Interlink hybrid DC circuit breaker

—To protect HVDC grids from DC faults, the concept of a hybrid DC circuit breaker is widely accepted due to its low conduction losses and fast interruption speed. For a well-built DC grid, a massive number of hybrid DC circuit breakers have to be installed. This will lead to high capital costs. An interlink DC circuit breaker based on an idea of sharing main breaker branch between two circuit breakers is proposed to reduce the overall costs of circuit breakers in a DC grid. Comparing with existing hybrid DC circuit breakers, the interlink hybrid DC circuit breaker can achieve the same DC fault interruption capability with fewer components. Novel structures of main breaker branches are designed and their parameters are determined to make the interlink hybrid DC circuit breakers be capable for both unidirectional and bidirectional interruption on demand. For a unidirectional interlink hybrid DC circuit breaker, the size of MOVs is reduced by 50%. For a bidirectional interlink hybrid HVDC circuit breaker, the number of IGBTs and MOVs are reduced by 25%. The interlink hybrid DC breakers are verified and compared to the hybrid DC circuit breaker via a three-terminal HVDC grid in PSCAD/EMTDC

Tuning method of a grid-following converter for the extremely-weak-grid connection

This paper proves that a grid-following converter can stably connect to a weak grid even short-circuit ratio (SCR) is 1. Root instability causes of this grid-following control are identified including fast control response, insufficient damping, and slow voltage support. A simple and effective tuning guideline is proposed to stabilize this connection. Three control modes are considered in this tuning guideline including current control, active power and voltage (PV) control, and active power and reactive power (PQ) control . The switching model of a two-level converter is used for the simulation validation

A multi-function integrated circuit breaker for DC grid applications

The protection and current flow regulation of highvoltage direct-current (HVDC) grids requires the deployment of additional semiconductor-based equipment including dc circuit breakers (DCCBs) and current flow controllers (CFCs). However, the inclusion of multiple devices could significantly increase the total cost of an HVDC system. To potentially reduce costs, this paper presents an innovative multi-function integrated DCCB (MF-ICB). The proposed device exhibits a reduced number of semiconductor switches and can fully block dc faults at different locations while regulating dc currents. The configuration of the integrated solution and its operating principle are assessed, with its performance being examined in PSCAD/EMTDC using a three-terminal HVDC grid. Simulation results demonstrate the capability and effectiveness of the MF-ICB to regulate grid current and isolate dc faults

A multi-function integrated circuit breaker for DC grid applications

The protection and current flow regulation of highvoltage direct-current (HVDC) grids requires the deployment of additional semiconductor-based equipment including dc circuit breakers (DCCBs) and current flow controllers (CFCs). However, the inclusion of multiple devices could significantly increase the total cost of an HVDC system. To potentially reduce costs, this paper presents an innovative multi-function integrated DCCB (MF-ICB). The proposed device exhibits a reduced number of semiconductor switches and can fully block dc faults at different locations while regulating dc currents. The configuration of the integrated solution and its operating principle are assessed, with its performance being examined in PSCAD/EMTDC using a three-terminal HVDC grid. Simulation results demonstrate the capability and effectiveness of the MF-ICB to regulate grid current and isolate dc faults

Coordination of MMCs with hybrid DC circuit breakers for HVDC grid protection

A high-voltage direct-current (HVDC) grid protection strategy to suppress dc fault currents and prevent overcurrent in the arms of modular multi-level converters (MMCs) is proposed in this paper. The strategy is based on the coordination of half-bridge (HB) MMCs and hybrid dc circuit breakers (DCCBs). This is achieved by allowing MMC submodules (SMs) to be temporarily bypassed prior to the opening of the DCCBs. Once the fault is isolated by the DCCBs, the MMCs will restore to normal operation. The performance of the proposed method is assessed and compared to when MMCs are blocked and when no corrective action is taken. To achieve this, an algorithm for fault detection and discrimination is used and its impact on MMC bypassing is discussed. To assess its effectiveness, the proposed algorithm is demonstrated in PSCAD/EMTDC using a four-terminal HVDC system. Simulation results show that the coordination of MMCs and DCCBs can significantly reduce dc fault current and the absorbed current energy by more than 70 and 90% respectively, while keeping MMC arm currents small

Operation and control of an HVDC circuit breaker with current flow control capability

Deployment of dc circuit breakers (DCCBs) will help to isolate dc faults in dc systems. Conversely, current flow controllers (CFCs) will be employed in dc grids to balance currents among transmission lines. However, the inclusion of these devices may incur significant capital investment. A way to reduce costs is by integrating current control capabilities into DCCBs. This paper presents a new device, the CB/CFC, which combines a multi-line DCCB with a half-bridge based CFC. The operating principles of the device are analyzed and its operating modes are classified. A level-shift modulation method ensuring that a single bridge of the CB/CFC is modulated for each operating mode is considered. This simplifies the control scheme for CFC operation. For completeness, the CB/CFC is compared with other alternatives available in the literature. It is shown that the presented device reduces the number of semiconductor components compared to other solutions. DC fault isolation and current flow control are verified through simulations conducted in PSCAD

Dominant instability mechanism of VSI connecting to a very weak grid

In this paper, it is identified that unstable weak grid connection of voltage source inverters (VSIs) is dominantly caused by the current control. In particular, it is found the proportional gain k p of conventional PI controller cannot balance the grid voltage impact and damping capability when a weak grid with short circuit ratio (SCR) < 1.3 is connected. This issue is solved in this paper by simply restructuring the PI controller as an IP controller for current control. This IP controller will not change the tuning method of current control and make this VSI indeed connect to a very weak grid with rated power injection

Effect of rs1344706 in the ZNF804A gene on the brain network.

ZNF804A rs1344706 (A/C) was the first SNP that reached genome-wide significance for schizophrenia. Recent studies have linked rs1344706 to functional connectivity among specific brain regions. However, no study thus far has examined the role of this SNP in the entire functional connectome. In this study, we used degree centrality to test the role of rs1344706 in the whole-brain voxel-wise functional connectome during the resting state. 52 schizophrenia patients and 128 healthy controls were included in the final analysis. In our whole-brain analysis, we found a significant interaction effect of genotype&nbsp;×&nbsp;diagnosis at the precuneus (PCU) (cluster size&nbsp;=&nbsp;52 voxels, peak voxel MNI coordinates: x&nbsp;=&nbsp;9, y&nbsp;=&nbsp;-&nbsp;69, z&nbsp;=&nbsp;63, F&nbsp;=&nbsp;32.57, FWE corrected P&nbsp;&lt;&nbsp;0.001). When we subdivided the degree centrality network according to anatomical distance, the whole-brain analysis also found a significant interaction effect of genotype&nbsp;×&nbsp;diagnosis at the PCU with the same peak in the short-range degree centrality network (cluster size&nbsp;=&nbsp;72 voxels, F&nbsp;=&nbsp;37.29, FWE corrected P&nbsp;&lt;&nbsp;0.001). No significant result was found in the long-range degree centrality network. Our results elucidated the contribution of rs1344706 to functional connectivity within the brain network, and may have important implications for our understanding of this risk gene's role in functional dysconnectivity in schizophrenia

Evidence for the contribution of COMT gene Val158/108Met polymorphism (rs4680) to working memory training-related prefrontal plasticity.

BackgroundGenetic factors have been suggested to affect the efficacy of working memory training. However, few studies have attempted to identify the relevant genes.MethodsIn this study, we first performed a randomized controlled trial (RCT) to identify brain regions that were specifically affected by working memory training. Sixty undergraduate students were randomly assigned to either the adaptive training group (N&nbsp;=&nbsp;30) or the active control group (N&nbsp;=&nbsp;30). Both groups were trained for 20 sessions during 4&nbsp;weeks and received fMRI scans before and after the training. Afterward, we combined the data from the 30 participants in the RCT study who received adaptive training with data from 71 additional participants who also received the same adaptive training but were not part of the RCT study (total N&nbsp;=&nbsp;101) to test the contribution of the COMT Val158/108Met polymorphism to the interindividual difference in the training effect within the identified brain regions.ResultsIn the RCT study, we found that the adaptive training significantly decreased brain activation in the left prefrontal cortex (TFCE-FWE corrected p&nbsp;=&nbsp;.030). In the genetic study, we found that compared with the Val allele homozygotes, the Met allele carriers' brain activation decreased more after the training at the left prefrontal cortex (TFCE-FWE corrected p&nbsp;=&nbsp;.025).ConclusionsThis study provided evidence for the neural effect of a visual-spatial span training and suggested that genetic factors such as the COMT Val158/108Met polymorphism may have to be considered in future studies of such training

Sex differences in erythrocyte fatty acid composition of first-diagnosed, drug-naïve patients with major depressive disorders

Background: Since depression, sex hormones, and fatty acid status are interrelated, it is important to understand their relationships. In this study, we aimed to investigate sex differences in erythrocyte membrane fatty acid composition among first-diagnosed, drug-naïve patients with major depressive disorders.Methods: The study included 139 individuals with first-diagnosed, drug-naïve depression (male/female = 48/91) and 55 healthy controls (male/female = 24/31). The levels of erythrocyte membrane fatty acids were analyzed to compare the difference between males and females in both patients with depression and healthy controls, as well as to study their correlation with depressive symptoms.Results: In first-diagnosed, drug-naïve patients with major depressive disorders, sex disparities were observed in the levels of erythrocyte saturated fatty acids (SFAs) and n-6 PUFAs (such as C18:0, C20:4n6 and C22:4n6), where higher levels evident in females compared to in males. We found a noteworthy correlation between fatty acid levels and depressive symptoms, in which there is a significant association between female patients and depression but a weaker association between male patients and depression.Conclusion: Our findings demonstrate higher levels of n-6 PUFAs and SFAs in female patients with depression. The relationship between fatty acid composition and depressive symptoms was more prominent in females than males. These findings highlight the significance of considering sex as a crucial and interconnected factor in future investigations and potential adjunctive treatment for mood disorders by targeting fatty acid metabolism