Dual harmonic injection for reducing the sub-module capacitor voltage ripples of hybrid MMC

Reducing the capacitor voltage ripples of the half-bridge sub-modules (HBSM) and full-bridge sub-modules (FBSM) in a hybrid modular multilevel converter (MMC) is expected to reduce the capacitance, volume and costs. To address this issue, this paper proposes a dual harmonic injection method which injects the second harmonic circulating current and third order harmonic voltage into the conventional MMC control. Firstly, the mathematical model of the proposed control is established and analyzed. Then, the general strategy of determining the amplitude and phase angle of each injection component is proposed to suppress the fluctuations of the fundamental and double frequency instantaneous power. The proposed strategy can achieve the optimal power fluctuation suppression under various operating conditions, which also has the advantage of reducing the voltage fluctuation difference between HB and FB SMs. The correctness and effectiveness of the proposed strategy are verified in simulations in PSCAD/EMTDC

The association between physical activity and anxiety in college students: parallel mediation of life satisfaction and self-efficacy

ObjectiveTo explore the functions that physical activity (PA), life satisfaction, and self-efficacy have in the process of coping with anxiety among Chinese college students, and to explore the mediating role of life satisfaction and self-efficacy in this process.MethodsParticipants were 358 college students (186 males, 172 females, mean age 20.88, SD = ±1.80). Psychosocial tests including the Physical Activity Rating Scale (PARS-3), College Student Life Satisfaction Scale (CSLSS), General Self-Efficacy Scale (GSES), and Generalized Anxiety Disorder Scale (GAD-7) were completed. Correlations between variables were calculated using Pearson’s test. The mediation model was tested using the SPSS 26.0 PROCESS macro and regression bootstrap.ResultsPhysical activity showed a negative correlation with anxiety (β = −0.1617, p < 0.001., life satisfaction and self-efficacy played a role in the relationship between physical activity and anxiety. More importantly, physical activity was associated with anxiety through parallel mediating effects of life satisfaction and self-efficacy, with a total mediating effect of 55.34%.ConclusionBy increasing college students’ participation in physical activity, it helps to promote the growth of their life satisfaction and self-efficacy, which is the key to reducing anxiety and promoting college students’ mental health

Optimal second-harmonic current injection for capacitor voltage fluctuation reduction in hybrid MMCs under grid-side SLG faults

The second-harmonic injection strategy for modular multilevel converters (MMCs) can effectively suppress the capacitor voltage fluctuation in steady states. However, the capacitor voltage fluctuation under grid-side single-line-to-ground (SLG) faults will be more severe. Moreover, there is no research on the mitigation of capacitor voltage fluctuation under grid-side SLG faults for the hybrid MMC with mixed half-bridge and full-bridge sub-modules. To address this issue for hybrid MMCs, an optimal second-harmonic current injection scheme for mitigating the capacitor voltage fluctuation in the hybrid MMC under grid-side SLG faults is proposed in this paper. The mathematical models of arm power fluctuations of the hybrid MMC are firstly developed under both steady states and grid-side SLG faults. Then, the principle and optimal strategy of the proposed capacitor voltage fluctuation strategy are presented. The capacitor voltage fluctuation under grid-side SLG faults can be reduced by suppressing the three-phase arm power fluctuations. A hybrid MMC model with the proposed scheme has been established in PSCAD/EMTDC to verify its effectiveness and feasibility. Simulation results show that the average voltage fluctuation reduction rate can reach 55.77% with the proposed strategy

The potential microalgae-based strategy for attaining carbon neutrality and mitigating climate change: a critical review

In recent years, the impacts of global warming, including glacial melting, extreme weather events, food crises, and epidemics, have become increasingly severe, posing significant challenges to global sustainability. The primary driver of the current climate crisis is the substantial emission of greenhouse gases (GHGs), particularly carbon dioxide (CO2). Microalgae, as photoautotrophic microorganisms, offer a promising solution by utilizing CO2 for biosynthesis. Previous research indicates that microalgae can fix CO2 at rates exceeding 1.5 kg/m2/year under optimal conditions, and produce lipids with high content of unsaturated fatty acids. This review delves into recent advancements understanding the causes and effects of global warming, with a particular focus on agricultural GHG emissions. It critically examines the carbon sequestration mechanisms of microalgae and their potential as single-cell biofactories for carbon neutralization and biomanufacturing. The review highlights their ability to fix CO2 and produce high-value products such as biofuels, chemicals, pharmaceuticals, and foods. Among these species, the characteristics and value of seven edible microalgae are also described. We outline the technical and economic challenges associated with scaling up microalgae cultivation from laboratory to industrial scale, including the optimization of cultivation systems and the improvement of harvesting and processing techniques. This review serves as a useful and informative reference for the application of CO2 capture and high-value bioproducts by microalgae, aiming to provide a reference for the realization of carbon neutrality and the mitigation of climate change

The influence of physical exercise on negative emotions in adolescents: a meta-analysis

BackgroundAdolescence is also accompanied by ongoing mood changes (relative to childhood and adulthood), which can trigger more extreme negative emotional responses. Physical exercise alleviates negative emotions and reduces the risk of mental illness. However, the effect of physical exercise on negative emotions in adolescents is unclear, so it is valuable to synthesize previous studies with meta-analysis.ObjectiveTo examine the influence of physical exercise (PE) intervention on negative emotions in adolescents aged 10 to 19 years.MethodsWe retrieved the articles from PubMed, Web of Science, EBSCO, Cochrane, and Embase up to April 11, 2024. The main search terms were physical exercise, negative emotions, adolescents, randomized controlled trials. The meta-analysis was conducted using Review Manager 5.3. A random-effects model was employed to calculate the standardized mean difference (SMD) and 95% confidence interval (CI). Subgroups were analysed as the type of negative emotions, type of control group, intervention type, duration, time, frequency.ResultsThe PE intervention group exhibited a significantly superior improvement in alleviating negative emotions compared to the control group (SMD = -0.59, 95% CI: -0.92 to -0.26, p < 0.01, Z = 3.50, I² = 95%). PE was particularly effective in mitigating adolescent depression (SMD = -0.67, 95% CI = -1.07 to -0.28, p < 0.01, I² = 96%) but did not yield significant results in reducing adolescent anxiety (SMD = -0.29, 95% CI = -0.63 to 0.05, p = 0.10, I² = 95%).ConclusionPE intervention can ameliorate negative emotions in adolescents.Systematic Review Registrationhttps://www.crd.york.ac.uk/prospero/, identifier CRD42024534375