Correlation between Electrodiagnostic Study and Magnetic Resonance Imaging in Lumbar Radiculopathy Patients in a Tertiary Care Hospital

Background: Involvement of lumbar spinal nerve root, revealed as pain, numbness or weakness in the lower limbs. Typically caused by the compression of nerve at the spine level. Objective: The purpose of the study was to examine the patients with clinically presumed lumbar radiculopathy and find the correlation between their electrodiagnostic study and magnetic resonance imaging. Setting, duration and study type: Retrospective cross-sectional study of one year (January 2019 - February 2020) in Shifa International Hospital Islamabad. Methods: A total of 96 patients with clinically suspected lumbar radiculopathy were included. Chi-square test, international business machines (IBM) SPSS rendition 21.0 was applied on the clinical information, electrodiagnostic study and MRI were coordinated and affectability and particularity were judged. Selected patients were undergone both electrodiagnostic study and magnetic imaging resonance in the selected 1-year span. The study investigated correlation between both diagnostic tools in lumbar radiculopathy patients. Expected outcomes: Anatomical specificity in seen through magnetic resonance imaging while physiological through electrodiagnostic study, which may not correlate in the evaluation of lumbar radiculopathy.

Impact of Synchronous Condenser on the Dynamic Behavior of LCC-based UHVDC System Hierarchically Connected to AC System

Hierarchical connection(HC)is a very attractive mode for±800 kV line commutated converter based ultra high voltage direct current(LCC-UHVDC)system connected to different AC voltage levels because of its ability to reduce the scale factor of a converter transformer.Faults in the HC-UHVDC system can cause commutation failure(CF).In this paper,impact of synchronous condenser(SC)to mitigate CF in HC-UHVDC system is analyzed.A±800KV HC-UHVDC system along with synchronous condenser is built in PSCAD/EMTDC.Transient performance analysis of HC-UHVDC for single and three phase to ground faults is investigated.Commutation failure immunity index(CFII),commutation failure probability index(CFPI),fault recovery time(FRT),and transient overvoltage(TOV)are used as measures to evaluate the effects of SC at HC-UHVDC system design.The simulation results show that SC can make the HCUHVDC system less susceptible to CF,effectively improve fault recovery performances of the overall system,and reduce transient overvoltage when single or multiple converters are blocked.The results of this research can provide technical assistance in real world HC-UHVDC projects.

Dynamics and Small Signal Stability Analysis of PMSG-based Wind Farm with an MMC-HVDC System

The permanent magnet synchronous generator (PMSG)-based wind farm with a modular multilevel converter (MMC) based HVDC system exhibits various oscillations and can experience dynamic instability due to the interactions between different controllers of the wind farm and MMC stations, which have not been properly examined in the existing literatures. This paper presents a dynamic modeling approach for small signal stability analysis of PMSG-based wind farms with a MMC- HVDC system. The small signal model of the study system is validated by the comprehensive electromagnetic transient (EMT) simulations in PSCAD/EMTDC. Then the eigenvalue approach and participation factors analysis are utilized to comprehensively evaluate the impact of different controllers, system’s parameters and the circulating current suppressing controller (CCSC) on the small signal stability of the entire system. From eigenvalue analysis, it is revealed that as the output active power of the wind farm increases within the rated range, the overall system will exhibit a sub-synchronous oscillation (SSO) instability mode, an extremely weak damping mode, and a low frequency oscillation instability mode. From participation factors analysis, it is observed that the SSO mode and weak damping mode are primarily related to the internal dynamics of the MMC, which can be suppressed or improved by CCSC. It is determined that the low frequency oscillation mode is primarily caused by the interactions between the phase locked loop (PLL) control of the wind farm and the voltage and frequency (V-F) control of the MMC station. The analysis also depicts that the larger proportional gain value of the V-F control of the MMC station and smaller PLL bandwidth of the wind farm can enhance the small signal stability of the entire system.

Energy Management System Design and Testing for Smart Buildings Under Uncertain Generation (Wind/Photovoltaic) and Demand

This study provides details of the energy management architecture used in the Goldwind microgrid test bed. A complete mathematical model, including all constraints and objectives, for microgrid operational management is first described using a modified prediction interval scheme. Forecasting results are then achieved every 10 min using the modified fuzzy prediction interval model, which is trained by particle swarm optimization.A scenario set is also generated using an unserved power profile and coverage grades of forecasting to compare the feasibility of the proposed method with that of the deterministic approach. The worst case operating points are achieved by the scenario with the maximum transaction cost. In summary, selection of the maximum transaction operating point from all the scenarios provides a cushion against uncertainties in renewable generation and load demand.