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In this paper, the cascaded H-bridge (CHB) multilevel inverter is employed as a grid connected inverter. This kind of inverter has interesting features compared to conventional inverters, including better efficiency, lower THD, lower common mode current injection, and better waveform quality. Using a series connection of H-bridge cells in this topology, a high modularity is achieved and a stepwise voltage waveform is synthesized at the ac side, leading to lower filter size and complexity. This topology processes the electric power in one stage and does not need any step-up voltage transformer for grid connection. The dynamic performance of control system is studied through simulations and is compared with the conventional approach. In addition, a new voltage estimation approach is proposed to reduce the number of voltage sensors compared to existing methods. The simulation results are presented for a 1.5 kW grid connected 7-level CHB inverter and then the hardware-in-the-loop implementation of the CHB inverter is presented to verify the performance of control system.

This study presents a novel time-domain protection technique for application to DC grids. The technique utilises the power developed by the forward and backward travelling waves produced by a fault to distinguish between internal and external faults. For an internal fault, the calculated travelling wave power must exceed a predetermined setting; otherwise the fault is external. The ratio between the forward travelling wave power and the backward travelling wave power provides a directional comparison. For a forward directional fault, this ratio is less than unity, whereas the ratio is greater than unity for reverse directional faults. To improve the sensitivity of the protection scheme for long-distance remote internal fault, a second element utilising the concavity of the forward travelling wave power is proposed. The proposed technique is time domain based and does not require complex mathematical burden; moreover, as such can be easily implemented since it will require fewer hardware resources. Simulations were carried out in power systems computer-aided design/electromagnetic transient simulations, and the results presented considering wider cases of fault scenarios including 500 Ω remote internal fault shows the suitability of the proposed scheme as all fault scenarios indicated were identified within 500 µs following the application of the fault.

Assessment of host response to inflammation will throw light on the critical role of antioxidants (AOs) and free radicle damage in the etiology of periodontal disease. The purpose of the study was to assess the level of plasma oxidative stress in those having aggressive periodontal disease before and after full-mouth disinfection. Objectives were to find the influence of full-mouth disinfection analyzing the level of thiobarbituric acid reactive substances (TBARSs), thereby quantifying the lipid peroxidation (LPO) and also the activities of reduced glutathione (GSH), glutathione peroxidase (GPThe valuation composed of 30 subjects with aggressive periodontal disease and 30 healthy controls. Clinical assessment included following periodontal parameters: plaque index (PI), papillary bleeding index (PBI), probing pocket depth (PPD), and clinical attachment level (CAL). Levels of bone loss were assessed by taking full-mouth periapical radiographs. Initial periodontal therapy comprises of full-mouth disinfection which includes subgingival scaling and root planing within 24 hours combined with adjunctive chlorhexidine chemotherapy for aggressive periodontitis subject's at sites indicated. The parameters (clinical) were evaluated at the baseline and 8 weeks after initial periodontal therapy at six sites of teeth indicated. Plasma samples were taken and evaluated by standard procedures as defined in the literature. All the values were weighed and related.Strong positive associations were detected among periodontal parameters and TBARS, enzymatic/nonenzymatic AO levels (This paper evaluated ROS activity and AO defense before and after treatment to stimulate added periodontal investigation in this part which will give an insight into the therapeutic options with foreseeable results.

This paper presents a transient based protection principle utilising the magnitude of the travelling wave power derivative at only local terminal to formulate a non-unit protection scheme, where the directional transient relay and boundary relay have been involved. In terms of boundary relay, for an internal fault in the forward direction with respect to a local relay, the traveling wave power derivative will exceed a pre-determined setting, otherwise the fault is external to the relay, due to the discontinuity of surge impedance at the boundary point. Directional detection is achieved by the comparison of the forward travelling wave power to the backward travelling wave power. The ratio of forward traveling wave to backward traveling wave is less than unity for all forward directional faults and much greater than unity for reverse directional faults. Simulation studies carried out in PSCAD and the results presented shows the suitability of the proposed protection principle as all fault scenario indicated were detected within 250μs following the application of the faults.

Modular multilevel converters (MMCs) will be extensively used in the high-voltage direct-current transmission networks because of its superior characteristics over line commutated converter. Increasing the reliability of the MMC is directly related to the balancing of the MMC submodule capacitors voltages, which guarantees the proper operation of the converter and lowers the stress on the submodules. This paper presents an adaptive voltage-balancing strategy based on the capacitor voltage estimation, utilizing a hybrid adaptive linear neuron recursive least squares scheme. The proposed strategy eliminates the need of measuring submodules capacitor voltages and associated communication link with the central controller. Furthermore, the estimated capacitor voltages are utilized to detect and localize different types of submodule faults. After isolating the faulty submodules, the proposed fault-tolerant control unit modifies the parameters of the voltage-balancing strategy to overcome the reduction of the active submodules. The dynamic performance of the proposed strategy is investigated, using PSCAD/EMTDC simulations and hardware-in-the-loop real-time simulations, under different normal and faulty operating conditions. The accuracy and the time response of the proposed fault detection and tolerant control units result in stabilizing the operation of the MMC under different types of faults. Consequently, the proposed integrated control strategy improves the reliability of the MMC.

A DC-DC converter suitable for the grid integration of windfarms through a DC grid is presented. The operation is based on the Marx principle where charged capacitors are connected in series and parallel in turn to achieve the voltage transformation. The two inductors at the two ends of the converter are designed to resonate with the capacitors to create resonance forcing current zeros to enable zero current switching thereby reducing switching losses. The design of a 50 MW, 6kV/30kV DC-DC converter was carried out by analysis and simulation

Electrical power to data hall critical loads will often be fed via an uninterruptable power supply (UPS) strings. Therefore, fault tolerance of these machines is of pivotal importance for the data centres uptime. The UPS will be in the middle of a complex electrical distribution system with reliance on other connected components for optimal performance. The data centre owners will also want to know what happens when components on the UPS power string fail and what effects this can have on critical equipment's. The goal is to minimise any negative effective on critical power and achieve 100% operational uptime. This paper investigates a rotary UPS string in terms of fault currents, electrical protection and arc flash.

Background Familial hypercholesterolemia ( FH ), is a historically underdiagnosed, undertreated, high‐risk condition that is associated with a high burden of cardiovascular morbidity and mortality. In this study, we use a population‐based approach using electronic health record ( EHR )‐based algorithms to identify FH . We report the major adverse cardiovascular events, mortality, and cost of medical care associated with this diagnosis. Methods and Results In our 1.18 million EHR‐ eligible cohort, International Classification of Diseases, Ninth Revision ( ICD ‐9 ) code‐defined hyperlipidemia was categorized into FH and non‐ FH groups using an EHR algorithm designed using the modified Dutch Lipid Clinic Network criteria. Major adverse cardiovascular events, mortality, and cost of medical care were analyzed. A priori associated variables/confounders were used for multivariate analyses using binary logistic regression and linear regression with propensity score–based weighted methods as appropriate. EHR FH was identified in 32 613 individuals, which was 2.7% of the 1.18 million EHR cohort and 13.7% of 237 903 patients with hyperlipidemia. FH had higher rates of myocardial infarction (14.77% versus 8.33%; P P P P P Conclusions EHR ‐based algorithms discovered a disproportionately high prevalence of FH in our medical cohort, which was associated with worse outcomes and higher costs of medical care. This data‐driven approach allows for a more precise method to identify traditionally high‐risk groups within large populations allowing for targeted prevention and therapeutic strategies.

The increasing demand for high voltage DC grids resulting from the continuous installation of offshore wind farms in the North Sea has led to the concept of multi-terminal direct current (MTDC) grids, which face some challenges. Power (current) flow control is a challenge that must be addressed to realize a reliable operation of MTDC grids. This paper presents a reduced switch count topology of a current flow controller (CFC) for power flow and current limiting applications in MTDC grids. A simple control system based on hysteresis band current control is proposed for the CFC. The theory of operation and control of the CFC are demonstrated. The key features of the proposed controller, including cable current balancing, cable current limiting, and current nulling, are illustrated. An MTDC grid is simulated using MATLAB/SIMULINK software to evaluate the steady state and dynamic performance of the proposed CFC topology. Furthermore, a low power prototype is built for a CFC to experimentally validate its performance using rapid control prototyping. Simulation and experimental studies indicate the fast dynamic response and precise results of the proposed topology. Furthermore, the proposed controller offers a real solution for power flow challenges in MTDC grids.

One of the main problems that need to be solved to allow the realisation of multi-terminal high-voltage direct current (HVDC) transmission systems is the absence of a practical power flow control method. Industry leaders and researchers have proposed a few methods of power flow control based on either the control of converter station or the connection of new power electronic equipment to the grid. This study presents the operation and control of a three-port insulated gate bipolar transistor-based current flow control (CFC) device suitable for multi-terminal HVDC systems. Key features and functionalities of the proposed controller including the balancing of cable currents, limiting the magnitude of cable current and current nulling are demonstrated. The three-port CFC was simulated using power system computer aided design (PSCAD)/electromagnetic transient and direct current (EMTDC), network simulation software to evaluate its steady state and dynamic performance. Furthermore, low-power prototypes are implemented for a two and three-ports CFC to experimentally validate their different functionalities. Simulation and experimental studies explore the fast dynamic response and the results show that the CFC studied may have a significant role to play in the control of power flows in multi-terminal high-voltage DC systems.

A high voltage DC-DC converter is a key component of future HVDC grids. This paper presents a comparison of a single-stage and multi-stage converter. Both topologies are based on the Marx principle where charged capacitors are charged in parallel and discharged in series to achieve the voltage transformation. Detailed models of both converter topologies at 50 MW, 6kV/72kV are designed and simulated using Matlab/Simulink package software.

This paper is based on an investigation of load flow, short circuit analysis, and load point reliability of a data centres electrical power distribution network. A series of power system analysis software simulations were undertaken in order to determine the steady state behaviours of the power distribution system. Each load flow model investigated allowed a critique of model results for verification of critical bus-bar Voltage Security Index (VSI) and confirmation of acceptable Voltage limits, in-line with industry standards. Load flow studies highlighted optimal configurations for the electrical distribution networks, short circuit faults were simulated at multiple network locations for both nominal grid feeders, and mesh configurations with standby generators. Results from this research paper have provided recommendations on how to improve Operational Availability (AO) with suggestions given for optimal equipment configuration in terms of achieving improved Voltage security, limiting the required short circuit ratings of network equipment and investigating the improvement of load point reliability.

In order to reduce the cost and visual impact of electrified railway lines, radical changes in infrastructure can be avoided by only removing the catenary wire. This can produce a significant saving in the overall cost of the railway network, reduce maintenance requirements and improve the overall visual impact. On-board energy storage systems have a significant role in providing the required energy during catenary free operation of trams, and in the recovery of regenerated energy from braking. It was found that a 13km journey can be achieved with a battery energy capacity of 39.6kWh with a rated voltage of 495V. Achieving an efficient train control, and optimising the energy management, can improve the energy efficiency of rapid transit systems. This paper presents a novel energy management phase driven method to perform state actions and control the transition between different operating energy supply modes for catenary free tram operation. The StateFlow environment is used to model the energy management, and has been implemented using ANSI C.