基于模块化多电平换流器MMC(modular multilevel converter)的高压直流输电HVDC(high voltage direct current transmission)因具有无源网络支撑等优势而被广泛应用于大容量新能源外送消纳。受电力电子设备交互作用等因素影响,送端系统...基于模块化多电平换流器MMC(modular multilevel converter)的高压直流输电HVDC(high voltage direct current transmission)因具有无源网络支撑等优势而被广泛应用于大容量新能源外送消纳。受电力电子设备交互作用等因素影响,送端系统易发生振荡失稳现象。首先,建立了直驱风电场经MMC-HVDC并网送端系统的小扰动线性化模型,分析了风场有功输出对系统稳定性的影响。然后,建立了MMC及风机并网变流器交流侧dq阻抗模型,从阻抗角度揭示了送端系统振荡失稳机理。进一步,提出了基于MMC交流电压控制外环q轴附加阻尼的振荡抑制策略,可满足系统满功率范围内的运行稳定性要求。最后,基于全比例模型的仿真结果验证了所提振荡抑制策略的有效性。展开更多
Background Bipolar disorder is identified as a cause of severe damage to the physical,psychological and social functioning of adolescents and young adults.Aims The aim of this study is to ascertain the trends in the b...Background Bipolar disorder is identified as a cause of severe damage to the physical,psychological and social functioning of adolescents and young adults.Aims The aim of this study is to ascertain the trends in the burden of bipolar disorder among individuals aged 10-24 years at global,regional and national levels from 1990 to 2019.Methods The data analysed in this study were from the Global Burden of Diseases 2019.The numbers,rates per 100000 population,average annual percentage changes(AAPCs)of incidence,prevalence and years lived with disability(YLDs)of bipolar disorder are reported at the global,regional and national levels among individuals aged 10-24 years.Global trends by age,sex and Social Development Index(SDI)were further analysed.Results Globally,the incidence of bipolar disorder among adolescents and young adults increased from 79.21 per 100000 population(95%uncertainty interval(Ul):58.13 to 105.15)in 1990 to 84.97 per 100000 population(95%Ul:61.73 to 113.46)in 2019,AAPC 0.24(95%confidence interval(Cl):0.22 to 0.26).In the past three decades,there has been an increase in incidence,prevalence and YLDs in both males and females.The largest increase in incidence between 1990 and 2019 was observed in those aged 20-24 years old from 51.76 per 100000 population(95%Ul:26.81 to 87.20)in 1990 to 58.37 per 100000 population(95%UI:30.39 to 98.55)in 2019;AAPC 0.42(95%Cl:0.38 to 0.47).By the SDI quintile,the largest increase in incidence was observed in the middle SDl;however,the high SDI countries had the highest incidence.Regionally,the largest increase in incidence was observed in southern Latin America.At the national level,the most pronounced increase in the incidence was in Greenland.Conclusions The global increase in incidence among adolescents and young adults between 1990 and 2019 indicates that strategies to improve their mental health still need to be emphasised.展开更多
Ferroelectric materials are promising candidates for ultraviolet photodetectors due to their ferroelectric effect.In this work,a BaTiO_(3)/p-GaN/Au hybrid heterojunction-Schottky self-driven ultraviolet photodetector ...Ferroelectric materials are promising candidates for ultraviolet photodetectors due to their ferroelectric effect.In this work,a BaTiO_(3)/p-GaN/Au hybrid heterojunction-Schottky self-driven ultraviolet photodetector was fabricated with excellent bipolar photoresponse property.At 0 V bias,the direction of the photocurrent can be switched by flipping the depolarization field of BaTiO_(3),which allows the performance of photodetectors to be controlled by the ferroelectric effect.Meanwhile,a relatively large responsivity and a fast response speed can be also observed.In particular,when the depolarization field of BaTiO_(3) is in the same direction of the built-in electric field of the Au/p-GaN Schottky junction(up polarized state),the photodetector exhibits a high responsivity of 18 mA/W at 360 nm,and a fast response speed of<40 ms at 0 V.These findings pave a new way for the preparation of high-performance photodetectors with bipolar photocurrents.展开更多
Background Understanding the evolution of circadian rhythm dysfunction and psychopathology in the high-risk population has important implications for the prevention of bipolar disorder.Nevertheless,some of the previou...Background Understanding the evolution of circadian rhythm dysfunction and psychopathology in the high-risk population has important implications for the prevention of bipolar disorder.Nevertheless,some of the previous studies on the emergence of psychopathologies and circadian dysfunction among high-risk populations were inconsistent and limited.Aims To examine the prevalence rates of sleep and circadian dysfunctions,mental disorders and their symptoms in the offspring of parents with(O-BD)and without bipolar disorder(O-control).Methods The study included 191 O-BD and 202 O-control subjects aged 6-21 years from the Greater Bay Area,China.The diagnoses and symptoms of sleep/circadian rhythm and mental disorders were assessed by the Diagnostic Interview for Sleep Patterns and Disorders,and the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version,respectively.Generalised estimating equations and shared frailty proportional hazards models of survival analysis were applied to compare the outcomes in the offspring.Results Adjusting for age,sex and region of recruitment,there was a significantly higher risk of delayed sleep phase symptoms(9.55%vs 2.58%,adjusted OR:4.04)in O-BD than in O-control.O-BD had a nearly fivefold higher risk of mood disorders(11.70%vs 3.47%,adjusted OR:4.68)and social anxiety(6.28%vs 1.49%,adjusted OR:4.70),a fourfold higher risk of depressive disorders(11.17%vs 3.47%,adjusted OR:3.99)and a threefold higher risk of mood symptoms(20.74%vs 10.40%,adjusted OR:2.59)than O-control.Subgroup analysis revealed that O-BD children(aged under 12 years)had a nearly 2-fold higher risk of any mental and behavioural symptoms than O-control,while there was a nearly 4-fold higher risk of delayed sleep phase symptoms,a 7.5-fold higher risk of social anxiety and a 3-fold higher risk of mood symptoms in O-BD adolescents(aged 12 years and over).Conclusions There was an increase in delayed sleep phase symptoms in O-BD adolescents compared with their control counterparts,confirming the central role of circadian rhythm dysfunction in bipolar disorder.The findings of the specific age-related and stage-related developmental patterns of psychopathologies and circadian dysfunction in children and adolescent offspring of parents with bipolar disorder paved the way to develop specific and early clinical intervention and prevention strategies.展开更多
Bipolar disorder is characterised by recurrent and alternating episodes of mania/hypomania and depression.Current breakthroughs in functional MRI techniques have uncovered the functional neuroanatomy of bipolar disord...Bipolar disorder is characterised by recurrent and alternating episodes of mania/hypomania and depression.Current breakthroughs in functional MRI techniques have uncovered the functional neuroanatomy of bipolar disorder.However,the pathophysiology underlying mood instability,mood switching and the development of extreme mood states is less well understood.This reviewpresents a comprehensive overviewof current evidence from functional MRI studies from the perspective of mood states.We first summarise the disrupted brain activation patterns and functional connectivity that have been reported in bipolar disorder,irrespective of the mood state.We next focus on research that solely included patients in a single mood state for a better understanding of the pathophysiology of bipolar disorder and research comparing patients with different mood states to dissect mood state-related effects.Finally,we briefly summarise current theoretical models and conclude this review by proposing potential avenues for future research.A comprehensive understanding of the pathophysiology with consideration of mood states could not only deepen our understanding of how acute mood episodes develop at a neurophysiological level but could also facilitate the identification of biological targets for personalised treatment and the development of new interventions for bipolar disorder.展开更多
BACKGROUND Recently,a growing number of adolescents have been afflicted with mental disorders,with annual morbidity rates on the rise.This trend has been exacerbated by the global coronavirus disease 2019(COVID-19)pan...BACKGROUND Recently,a growing number of adolescents have been afflicted with mental disorders,with annual morbidity rates on the rise.This trend has been exacerbated by the global coronavirus disease 2019(COVID-19)pandemic,leading to a surge in suicide and self-harm rates among this demographic.AIM To investigate the impact of the COVID-19 pandemic on adolescent bipolar disorder(BD),along with the underlying factors contributing to heightened rates of suicide and self-harm among adolescents.METHODS A comprehensive statistical analysis was conducted utilizing clinical interviews and self-reports obtained from patients or their guardians.Diagnostic criteria for BDs were based on the Diagnostic and statistical manual of mental disorders,international classification of diseases-11,and the National institute of mental health research domain criteria.Statistical analyses were performed using SPSS 26.0 software,with significance set at P<0.05.RESULTS A cohort of 171 adolescents diagnosed with BD between January 1,2018,and December 31,2022,was included in the analysis.The gender distribution was 2.8:1(female to male),with ages ranging from 11 to 18 years old.Major factors contributing to adolescent BDs included familial influences,academic stress,genetic predisposition and exposure to school-related violence.Notably,a significant increase in suicide attempts and self-harm incidents was observed among adolescents with BD during the COVID-19 pandemic.Statistical analysis indicated that the pandemic exacerbated familial discord and heightened academic stress,thereby amplifying the prevalence of suicidal behavior and self-harm among adolescents.CONCLUSION The COVID-19 pandemic has exacerbated familial tensions and intensified the incidence of suicide and self-harm among adolescents diagnosed with BD.This study underscores the urgent need for societal,familial and educational support systems to prioritize the well-being of adolescents and offers valuable insights and guidelines for the prevention,diagnosis and treatment of adolescent BDs.展开更多
The concepts of connectedness play a critical role in digital picture segmentation and analyses. However, the crisp nature of set theory imposes hard boundaries that restrict the extension of the underlying topologica...The concepts of connectedness play a critical role in digital picture segmentation and analyses. However, the crisp nature of set theory imposes hard boundaries that restrict the extension of the underlying topological notions and results. Whilst fuzzy set theory was introduced to address this inherent drawback, most human processes are not just fuzzy but also double-sided. Most phenomena will exhibit both a positive side and a negative side. Therefore, it is not enough to have a theory that addresses imprecision, uncertainty and ambiguity;rather, the theory must also be able to model polarity. Hence the study of bipolar fuzzy theory is of potential significance in an attempt to model real-life phenomena. This paper extends some concepts of fuzzy digital topology to bipolar fuzzy subsets including some important basic properties such as connectedness and surroundedness.展开更多
The bipolar ionic liquid thruster employs ionic liquid as a propellant to discharge positively and negatively charged high-energy particles under an alternating current(AC)power source,effectively suppressing electroc...The bipolar ionic liquid thruster employs ionic liquid as a propellant to discharge positively and negatively charged high-energy particles under an alternating current(AC)power source,effectively suppressing electrochemical reaction and ensuring charge neutrality.Determining an optimal AC supply power source frequency is critical for sustained stable thruster operation.This study focuses on the emission characteristics of the ionic liquid thruster under varied AC conditions.The AC power supply was set within the frequency range of 0.5-64 Hz,with eight specific frequency conditions selected for experimentation.The experimental results indicate that the thruster operates steadily within a voltage range of±1470 to±1920 V,with corresponding positive polarity current ranging from 0.41 to 4.91μA and negative polarity current ranging from−0.49 to−4.10μA.During voltage polarity switching,an emission delay occurs,manifested as a prominent peak signal caused by circuit capacitance characteristics and a minor peak signal resulting from liquid droplets.Extended emission test was conducted at 16 Hz,demonstrating approximately 1 h and 50 min of consistent emission before intermittent discharge.These findings underscore the favorable impact of AC conditions within the 8-16 Hz range on the self-neutralization capability of the ionic liquid thruster.展开更多
Bipolar membranes(BPMs)exhibit the unique capability to regulate the operating environment of electrochemical system through the water dissociation-combination processes.However,the industrial utilization of BPMs is l...Bipolar membranes(BPMs)exhibit the unique capability to regulate the operating environment of electrochemical system through the water dissociation-combination processes.However,the industrial utilization of BPMs is limited by instability and serious energy consumption.The current-induced membrane discharge(CIMD)at high-current conditions has a negative influence on the performance of anion-exchange membranes,but the underlying ion transport mechanisms in the BPMs remain unclear.Here,the CIMD-coupled Poisson-Nernst-Planck(PNP)equations are used to explore the ion transport mechanisms in the BPMs for both reverse bias and forward bias at neutral and acid-base conditions.It is demonstrated that the CIMD effect in the reverse-bias mode can be suppressed by enhancing the diffusive transport of salt counter-ions(Na^(+)and Cl^(−))into the BPMs,and that in the forward-bias mode with acid-base electrolytes can be suppressed by matching the transport rate of water counter-ions(H_(3)O^(+)and OH^(−)).Suppressing the CIMD can promote the water dissociation in the reverse-bias mode,as well as overcome the plateau of limiting current density and reduce the interfacial blockage of salt co-ions(Cl^(−))in the anion-exchange layer in the forward-bias mode with acid-base electrolytes.Our work highlights the importance of regulating ion crossover transport on improving the performance of BPMs.展开更多
In the realm of proton exchange membrane fuel cells(PEMFCs),the bipolar plates(BPs)are indispensable and serve pivotal roles in distributing reactant gases,collecting current,facilitating product water removal,and coo...In the realm of proton exchange membrane fuel cells(PEMFCs),the bipolar plates(BPs)are indispensable and serve pivotal roles in distributing reactant gases,collecting current,facilitating product water removal,and cooling the stack.Metal BPs,characterized by outstanding manufacturability,cost-effectiveness,higher power density,and mechanical strength,are emerging as viable alternatives to traditional graphite BPs.The foremost challenge for metal BPs lies in enhancing their corrosion resistance and conductivity under acidic conditions,necessitating the application of various coatings on their surfaces to ensure superior performance.This review summarizes and compares recent advancements in the research of eight distinct types of coatings for BPs in PEMFCs,including noble metal,carbide,ni-tride,and amorphous carbon(a-C)/metal compound composite coatings.The various challenges encountered in the manufacturing and fu-ture application of these coatings are also delineated.展开更多
Food Waste(FW)is a pressing environmental concern that affects every country globally.About one-third of the food that is produced ends up as waste,contributing to the carbon footprint.Hence,the FW must be properly tr...Food Waste(FW)is a pressing environmental concern that affects every country globally.About one-third of the food that is produced ends up as waste,contributing to the carbon footprint.Hence,the FW must be properly treated to reduce environmental pollution.This study evaluates a few available Food Waste Treatment(FWT)technologies,such as anaerobic digestion,composting,landfill,and incineration,which are widely used.A Bipolar Picture Fuzzy Set(BPFS)is proposed to deal with the ambiguity and uncertainty that arise when converting a real-world problem to a mathematical model.A novel Criteria Importance Through Intercriteria Correlation-Stable Preference Ordering Towards Ideal Solution(CRITIC-SPOTIS)approach is developed to objectively analyze FWT selection based on thirteen criteria covering the industry’s technical,environmental,and entrepreneurial aspects.The CRITIC method is used for the objective analysis of the importance of each criterion in FWT selection.The SPOTIS method is adopted to rank the alternative hassle-free,following the criteria.The proposed model offers a rank reversal-free model,i.e.,the rank of the alternatives remains unaffected even after the addition or removal of an alternative.In addition,comparative and sensitivity analyses are performed to ensure the reliability and robustness of the proposed model and to validate the proposed result.展开更多
BACKGROUND Hip fractures account for 23.8%of all fractures in patients over the age of 75 years.More than half of these patients are older than 80 years.Bipolar hemiarthroplasty(BHA)was established as an effective man...BACKGROUND Hip fractures account for 23.8%of all fractures in patients over the age of 75 years.More than half of these patients are older than 80 years.Bipolar hemiarthroplasty(BHA)was established as an effective management option for these patients.Various approaches can be used for the BHA procedure.However,there is a high risk of postoperative dislocation.The conjoined tendon-preserving posterior(CPP)lateral approach was introduced to reduce postoperative dislocation rates.AIM To evaluate the effectiveness and safety of the CPP lateral approach for BHA in elderly patients.METHODS We retrospectively analyzed medical data from 80 patients with displaced femoral neck fractures who underwent BHA.The patients were followed up for at least 1 year.Among the 80 patients,57(71.3%)were female.The time to operation averaged 2.3 d(range:1-5 d).The mean age was 80.5 years(range:67-90 years),and the mean body mass index was 24.9 kg/m^(2)(range:17-36 kg/m^(2)).According to the Garden classification,42.5%of patients were typeⅢand 57.5%of patients were typeⅣ.Uncemented bipolar hip prostheses were used for all patients.Torn conjoined tendons,dislocations,and adverse complications during and after surgery were recorded.RESULTS The mean postoperative follow-up time was 15.3 months(range:12-18 months).The average surgery time was 52 min(range:40-70 min)with an average blood loss of 120 mL(range:80-320 mL).The transfusion rate was 10%(8 of 80 patients).The gemellus inferior was torn in 4 patients(5%),while it was difficult to identify in 2 patients(2.5%)during surgery.The posterior capsule was punctured by the fractured femoral neck in 3 patients,but the conjoined tendon and the piriformis tendon remained intact.No patients had stem varus greater than 3 degrees or femoral fracture.There were no patients with stem subsidence more than 5 mm at the last follow-up.No postoperative dislocations were observed throughout the follow-up period.No significance was found between preoperative and postoperative mean Health Service System scores(87.30±2.98 vs 86.10±6.10,t=1.89,P=0.063).CONCLUSION The CPP lateral approach can effectively reduce the incidence of postoperative dislocation without increasing perioperative complications.For surgeons familiar with the posterior lateral approach,there is no need for additional surgical instruments,and it does not increase surgical difficulty.展开更多
Bipolar disorder presents significant challenges in clinical management, characterized by recurrent episodes of depression and mania often accompanied by impairment in functioning. This study investigates the efficacy...Bipolar disorder presents significant challenges in clinical management, characterized by recurrent episodes of depression and mania often accompanied by impairment in functioning. This study investigates the efficacy of pharmacological interventions and rehabilitation strategies to improve patient outcomes and quality of life. Utilizing a randomized controlled trial with multiple treatment arms, participants will receive pharmacotherapy, polypharmacotherapy, rehabilitation interventions, or combination treatments. Outcome measures will be assessed using standardized scales, including the Hamilton Depression Scale, Yale-Brown Obsessive Compulsive Scale (Y-BOCS), and Mania Scale. Preliminary data suggest improvements in symptom severity and functional outcomes with combination treatments. This research aims to inform clinical practice, guide treatment decisions, and ultimately enhance the quality of care for individuals living with bipolar disorder. Findings will be disseminated through peer-reviewed journals and scientific conferences to advance knowledge in this field.展开更多
BACKGROUND Bipolar disorder(BD)is a severe mental illness.BD often coexists with borderline personality disorders,making the condition more complex.AIM To explore the differences in cognitive impairment between patien...BACKGROUND Bipolar disorder(BD)is a severe mental illness.BD often coexists with borderline personality disorders,making the condition more complex.AIM To explore the differences in cognitive impairment between patients with BD and those with BD comorbid with borderline personality disorder.METHODS Eighty patients with BD and comorbid borderline personality disorder and 80 patients with BD alone were included in groups A and B,respectively,and 80 healthy volunteers were included as controls.Cognitive function in each group was evaluated using the Chinese version of the repeatable battery for the assess-ment of neuropsychological status(RBANS),the Stroop color-word test,and the Wechsler intelligence scale-revised(WAIS-RC).RESULTS The indices of the RBANS,Stroop color-word test,and WAIS-RC in groups A and B were significantly lower than those of the control group(P<0.05).Group A had significantly longer Stroop color-word test times for single-character,single-color,double-character,and double-color,lower scores of immediate memory,visual breadth,verbal function dimensions and total score of the RBANS,as well as lower scores of verbal IQ,performance IQ,and overall IQ of the WAIS-RC compared with group B(P<0.05).Compared to group B,group A exhibited significantly longer single-character time,single-color time,double-character time,and double-color time in the Stroop color-word test(P<0.05).CONCLUSION The cognitive function of patients with BD complicated with borderline personality disorder is lower than that of patients with BD.展开更多
Bipolar disorder is a serious mental condition that may be caused by any kind of stress or emotional upset experienced by the patient.It affects a large percentage of people globally,who fluctuate between depression a...Bipolar disorder is a serious mental condition that may be caused by any kind of stress or emotional upset experienced by the patient.It affects a large percentage of people globally,who fluctuate between depression and mania,or vice versa.A pleasant or unpleasant mood is more than a reflection of a state of mind.Normally,it is a difficult task to analyze through physical examination due to a large patient-psychiatrist ratio,so automated procedures are the best options to diagnose and verify the severity of bipolar.In this research work,facial microexpressions have been used for bipolar detection using the proposed Convolutional Neural Network(CNN)-based model.Facial Action Coding System(FACS)is used to extract micro-expressions called Action Units(AUs)connected with sad,happy,and angry emotions.Experiments have been conducted on a dataset collected from Bahawal Victoria Hospital,Bahawalpur,Pakistan,Using the Patient Health Questionnaire-15(PHQ-15)to infer a patient’s mental state.The experimental results showed a validation accuracy of 98.99%for the proposed CNN modelwhile classification through extracted featuresUsing SupportVectorMachines(SVM),K-NearestNeighbour(KNN),and Decision Tree(DT)obtained 99.9%,98.7%,and 98.9%accuracy,respectively.Overall,the outcomes demonstrated the stated method’s superiority over the current best practices.展开更多
Abnormal expression of microRNAs is connected to brain development and disease and could provide novel biomarkers for the diagnosis and prognosis of bipolar disorder. We performed a PubMed search for microRNA biomarke...Abnormal expression of microRNAs is connected to brain development and disease and could provide novel biomarkers for the diagnosis and prognosis of bipolar disorder. We performed a PubMed search for microRNA biomarkers in bipolar disorder and found 18 original research articles on studies performed with human patients and published from January 2011 to June 2023. These studies included microRNA profiling in bloodand brain-based materials. From the studies that had validated the preliminary findings,potential candidate biomarkers for bipolar disorder in adults could be miR-140-3p,-30d-5p,-330-5p,-378a-5p,-21-3p,-330-3p,-345-5p in whole blood, miR-19b-3p,-1180-3p,-125a-5p, let-7e-5p in blood plasma, and miR-7-5p,-23b-5p,-142-3p,-221-5p,-370-3p in the blood serum. Two of the studies had investigated the changes in microRNA expression of patients with bipolar disorder receiving treatment. One showed a significant increase in plasma miR-134 compared to baseline after 4 weeks of treatment which included typical antipsychotics, atypical antipsychotics, and benzodiazepines. The other study had assessed the effects of prescribed medications which included neurotransmitter receptorsite binders(drug class B) and sedatives, hypnotics, anticonvulsants, and analgesics(drug class C) on microRNA results. The combined effects of the two drug classes increased the significance of the results for miR-219 and-29c with miR-30e-3p and-526b* acquiring significance. MicroRNAs were tested to see if they could serve as biomarkers of bipolar disorder at different clinical states of mania, depression, and euthymia. One study showed that upregulation in whole blood of miR-9-5p,-29a-3p,-106a-5p,-106b-5p,-107,-125a-3p,-125b-5p and of miR-107,-125a-3p occurred in manic and euthymic patients compared to controls, respectively, and that upregulation of miR-106a-5p,-107 was found for manic compared to euthymic patients. In two other studies using blood plasma,downregulation of miR-134 was observed in manic patients compared to controls, and dysregulation of miR-134,-152,-607,-633,-652,-155 occurred in euthymic patients compared to controls. Finally, microRNAs such as miR-34a,-34b,-34c,-137, and-140-3p,-21-3p,-30d-5p,-330-5p,-378a-5p,-134,-19b-3p were shown to have diagnostic potential in distinguishing bipolar disorder patients from schizophrenia or major depressive disorder patients, respectively. Further studies are warranted with adolescents and young adults having bipolar disorder and consideration should be given to using animal models of the disorder to investigate the effects of suppressing or overexpressing specific microRNAs.展开更多
基于模块化多电平换流器的高压柔性直流输电系统(modular multilevel converter-based high voltage direct current,MMC-HVDC)常采用双极接线方式以提高系统功率输送能力和可靠性。然而目前对于风电场经柔直外送系统的稳定性研究集中...基于模块化多电平换流器的高压柔性直流输电系统(modular multilevel converter-based high voltage direct current,MMC-HVDC)常采用双极接线方式以提高系统功率输送能力和可靠性。然而目前对于风电场经柔直外送系统的稳定性研究集中于单极接线方式,孤岛直驱风电场与采用不同双极协调控制的双极MMC-HVDC互联系统小信号稳定性问题还有待进一步探究。该文首先考虑频率耦合特性、参考系初相位和直流侧耦合特性的影响,分别建立了采用双U/f下垂控制和定U/f-P/Q控制的双极MMC-HVDC系统交流侧等效SISO阻抗模型,并详细分析了金属回线阻抗和双极间功率均分度对交流阻抗特性的影响。接着对比研究了两种协调控制中共有控制环路和特有控制环路对交流侧负电阻特性及互联系统稳定性的影响规律。最后,孤岛直驱风电场经两种双极协调控制下双极MMC-HVDC外送系统Matlab/Simulink时域仿真结果和硬件在环半实物实时仿真实验结果验证了所提出的小信号阻抗模型的精确性和稳定性分析结论的有效性。展开更多
直流线路单极接地短路故障是基于模块化多电平换流器的高压直流输电(modular multilevel converter based high voltage direct current,MMC-HVDC)系统中最常见的故障类型,分析其故障特性、掌握故障电流水平对于继电保护的设计及相关参...直流线路单极接地短路故障是基于模块化多电平换流器的高压直流输电(modular multilevel converter based high voltage direct current,MMC-HVDC)系统中最常见的故障类型,分析其故障特性、掌握故障电流水平对于继电保护的设计及相关参数的优化具有重要意义。作为分析基础,首先分析并得出MMC直流侧故障电流表达式,然后重点针对金属回线单侧接地方式的MMC-HVDC系统,分析了直流线路故障后的故障点两侧系统在接地电阻上的耦合作用,根据耦合作用的产生原因及本质提出了等效解耦方法,从而得出一种针对单极接地故障电流的实用计算方法。通过对比所提方法与PSCAD/EMTDC的电磁暂态仿真结果,验证了所提计算方法的正确性。展开更多
文摘基于模块化多电平换流器MMC(modular multilevel converter)的高压直流输电HVDC(high voltage direct current transmission)因具有无源网络支撑等优势而被广泛应用于大容量新能源外送消纳。受电力电子设备交互作用等因素影响,送端系统易发生振荡失稳现象。首先,建立了直驱风电场经MMC-HVDC并网送端系统的小扰动线性化模型,分析了风场有功输出对系统稳定性的影响。然后,建立了MMC及风机并网变流器交流侧dq阻抗模型,从阻抗角度揭示了送端系统振荡失稳机理。进一步,提出了基于MMC交流电压控制外环q轴附加阻尼的振荡抑制策略,可满足系统满功率范围内的运行稳定性要求。最后,基于全比例模型的仿真结果验证了所提振荡抑制策略的有效性。
基金the National Natural Science Foundation of China(grant number 71974114)。
文摘Background Bipolar disorder is identified as a cause of severe damage to the physical,psychological and social functioning of adolescents and young adults.Aims The aim of this study is to ascertain the trends in the burden of bipolar disorder among individuals aged 10-24 years at global,regional and national levels from 1990 to 2019.Methods The data analysed in this study were from the Global Burden of Diseases 2019.The numbers,rates per 100000 population,average annual percentage changes(AAPCs)of incidence,prevalence and years lived with disability(YLDs)of bipolar disorder are reported at the global,regional and national levels among individuals aged 10-24 years.Global trends by age,sex and Social Development Index(SDI)were further analysed.Results Globally,the incidence of bipolar disorder among adolescents and young adults increased from 79.21 per 100000 population(95%uncertainty interval(Ul):58.13 to 105.15)in 1990 to 84.97 per 100000 population(95%Ul:61.73 to 113.46)in 2019,AAPC 0.24(95%confidence interval(Cl):0.22 to 0.26).In the past three decades,there has been an increase in incidence,prevalence and YLDs in both males and females.The largest increase in incidence between 1990 and 2019 was observed in those aged 20-24 years old from 51.76 per 100000 population(95%Ul:26.81 to 87.20)in 1990 to 58.37 per 100000 population(95%UI:30.39 to 98.55)in 2019;AAPC 0.42(95%Cl:0.38 to 0.47).By the SDI quintile,the largest increase in incidence was observed in the middle SDl;however,the high SDI countries had the highest incidence.Regionally,the largest increase in incidence was observed in southern Latin America.At the national level,the most pronounced increase in the incidence was in Greenland.Conclusions The global increase in incidence among adolescents and young adults between 1990 and 2019 indicates that strategies to improve their mental health still need to be emphasised.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.62074148,61875194,11727902,12204474,12304111,and 12304112)the Youth Innovation Promotion Association,Chinese Academy of Sciences (Grant No.2020225)+1 种基金Jilin Province Science Fund (Grant Nos.20220101053JC and 20210101145JC)Jilin Province Young and Middle-Aged Science and Technology Innovation Leaders and Team Project (Grant No.20220508153RC)。
文摘Ferroelectric materials are promising candidates for ultraviolet photodetectors due to their ferroelectric effect.In this work,a BaTiO_(3)/p-GaN/Au hybrid heterojunction-Schottky self-driven ultraviolet photodetector was fabricated with excellent bipolar photoresponse property.At 0 V bias,the direction of the photocurrent can be switched by flipping the depolarization field of BaTiO_(3),which allows the performance of photodetectors to be controlled by the ferroelectric effect.Meanwhile,a relatively large responsivity and a fast response speed can be also observed.In particular,when the depolarization field of BaTiO_(3) is in the same direction of the built-in electric field of the Au/p-GaN Schottky junction(up polarized state),the photodetector exhibits a high responsivity of 18 mA/W at 360 nm,and a fast response speed of<40 ms at 0 V.These findings pave a new way for the preparation of high-performance photodetectors with bipolar photocurrents.
基金supported by the Health and Medical Research Fund of the Food and Health Bureau of Hong Kong(03140636)and the donation fund from Mr Yip WT and Mrs Yip。
文摘Background Understanding the evolution of circadian rhythm dysfunction and psychopathology in the high-risk population has important implications for the prevention of bipolar disorder.Nevertheless,some of the previous studies on the emergence of psychopathologies and circadian dysfunction among high-risk populations were inconsistent and limited.Aims To examine the prevalence rates of sleep and circadian dysfunctions,mental disorders and their symptoms in the offspring of parents with(O-BD)and without bipolar disorder(O-control).Methods The study included 191 O-BD and 202 O-control subjects aged 6-21 years from the Greater Bay Area,China.The diagnoses and symptoms of sleep/circadian rhythm and mental disorders were assessed by the Diagnostic Interview for Sleep Patterns and Disorders,and the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version,respectively.Generalised estimating equations and shared frailty proportional hazards models of survival analysis were applied to compare the outcomes in the offspring.Results Adjusting for age,sex and region of recruitment,there was a significantly higher risk of delayed sleep phase symptoms(9.55%vs 2.58%,adjusted OR:4.04)in O-BD than in O-control.O-BD had a nearly fivefold higher risk of mood disorders(11.70%vs 3.47%,adjusted OR:4.68)and social anxiety(6.28%vs 1.49%,adjusted OR:4.70),a fourfold higher risk of depressive disorders(11.17%vs 3.47%,adjusted OR:3.99)and a threefold higher risk of mood symptoms(20.74%vs 10.40%,adjusted OR:2.59)than O-control.Subgroup analysis revealed that O-BD children(aged under 12 years)had a nearly 2-fold higher risk of any mental and behavioural symptoms than O-control,while there was a nearly 4-fold higher risk of delayed sleep phase symptoms,a 7.5-fold higher risk of social anxiety and a 3-fold higher risk of mood symptoms in O-BD adolescents(aged 12 years and over).Conclusions There was an increase in delayed sleep phase symptoms in O-BD adolescents compared with their control counterparts,confirming the central role of circadian rhythm dysfunction in bipolar disorder.The findings of the specific age-related and stage-related developmental patterns of psychopathologies and circadian dysfunction in children and adolescent offspring of parents with bipolar disorder paved the way to develop specific and early clinical intervention and prevention strategies.
基金the National Key Technology R&D Program(2015BA/13B01)Beijing National Science Foundation(7222236)+1 种基金Capital Health Research and Development of Special Fund(2022-1-4111)National Natural Science Foundation of China(82071528,82171529,82271569,82371530).
文摘Bipolar disorder is characterised by recurrent and alternating episodes of mania/hypomania and depression.Current breakthroughs in functional MRI techniques have uncovered the functional neuroanatomy of bipolar disorder.However,the pathophysiology underlying mood instability,mood switching and the development of extreme mood states is less well understood.This reviewpresents a comprehensive overviewof current evidence from functional MRI studies from the perspective of mood states.We first summarise the disrupted brain activation patterns and functional connectivity that have been reported in bipolar disorder,irrespective of the mood state.We next focus on research that solely included patients in a single mood state for a better understanding of the pathophysiology of bipolar disorder and research comparing patients with different mood states to dissect mood state-related effects.Finally,we briefly summarise current theoretical models and conclude this review by proposing potential avenues for future research.A comprehensive understanding of the pathophysiology with consideration of mood states could not only deepen our understanding of how acute mood episodes develop at a neurophysiological level but could also facilitate the identification of biological targets for personalised treatment and the development of new interventions for bipolar disorder.
基金Local Special Projects in Major Health of Hubei Provincial Science and Technology Department,No.2022BCE054Key Scientific Research Projects of Hubei Polytechnic University,No.23xjz08A.
文摘BACKGROUND Recently,a growing number of adolescents have been afflicted with mental disorders,with annual morbidity rates on the rise.This trend has been exacerbated by the global coronavirus disease 2019(COVID-19)pandemic,leading to a surge in suicide and self-harm rates among this demographic.AIM To investigate the impact of the COVID-19 pandemic on adolescent bipolar disorder(BD),along with the underlying factors contributing to heightened rates of suicide and self-harm among adolescents.METHODS A comprehensive statistical analysis was conducted utilizing clinical interviews and self-reports obtained from patients or their guardians.Diagnostic criteria for BDs were based on the Diagnostic and statistical manual of mental disorders,international classification of diseases-11,and the National institute of mental health research domain criteria.Statistical analyses were performed using SPSS 26.0 software,with significance set at P<0.05.RESULTS A cohort of 171 adolescents diagnosed with BD between January 1,2018,and December 31,2022,was included in the analysis.The gender distribution was 2.8:1(female to male),with ages ranging from 11 to 18 years old.Major factors contributing to adolescent BDs included familial influences,academic stress,genetic predisposition and exposure to school-related violence.Notably,a significant increase in suicide attempts and self-harm incidents was observed among adolescents with BD during the COVID-19 pandemic.Statistical analysis indicated that the pandemic exacerbated familial discord and heightened academic stress,thereby amplifying the prevalence of suicidal behavior and self-harm among adolescents.CONCLUSION The COVID-19 pandemic has exacerbated familial tensions and intensified the incidence of suicide and self-harm among adolescents diagnosed with BD.This study underscores the urgent need for societal,familial and educational support systems to prioritize the well-being of adolescents and offers valuable insights and guidelines for the prevention,diagnosis and treatment of adolescent BDs.
文摘The concepts of connectedness play a critical role in digital picture segmentation and analyses. However, the crisp nature of set theory imposes hard boundaries that restrict the extension of the underlying topological notions and results. Whilst fuzzy set theory was introduced to address this inherent drawback, most human processes are not just fuzzy but also double-sided. Most phenomena will exhibit both a positive side and a negative side. Therefore, it is not enough to have a theory that addresses imprecision, uncertainty and ambiguity;rather, the theory must also be able to model polarity. Hence the study of bipolar fuzzy theory is of potential significance in an attempt to model real-life phenomena. This paper extends some concepts of fuzzy digital topology to bipolar fuzzy subsets including some important basic properties such as connectedness and surroundedness.
基金co-supported by the National Key R&D Program of China(No.2020YFC2201001)the Shenzhen Science and Technology Program(No.20210623091808026).
文摘The bipolar ionic liquid thruster employs ionic liquid as a propellant to discharge positively and negatively charged high-energy particles under an alternating current(AC)power source,effectively suppressing electrochemical reaction and ensuring charge neutrality.Determining an optimal AC supply power source frequency is critical for sustained stable thruster operation.This study focuses on the emission characteristics of the ionic liquid thruster under varied AC conditions.The AC power supply was set within the frequency range of 0.5-64 Hz,with eight specific frequency conditions selected for experimentation.The experimental results indicate that the thruster operates steadily within a voltage range of±1470 to±1920 V,with corresponding positive polarity current ranging from 0.41 to 4.91μA and negative polarity current ranging from−0.49 to−4.10μA.During voltage polarity switching,an emission delay occurs,manifested as a prominent peak signal caused by circuit capacitance characteristics and a minor peak signal resulting from liquid droplets.Extended emission test was conducted at 16 Hz,demonstrating approximately 1 h and 50 min of consistent emission before intermittent discharge.These findings underscore the favorable impact of AC conditions within the 8-16 Hz range on the self-neutralization capability of the ionic liquid thruster.
基金sponsored by the National Key R&D Program of China(2022YFB4602101)the Fundamental Research Funds for the Central Universities(2022ZFJH004 and 2024SMECP05)+2 种基金the National Natural Science Foundation of China(22278127 and 22378112)the Shanghai Pilot Program for Basic Research(22T01400100-18)the Postdoctoral Fellowship Program of CPSF(GZC20230801)。
文摘Bipolar membranes(BPMs)exhibit the unique capability to regulate the operating environment of electrochemical system through the water dissociation-combination processes.However,the industrial utilization of BPMs is limited by instability and serious energy consumption.The current-induced membrane discharge(CIMD)at high-current conditions has a negative influence on the performance of anion-exchange membranes,but the underlying ion transport mechanisms in the BPMs remain unclear.Here,the CIMD-coupled Poisson-Nernst-Planck(PNP)equations are used to explore the ion transport mechanisms in the BPMs for both reverse bias and forward bias at neutral and acid-base conditions.It is demonstrated that the CIMD effect in the reverse-bias mode can be suppressed by enhancing the diffusive transport of salt counter-ions(Na^(+)and Cl^(−))into the BPMs,and that in the forward-bias mode with acid-base electrolytes can be suppressed by matching the transport rate of water counter-ions(H_(3)O^(+)and OH^(−)).Suppressing the CIMD can promote the water dissociation in the reverse-bias mode,as well as overcome the plateau of limiting current density and reduce the interfacial blockage of salt co-ions(Cl^(−))in the anion-exchange layer in the forward-bias mode with acid-base electrolytes.Our work highlights the importance of regulating ion crossover transport on improving the performance of BPMs.
基金the support from the Shenzhen Science and Technology Program of China(No.JCYJ20220530161614031)National Natural Science Foundation of China(No.52471094)Shaanxi Coal Chemical Industry Technology Research Institute Co.,Ltd.
文摘In the realm of proton exchange membrane fuel cells(PEMFCs),the bipolar plates(BPs)are indispensable and serve pivotal roles in distributing reactant gases,collecting current,facilitating product water removal,and cooling the stack.Metal BPs,characterized by outstanding manufacturability,cost-effectiveness,higher power density,and mechanical strength,are emerging as viable alternatives to traditional graphite BPs.The foremost challenge for metal BPs lies in enhancing their corrosion resistance and conductivity under acidic conditions,necessitating the application of various coatings on their surfaces to ensure superior performance.This review summarizes and compares recent advancements in the research of eight distinct types of coatings for BPs in PEMFCs,including noble metal,carbide,ni-tride,and amorphous carbon(a-C)/metal compound composite coatings.The various challenges encountered in the manufacturing and fu-ture application of these coatings are also delineated.
文摘Food Waste(FW)is a pressing environmental concern that affects every country globally.About one-third of the food that is produced ends up as waste,contributing to the carbon footprint.Hence,the FW must be properly treated to reduce environmental pollution.This study evaluates a few available Food Waste Treatment(FWT)technologies,such as anaerobic digestion,composting,landfill,and incineration,which are widely used.A Bipolar Picture Fuzzy Set(BPFS)is proposed to deal with the ambiguity and uncertainty that arise when converting a real-world problem to a mathematical model.A novel Criteria Importance Through Intercriteria Correlation-Stable Preference Ordering Towards Ideal Solution(CRITIC-SPOTIS)approach is developed to objectively analyze FWT selection based on thirteen criteria covering the industry’s technical,environmental,and entrepreneurial aspects.The CRITIC method is used for the objective analysis of the importance of each criterion in FWT selection.The SPOTIS method is adopted to rank the alternative hassle-free,following the criteria.The proposed model offers a rank reversal-free model,i.e.,the rank of the alternatives remains unaffected even after the addition or removal of an alternative.In addition,comparative and sensitivity analyses are performed to ensure the reliability and robustness of the proposed model and to validate the proposed result.
文摘BACKGROUND Hip fractures account for 23.8%of all fractures in patients over the age of 75 years.More than half of these patients are older than 80 years.Bipolar hemiarthroplasty(BHA)was established as an effective management option for these patients.Various approaches can be used for the BHA procedure.However,there is a high risk of postoperative dislocation.The conjoined tendon-preserving posterior(CPP)lateral approach was introduced to reduce postoperative dislocation rates.AIM To evaluate the effectiveness and safety of the CPP lateral approach for BHA in elderly patients.METHODS We retrospectively analyzed medical data from 80 patients with displaced femoral neck fractures who underwent BHA.The patients were followed up for at least 1 year.Among the 80 patients,57(71.3%)were female.The time to operation averaged 2.3 d(range:1-5 d).The mean age was 80.5 years(range:67-90 years),and the mean body mass index was 24.9 kg/m^(2)(range:17-36 kg/m^(2)).According to the Garden classification,42.5%of patients were typeⅢand 57.5%of patients were typeⅣ.Uncemented bipolar hip prostheses were used for all patients.Torn conjoined tendons,dislocations,and adverse complications during and after surgery were recorded.RESULTS The mean postoperative follow-up time was 15.3 months(range:12-18 months).The average surgery time was 52 min(range:40-70 min)with an average blood loss of 120 mL(range:80-320 mL).The transfusion rate was 10%(8 of 80 patients).The gemellus inferior was torn in 4 patients(5%),while it was difficult to identify in 2 patients(2.5%)during surgery.The posterior capsule was punctured by the fractured femoral neck in 3 patients,but the conjoined tendon and the piriformis tendon remained intact.No patients had stem varus greater than 3 degrees or femoral fracture.There were no patients with stem subsidence more than 5 mm at the last follow-up.No postoperative dislocations were observed throughout the follow-up period.No significance was found between preoperative and postoperative mean Health Service System scores(87.30±2.98 vs 86.10±6.10,t=1.89,P=0.063).CONCLUSION The CPP lateral approach can effectively reduce the incidence of postoperative dislocation without increasing perioperative complications.For surgeons familiar with the posterior lateral approach,there is no need for additional surgical instruments,and it does not increase surgical difficulty.
文摘Bipolar disorder presents significant challenges in clinical management, characterized by recurrent episodes of depression and mania often accompanied by impairment in functioning. This study investigates the efficacy of pharmacological interventions and rehabilitation strategies to improve patient outcomes and quality of life. Utilizing a randomized controlled trial with multiple treatment arms, participants will receive pharmacotherapy, polypharmacotherapy, rehabilitation interventions, or combination treatments. Outcome measures will be assessed using standardized scales, including the Hamilton Depression Scale, Yale-Brown Obsessive Compulsive Scale (Y-BOCS), and Mania Scale. Preliminary data suggest improvements in symptom severity and functional outcomes with combination treatments. This research aims to inform clinical practice, guide treatment decisions, and ultimately enhance the quality of care for individuals living with bipolar disorder. Findings will be disseminated through peer-reviewed journals and scientific conferences to advance knowledge in this field.
基金Hebei Province Medical Science Research Project,No.20221407.
文摘BACKGROUND Bipolar disorder(BD)is a severe mental illness.BD often coexists with borderline personality disorders,making the condition more complex.AIM To explore the differences in cognitive impairment between patients with BD and those with BD comorbid with borderline personality disorder.METHODS Eighty patients with BD and comorbid borderline personality disorder and 80 patients with BD alone were included in groups A and B,respectively,and 80 healthy volunteers were included as controls.Cognitive function in each group was evaluated using the Chinese version of the repeatable battery for the assess-ment of neuropsychological status(RBANS),the Stroop color-word test,and the Wechsler intelligence scale-revised(WAIS-RC).RESULTS The indices of the RBANS,Stroop color-word test,and WAIS-RC in groups A and B were significantly lower than those of the control group(P<0.05).Group A had significantly longer Stroop color-word test times for single-character,single-color,double-character,and double-color,lower scores of immediate memory,visual breadth,verbal function dimensions and total score of the RBANS,as well as lower scores of verbal IQ,performance IQ,and overall IQ of the WAIS-RC compared with group B(P<0.05).Compared to group B,group A exhibited significantly longer single-character time,single-color time,double-character time,and double-color time in the Stroop color-word test(P<0.05).CONCLUSION The cognitive function of patients with BD complicated with borderline personality disorder is lower than that of patients with BD.
文摘Bipolar disorder is a serious mental condition that may be caused by any kind of stress or emotional upset experienced by the patient.It affects a large percentage of people globally,who fluctuate between depression and mania,or vice versa.A pleasant or unpleasant mood is more than a reflection of a state of mind.Normally,it is a difficult task to analyze through physical examination due to a large patient-psychiatrist ratio,so automated procedures are the best options to diagnose and verify the severity of bipolar.In this research work,facial microexpressions have been used for bipolar detection using the proposed Convolutional Neural Network(CNN)-based model.Facial Action Coding System(FACS)is used to extract micro-expressions called Action Units(AUs)connected with sad,happy,and angry emotions.Experiments have been conducted on a dataset collected from Bahawal Victoria Hospital,Bahawalpur,Pakistan,Using the Patient Health Questionnaire-15(PHQ-15)to infer a patient’s mental state.The experimental results showed a validation accuracy of 98.99%for the proposed CNN modelwhile classification through extracted featuresUsing SupportVectorMachines(SVM),K-NearestNeighbour(KNN),and Decision Tree(DT)obtained 99.9%,98.7%,and 98.9%accuracy,respectively.Overall,the outcomes demonstrated the stated method’s superiority over the current best practices.
文摘Abnormal expression of microRNAs is connected to brain development and disease and could provide novel biomarkers for the diagnosis and prognosis of bipolar disorder. We performed a PubMed search for microRNA biomarkers in bipolar disorder and found 18 original research articles on studies performed with human patients and published from January 2011 to June 2023. These studies included microRNA profiling in bloodand brain-based materials. From the studies that had validated the preliminary findings,potential candidate biomarkers for bipolar disorder in adults could be miR-140-3p,-30d-5p,-330-5p,-378a-5p,-21-3p,-330-3p,-345-5p in whole blood, miR-19b-3p,-1180-3p,-125a-5p, let-7e-5p in blood plasma, and miR-7-5p,-23b-5p,-142-3p,-221-5p,-370-3p in the blood serum. Two of the studies had investigated the changes in microRNA expression of patients with bipolar disorder receiving treatment. One showed a significant increase in plasma miR-134 compared to baseline after 4 weeks of treatment which included typical antipsychotics, atypical antipsychotics, and benzodiazepines. The other study had assessed the effects of prescribed medications which included neurotransmitter receptorsite binders(drug class B) and sedatives, hypnotics, anticonvulsants, and analgesics(drug class C) on microRNA results. The combined effects of the two drug classes increased the significance of the results for miR-219 and-29c with miR-30e-3p and-526b* acquiring significance. MicroRNAs were tested to see if they could serve as biomarkers of bipolar disorder at different clinical states of mania, depression, and euthymia. One study showed that upregulation in whole blood of miR-9-5p,-29a-3p,-106a-5p,-106b-5p,-107,-125a-3p,-125b-5p and of miR-107,-125a-3p occurred in manic and euthymic patients compared to controls, respectively, and that upregulation of miR-106a-5p,-107 was found for manic compared to euthymic patients. In two other studies using blood plasma,downregulation of miR-134 was observed in manic patients compared to controls, and dysregulation of miR-134,-152,-607,-633,-652,-155 occurred in euthymic patients compared to controls. Finally, microRNAs such as miR-34a,-34b,-34c,-137, and-140-3p,-21-3p,-30d-5p,-330-5p,-378a-5p,-134,-19b-3p were shown to have diagnostic potential in distinguishing bipolar disorder patients from schizophrenia or major depressive disorder patients, respectively. Further studies are warranted with adolescents and young adults having bipolar disorder and consideration should be given to using animal models of the disorder to investigate the effects of suppressing or overexpressing specific microRNAs.
文摘基于模块化多电平换流器的高压柔性直流输电系统(modular multilevel converter-based high voltage direct current,MMC-HVDC)常采用双极接线方式以提高系统功率输送能力和可靠性。然而目前对于风电场经柔直外送系统的稳定性研究集中于单极接线方式,孤岛直驱风电场与采用不同双极协调控制的双极MMC-HVDC互联系统小信号稳定性问题还有待进一步探究。该文首先考虑频率耦合特性、参考系初相位和直流侧耦合特性的影响,分别建立了采用双U/f下垂控制和定U/f-P/Q控制的双极MMC-HVDC系统交流侧等效SISO阻抗模型,并详细分析了金属回线阻抗和双极间功率均分度对交流阻抗特性的影响。接着对比研究了两种协调控制中共有控制环路和特有控制环路对交流侧负电阻特性及互联系统稳定性的影响规律。最后,孤岛直驱风电场经两种双极协调控制下双极MMC-HVDC外送系统Matlab/Simulink时域仿真结果和硬件在环半实物实时仿真实验结果验证了所提出的小信号阻抗模型的精确性和稳定性分析结论的有效性。
文摘直流线路单极接地短路故障是基于模块化多电平换流器的高压直流输电(modular multilevel converter based high voltage direct current,MMC-HVDC)系统中最常见的故障类型,分析其故障特性、掌握故障电流水平对于继电保护的设计及相关参数的优化具有重要意义。作为分析基础,首先分析并得出MMC直流侧故障电流表达式,然后重点针对金属回线单侧接地方式的MMC-HVDC系统,分析了直流线路故障后的故障点两侧系统在接地电阻上的耦合作用,根据耦合作用的产生原因及本质提出了等效解耦方法,从而得出一种针对单极接地故障电流的实用计算方法。通过对比所提方法与PSCAD/EMTDC的电磁暂态仿真结果,验证了所提计算方法的正确性。
