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Line-commutated converter based high-voltage direct-current (LCC-HVDC) has been extensively applied in power system. LCC-HVDC is prone to continuous commutation failure (CCF), which consequently causes numerous active and reactive impacts, thereby resulting in various power system security and stability issues. Given that there is no CCF predictive method at present, the effect of CCF suppression measure is still limited, and the control margin of DC commutation station and power grid cannot be fully applied, so that the negative impact of CCF is difficult to reduce through advance control. In view of this situation, this paper aims at proposing a predictive method of LCC-HVDC CCF, which occurs again during the first CF recovery process. First, the predictability of CCF is demonstrated, and the idea for predicting CCF by comparing commutation voltage is proposed; Second, the calculation equation of CCF threshold voltage is derived by analyzing the CF process; Third, a predictive method of CCF based on threshold commutation voltage is proposed; Finally, the correctness of the theoretical analysis and predictive method is verified through the CIGRE HVDC standard system. Simulation results show that the proposed method has high accuracy and can provide sufficient time margin for emergency control to suppress the LCC-HVDC CCF.

AIMS To evaluate the efficacy of sucrose in the prevention of migraine attacks. METHODS Two randomized double-blinded pilot trials were conducted, one in college students and one in adults. Migraineurs were randomized into two groups that each received an oral liquid: for students, sucrose 5 g/day (s-group; n = 12) or glucose 2.5 g/day (g-group; n = 10) for 3 months; and for adults, sucrose 5 g/day (s-group; n = 10) or fructose 2.5 g/day (f-group; n = 9) for 6 months. The primary endpoint was the frequency of migraine attacks per month, and the secondary endpoints were mean duration and severity of migraine per attack. Continuous measurements were described as mean ± standard deviation (SD). The overall significance of the effects between different groups was tested using repeated measures analysis of variance (RANOVA), and the efficacy was evaluated using an intent-to-treat analysis. RESULTS Migraine frequency in the students declined significantly in the g-group (mean reduction ± SD: 0.65 ± 0.71; P < .01), but not in the s-group (0.33 ± 2.02; P = .58). RANOVA results suggested that the secondary endpoints significantly declined over time (all P < .01) with no differences between the groups. In the adult trial, mixed-effects model analysis showed that both the primary and secondary endpoints significantly declined over time with no significant differences between the groups. CONCLUSION Long-term consumption of a 5-g dose of sucrose for adult migraineurs or a 2.5-g dose of glucose for college student migraineurs may be as effective as preventive treatments.

A regional power grid containing high-density wind power is generally connected to a load centre through long-distance transmission lines. Voltage problems, caused by wind speed fluctuation, in the sending-end grid have become increasingly serious. The variable speed wind turbine has been used to compensate the deficit in reactive power. However, the available methods could not meet the requirement because the controllable range of reactive power contributed by wind farms cannot be adjusted. A new idea of reactive power control realised by the active control before wind speed fluctuation was proposed to prevent the voltage variation. Firstly, the influence of wind speed fluctuation on voltage was analysed, and the power controllable range of wind turbines was studied. The principle and strategy of the active control of reactive power were proposed based on the model predictive control theory. Then, the active control model was established according to the system dynamic demand for reactive power. According to wind speed forecasting, the reactive control capability of wind turbine was excavated to meet the grid demand by adjusting active power before wind speed variation, and the reduced active power of wind farms is optimally compensated by thermal powers. Finally, the method was proven to solve voltage problems.

With the development of large wind farms, the voltage problem caused by the power changes of wind farms occurs continuously because of the wind speed variation. The problem cannot be resolved by extra reactive power compensation because of the limitations in cooperation and response speed. A doubly fed induction generator (DFIG) possesses the power decoupling control capability, which can be used to prevent the voltage change rapidly. However, the dynamic processes of the power demands of the grid and the power limits of the DFIG have not been considered. Therefore, a vector equivalent model of the DFIG considering the controllability of the rotor voltage is established. The feasible power ranges that are limited by the electromagnetic process and controller response are deduced. The dynamic requirement and limitation of the reactive power under the wind speed variation are investigated. The emergency control strategy of reactive power contributed by the DFIG is proposed on the basis of the requirement and limitation. The simulation shows that the rapid adjustment capability of the DFIG can be fully utilised by the proposed method.

The complex interactions between AC/DC systems and different line-commutated converter-based high-voltage direct current (LCC-HVDC) expand the effect of commutation failure (CF). The rapid prediction of CF is crucial in ensuring the stable operation of such systems. The simultaneous CF caused by grid fault has received widespread attention in recent years. However, the coupling between the LCC-HVDC with CF and the adjacent normal LCC-HVDC is not considered. When the state of the main circuit suddenly changes and the control system subsequently starts, the LCC-HVDC with CF inevitably produces an effect on the adjacent LCC-HVDC through the coupling of grid voltage. This study describes a new phenomenon, where the former produces a successive CF in the latter under the fault of weak receiving-end grid. The dynamic reactive power characteristics of inverter station and the induced mechanism of successive CF are analyzed. And the dynamic reactive power model of LCC-HVDC is established. A fast prediction method for successive CF is then proposed by calculating the extinction angle of LCC-HVDC with consideration of the effect of adjacent LCC-HVDC with CF. The proposed method can improve the accuracy of CF prediction in multi-infeed LCC-HVDC systems through theoretical derivation and simulation verification.

Aims: To investigate the association between glucose and insulin metabolism and migraine, as well as between diabetes mellitus (DM) and migraine, at a Chinese community level. Methods: A community-based, case-control study was performed in Heihe City, China. A survey was conducted door to door by eight trained investigators. Migraine was diagnosed using the International Classification of Headache Disorders (ICHD-III) beta criteria. A total of 2,023 participants completed a questionnaire, underwent a physical examination, and donated fasting blood. After excluding 191 with reported DM, 1,832 participants were included in the study. Of these, 86 participants with migraine and 95 without migraine participated in a 75-g oral glucose tolerance test. Glycosylated hemoglobin (HbA1c) was assessed at 0 minutes and serum glucose and insulin levels were measured at 0, 30, 60, and 120 minutes after glucose loading. Data with skewed distributions were compared using rank sum test, and the associations between DM and migraine were analyzed with logistic regression. Results: There were no significant differences in HbA1c, homeostatic model assessment-insulin resistance (HOMA-IR), β-cell function index of HOMA, or quantitative insulin sensitivity check index (QUICKI) between the participants with migraine and without migraine. When participants without migraine were classified into DM, prediabetes, and normal glucose subgroups and compared with the corresponding migraine subgroups, participants in the migraine subgroup with prediabetes presented higher levels of fasting insulin and HOMA-IR and a lower QUICKI than the nonmigraine subgroup with prediabetes. Moreover, DM was negatively associated with migraine in the 181 subjects who participated in the OGTT; however, no association was found when all 1,832 participants were considered. Conclusion: Insulin resistance seems to exist in individuals with both migraine and prediabetes, and there is a possible negative association between DM and migraine.

As loads connected to active distribution network (ADN) grow, ADN’s voltage safety issues are becoming more serious. At present, the solution is mainly to build more distributed generation (DG) or to adjust the reactive power in the whole network, but the former needs a lot of investment while the latter requires a large amount of communication equipment and it takes a long time to calculate the adjustment amount of reactive power and to coordinate reactive power compensation equipment. When the loads are heavy, there will still be drawbacks of insufficient reactive power. Therefore, this paper analyzes the relationship between the active power, reactive power, and the voltage in the ADN. Through the autonomous region (AR) division, a voltage control method based on the active power variation and adjustable power in the AR is proposed. According to the relationship between the amount of active power and the adjustable amount active power, the active power control, the reactive power control, and the coordinated control of active power reactive power control are adopted to adjust the DGs’ output to stabilize the bus voltage. The simulation results show that the proposed method can effectively improve the voltage control capability of ADN and can enable it to operate normally under greater power changes. Through the control method in this paper, the communication requirements are greatly reduced and the calculation time is effectively shortened and is more adaptable.

Chinese huge low-cost labor force provided motive power for the development of construction industry in the past decades. However, Chinese labor costs soar quickly in recent years, which bring pressures to construction enterprises. In order to analyze the problems of rising labor costs of Chinese construction industry in depth, a questionnaire survey is conducted among construction workers and project managers. According to the result of the investigation and statistical data, the rising actuality and influence factors of labor costs in Chinese construction industry are analyzed comprehensively. Then the medium and long term prediction of labor cost is carried out by using GM (1, 1) grey model. The results show that the average pay of Chinese construction workers rose quickly over the past 5 years. Changes of supply–demand relation of labor force, soaring prices and the rapid economic development, and other aspects are the reasons causing the labor costs increase. The average daily pay of Chinese construction workers will keep rising in coming years, and will achieve 337 RMB yuan by 2020. The research results present valuable reference basis for construction enterprises to grasp the development trend of labor costs and takes steps to address the labor cost pressures.

Chinese construction companies have experienced dramatic rises in labour wages in recent years. The control and management of construction labour costs are becoming increasingly significant, but the concerns remain secondary in the country. An integrated evaluation index system was established for the labour costs in this paper. Principle component analysis was adopted to study the Chinese construction labour costs between the period 1996 and 2010. The results indicated that labour prices continued to increase from 1996 in China; in 2004 especially, the growth rate accelerated. Meanwhile, the input–output efficiency of the Chinese labour costs increased significantly, and the relative labour costs dropped. The labour costs of the Chinese construction industry presented a beneficial development trend. In an effort to further upgrade the comprehensive level of labour costs in the country, the structure should be further optimised and production mode of construction industry changed.