131I-5-IPN treatment was associated with reduction of expression of proliferating cell nuclear antigen (PCNA) and Ki67 and cell cycle blockage in G2/M phase in tumor tissues. Decreased vascular endothelial growth factor and CD31 expression, implying reduced tumor growth, was noted after TRNT. Conclusion We successfully synthesized 131I-5-IPN, which presents long-time retention in melanotic melanoma. TRNT with 131I-5-IPN has the potential to be a safe and effective strategy for management of pigmented melanoma.

Abstract In the publication of this article [1], there is an error in affiliation 1. The revised affiliation has now been included in this correction.