Inverter-dominated isolated/islanded microgrids(IDIMGs)lack infinite buses and have low inertia,resulting in higher sensitivity to disturbances and reduced stability compared to grid-tied systems.Enhanc-ing the resili...Inverter-dominated isolated/islanded microgrids(IDIMGs)lack infinite buses and have low inertia,resulting in higher sensitivity to disturbances and reduced stability compared to grid-tied systems.Enhanc-ing the resilience of IDIMGs can be achieved by maxim-izing the system loadability and/or mitigating the expected disturbances such as line switching operations.This paper proposes a two-stage framework based on the deployment of mobile energy storage(MES)to enhance the resilience of IDIMGs.In the first stage,the network configuration and deployment of MES are optimized to maximize the system loadability.The proposed formulation for this stage is a stochastic multi-period mixed-integer nonlinear program(MINLP)that maximizes a weighted sum of minimax loadabilities.In the second stage,transitional locations of MES,line-exchange execution sequence,and droop control of dispatchable sources are jointly optimized to mitigate line-switching disturbances that occur when transitioning to the new network configuration obtained in the first stage.The second stage model is a multi-objective MINLP.The proposed models are solved within the gen-eral algebraic modeling system(GAMS),utilizing a mod-ified IEEE 33-bus system.Simulations are conducted to assess the significance of each proposed model,and the results reveal remarkable improvements in system loadability with the utilization of the first-stage model and significant reductions in the total switched power with the adoption of the second-stage model.展开更多
The multi-voltage-level DC distribution network(MVL-DC-DN)is a promising network for efficiently integrat ing rapidly growing DC loads,and fast-growing load demand would bring a challenge to the MVL-DC-DN in terms of ...The multi-voltage-level DC distribution network(MVL-DC-DN)is a promising network for efficiently integrat ing rapidly growing DC loads,and fast-growing load demand would bring a challenge to the MVL-DC-DN in terms of the maximum loadability.This paper considers the DC electric spring(DC-ES)as a novel candidate flexible resource for en hancing the maximum loadability of the MVL-DC-DN,and pro poses an evaluation method for the maximum loadability.First ly,with the consideration of device constraints,the impact that the DC-ES on the maximum loadability of the DC distribution network(DC-DN)is analyzed via a simplified equivalent cir cuit.Subsequently,the power flow(PF)model of an MVL-DCDN with DC-ESs is established.Finally,a method based on con tinuation power flow(CPF)for evaluating the maximum load ability of an MVL-DC-DN with DC-ESs is proposed.During the evaluation,limitations of the DC-ES and the DC transform er(DCT)are considered.The consideration of the practical con straints avoids the overestimation of the maximum loadability.The case study verifies the effectiveness of the proposed method.展开更多
The increase of energy consumption has caused power systems to operate close to the limit of their capacity.The distributed power flow controller(DPFC),as a new member of distributed flexible AC transmission systems,i...The increase of energy consumption has caused power systems to operate close to the limit of their capacity.The distributed power flow controller(DPFC),as a new member of distributed flexible AC transmission systems,is introduced to remove this barrier.This paper proposes an optimal DPFC configuration method to enhance system loadability considering economic performance based on mixed integer linear programming.The conflicting behavior of system loadability and DPFC investment is analyzed and optimal solutions are calculated.Thereafter,the fuzzy decision-making method is implemented for determining the most preferred solution.In the most preferred solution obtained,the investment of DPFCs is minimized to find the optimal number,locations and set points.Simulation results on the IEEERTS79 system demonstrate that the proposed method is effective and reasonable.展开更多
This paper considers the use of the inherent structural characteristics of power system networks for improving the reactive power reserve margins for both topologically weak and strong networks. The inherent structura...This paper considers the use of the inherent structural characteristics of power system networks for improving the reactive power reserve margins for both topologically weak and strong networks. The inherent structural characteristics of the network are derived from the Schur complement of the partitioned Y-admittance matrix using circuit theory representations. Results show that topologically strong networks, operating close to the upper voltage limit could be made to increase their loadability margin by locating reactive power compensators close to generator sources, whereas topologically weak (ill conditioned) networks could be made to operate within the feasible operating limits by locating reactive power compensators on buses farther from generator sources.展开更多
This paper presents an application of GRADE Algorithm based approach along with PV analysis to solve multi objective optimization problem of minimizing real power losses, improving the voltage profile and hence enhanc...This paper presents an application of GRADE Algorithm based approach along with PV analysis to solve multi objective optimization problem of minimizing real power losses, improving the voltage profile and hence enhancing the performance of power system. GRADE Algorithm is a hybrid technique combining genetic and differential evolution algorithms. Control variables considered are Generator bus voltages, MVAR at capacitor banks, transformer tap settings and reactive power generation at generator buses. The optimal values of the control variables are obtained by solving the multi objective optimization problem using GRADE Algorithm programmed using M coding in MATLAB platform. With the optimal setting for the control variables, Newton Raphson based power flow is performed for two test systems, viz, IEEE 30 bus system and IEEE 57 bus system for three loading conditions. Minimization of Real power loss and improvement of voltage profile obtained are compared with the results obtained using firefly and particle swarm optimization (PSO) techniques. Improvement of Loadability margin is established through PV curve plotted using continuation power flow with the real power load at the most affected bus as the bifurcation parameter. The simulated output shows improved results when compared to that of firefly and PSO techniques, in term of convergence time, reduction of real power loss, improvement of voltage profile and enhancement of loadability margin.展开更多
In a Power System, load is the most uncertain and extremely time varying unit. Hence it is important to determine the system’s supreme acceptable loadability limit called maximum loadability point to accommodate...In a Power System, load is the most uncertain and extremely time varying unit. Hence it is important to determine the system’s supreme acceptable loadability limit called maximum loadability point to accommodate the sudden variation of load demand. Nowadays the enhancement of the maximum loadability point is essential to meet the rapid growth of load demand by improvising the system’s load utilization capacity. Flexible AC Transmission system devices (FACTS) with their speed and flexibility will play a key role in enhancing the controllability and power transfer capability of the system. Considering the theme of FACTS devices in the loadability limit enhancement, in this paper maximum loadability limit determination and its enhancement are prepared with the help of swarm intelligence based meta-heuristic Firefly Algorithm(FFA) by finding the optimal loading factor for each load and optimally placing the SVC (Shunt Compensation) and TCSC (Series Compensation) FACTS devices in the system. To illuminate the effectiveness of FACTS devices in the loadability enhancement, the line contingency scenario is also concerned in the study. The study of FACTS based maximum system load utilization acceptability point determination is demonstrated with the help of modified IEEE 30 bus, IEEE 57 Bus and IEEE 118 Bus test systems. The results of FACTS devices involvement in determining the maximum loading point enhance the load utilization point in normal state and also help to overcome the system violation in transmissionline contingency state. Also the firefly algorithm in determining the maximum loadability point provides better search capability with faster convergence rate compared to that of Particle swarm optimization (PSO) and Differential evolution algorithm.展开更多
The aim of present study was to formulate and evaluate a self-microemulsifying drug delivery systems(SMEDDS)containing lovastatin and to further explore the ability of porous Neusilin■ US2 tablet as a solid carrier f...The aim of present study was to formulate and evaluate a self-microemulsifying drug delivery systems(SMEDDS)containing lovastatin and to further explore the ability of porous Neusilin■ US2 tablet as a solid carrier for SMEDDS.SMEDDS formulations of varying proportions of peceol,cremophor RH 40 and transcutol-P were selected and subjected to invitro evaluation,including dispersibility studies,droplet size,zeta potential measurement and release studies.The results indicated that the drug release profile of lovastatin from SMEDDS formulations was statistically significantly higher(p-value<0.05)than the plain lovastatin powder.Thermodynamic stability studies also confirmed the stability of the prepared SMEDDS formulations.The optimized formulation,which consists of 12% of peceol,44% of cremophor RH 40,and 44% of transcutol-P was loaded into directly compressed liquid loadable tablet of Neusilin■ US2 by simple adsorption method.In order to determine the ability of Neusilin®US2 as a suitable carrier pharmacodynamics study were also carried out in healthy diet induced hyperlipidemic rabbits.Animals were administered with both liquid SMEDDS and solid SMEDDS as well.From the results obtained,Neusilin■ was found to be a suitable carrier for SMEDDS and was equally effective in reducing the elevated lipid profile.In conclusion,liquid loadable tablet(LLT)is predicted to be a promising technique to deliver a liquid formulation in solid state.展开更多
文摘Inverter-dominated isolated/islanded microgrids(IDIMGs)lack infinite buses and have low inertia,resulting in higher sensitivity to disturbances and reduced stability compared to grid-tied systems.Enhanc-ing the resilience of IDIMGs can be achieved by maxim-izing the system loadability and/or mitigating the expected disturbances such as line switching operations.This paper proposes a two-stage framework based on the deployment of mobile energy storage(MES)to enhance the resilience of IDIMGs.In the first stage,the network configuration and deployment of MES are optimized to maximize the system loadability.The proposed formulation for this stage is a stochastic multi-period mixed-integer nonlinear program(MINLP)that maximizes a weighted sum of minimax loadabilities.In the second stage,transitional locations of MES,line-exchange execution sequence,and droop control of dispatchable sources are jointly optimized to mitigate line-switching disturbances that occur when transitioning to the new network configuration obtained in the first stage.The second stage model is a multi-objective MINLP.The proposed models are solved within the gen-eral algebraic modeling system(GAMS),utilizing a mod-ified IEEE 33-bus system.Simulations are conducted to assess the significance of each proposed model,and the results reveal remarkable improvements in system loadability with the utilization of the first-stage model and significant reductions in the total switched power with the adoption of the second-stage model.
基金supported in part by the National Natural Science Foundation of China(No.52077017).
文摘The multi-voltage-level DC distribution network(MVL-DC-DN)is a promising network for efficiently integrat ing rapidly growing DC loads,and fast-growing load demand would bring a challenge to the MVL-DC-DN in terms of the maximum loadability.This paper considers the DC electric spring(DC-ES)as a novel candidate flexible resource for en hancing the maximum loadability of the MVL-DC-DN,and pro poses an evaluation method for the maximum loadability.First ly,with the consideration of device constraints,the impact that the DC-ES on the maximum loadability of the DC distribution network(DC-DN)is analyzed via a simplified equivalent cir cuit.Subsequently,the power flow(PF)model of an MVL-DCDN with DC-ESs is established.Finally,a method based on con tinuation power flow(CPF)for evaluating the maximum load ability of an MVL-DC-DN with DC-ESs is proposed.During the evaluation,limitations of the DC-ES and the DC transform er(DCT)are considered.The consideration of the practical con straints avoids the overestimation of the maximum loadability.The case study verifies the effectiveness of the proposed method.
基金supported in part by the National Natural Science Foundation of China(No.51577030)in part by the project of State Grid Corporation of China(Research on flexible AC power flow control technology of transmission network based on a distributed power flow controller)(No.8516000700).
文摘The increase of energy consumption has caused power systems to operate close to the limit of their capacity.The distributed power flow controller(DPFC),as a new member of distributed flexible AC transmission systems,is introduced to remove this barrier.This paper proposes an optimal DPFC configuration method to enhance system loadability considering economic performance based on mixed integer linear programming.The conflicting behavior of system loadability and DPFC investment is analyzed and optimal solutions are calculated.Thereafter,the fuzzy decision-making method is implemented for determining the most preferred solution.In the most preferred solution obtained,the investment of DPFCs is minimized to find the optimal number,locations and set points.Simulation results on the IEEERTS79 system demonstrate that the proposed method is effective and reasonable.
文摘This paper considers the use of the inherent structural characteristics of power system networks for improving the reactive power reserve margins for both topologically weak and strong networks. The inherent structural characteristics of the network are derived from the Schur complement of the partitioned Y-admittance matrix using circuit theory representations. Results show that topologically strong networks, operating close to the upper voltage limit could be made to increase their loadability margin by locating reactive power compensators close to generator sources, whereas topologically weak (ill conditioned) networks could be made to operate within the feasible operating limits by locating reactive power compensators on buses farther from generator sources.
文摘This paper presents an application of GRADE Algorithm based approach along with PV analysis to solve multi objective optimization problem of minimizing real power losses, improving the voltage profile and hence enhancing the performance of power system. GRADE Algorithm is a hybrid technique combining genetic and differential evolution algorithms. Control variables considered are Generator bus voltages, MVAR at capacitor banks, transformer tap settings and reactive power generation at generator buses. The optimal values of the control variables are obtained by solving the multi objective optimization problem using GRADE Algorithm programmed using M coding in MATLAB platform. With the optimal setting for the control variables, Newton Raphson based power flow is performed for two test systems, viz, IEEE 30 bus system and IEEE 57 bus system for three loading conditions. Minimization of Real power loss and improvement of voltage profile obtained are compared with the results obtained using firefly and particle swarm optimization (PSO) techniques. Improvement of Loadability margin is established through PV curve plotted using continuation power flow with the real power load at the most affected bus as the bifurcation parameter. The simulated output shows improved results when compared to that of firefly and PSO techniques, in term of convergence time, reduction of real power loss, improvement of voltage profile and enhancement of loadability margin.
文摘In a Power System, load is the most uncertain and extremely time varying unit. Hence it is important to determine the system’s supreme acceptable loadability limit called maximum loadability point to accommodate the sudden variation of load demand. Nowadays the enhancement of the maximum loadability point is essential to meet the rapid growth of load demand by improvising the system’s load utilization capacity. Flexible AC Transmission system devices (FACTS) with their speed and flexibility will play a key role in enhancing the controllability and power transfer capability of the system. Considering the theme of FACTS devices in the loadability limit enhancement, in this paper maximum loadability limit determination and its enhancement are prepared with the help of swarm intelligence based meta-heuristic Firefly Algorithm(FFA) by finding the optimal loading factor for each load and optimally placing the SVC (Shunt Compensation) and TCSC (Series Compensation) FACTS devices in the system. To illuminate the effectiveness of FACTS devices in the loadability enhancement, the line contingency scenario is also concerned in the study. The study of FACTS based maximum system load utilization acceptability point determination is demonstrated with the help of modified IEEE 30 bus, IEEE 57 Bus and IEEE 118 Bus test systems. The results of FACTS devices involvement in determining the maximum loading point enhance the load utilization point in normal state and also help to overcome the system violation in transmissionline contingency state. Also the firefly algorithm in determining the maximum loadability point provides better search capability with faster convergence rate compared to that of Particle swarm optimization (PSO) and Differential evolution algorithm.
基金International Medical University(IMU),Malaysia for financially supporting the present work under the research grant number BPharm B0108_Res322011.
文摘The aim of present study was to formulate and evaluate a self-microemulsifying drug delivery systems(SMEDDS)containing lovastatin and to further explore the ability of porous Neusilin■ US2 tablet as a solid carrier for SMEDDS.SMEDDS formulations of varying proportions of peceol,cremophor RH 40 and transcutol-P were selected and subjected to invitro evaluation,including dispersibility studies,droplet size,zeta potential measurement and release studies.The results indicated that the drug release profile of lovastatin from SMEDDS formulations was statistically significantly higher(p-value<0.05)than the plain lovastatin powder.Thermodynamic stability studies also confirmed the stability of the prepared SMEDDS formulations.The optimized formulation,which consists of 12% of peceol,44% of cremophor RH 40,and 44% of transcutol-P was loaded into directly compressed liquid loadable tablet of Neusilin■ US2 by simple adsorption method.In order to determine the ability of Neusilin®US2 as a suitable carrier pharmacodynamics study were also carried out in healthy diet induced hyperlipidemic rabbits.Animals were administered with both liquid SMEDDS and solid SMEDDS as well.From the results obtained,Neusilin■ was found to be a suitable carrier for SMEDDS and was equally effective in reducing the elevated lipid profile.In conclusion,liquid loadable tablet(LLT)is predicted to be a promising technique to deliver a liquid formulation in solid state.
