Abstract
Voltage stability improvement is a challenging issue in planning and security assessment of power systems. As modern systems are being operated under heavily stressed conditions with reduced stability margins, incorporation of voltage stability criteria in the operation of power systems began receiving great attention. This study presents a novel voltage stability constrained optimal power flow (VSC-OPF) approach based on static line voltage stability indices to simultaneously improve voltage stability and minimise power system losses under stressed and contingency conditions. The proposed methodology uses a voltage collapse proximity indicator (VCPI) to provide important information about the proximity of the system to voltage instability. The VCPI index is incorporated into the optimal power flow (OPF) formulation in two ways; first it can be added as a new voltage stability constraint in the OPF constraints, or used as a voltage stability objective function. The proposed approach has been evaluated on the standard IEEE 30-bus and 57-bus test systems under different cases and compared with two well proved VSC-OPF approaches based on the bus voltage indicator L - index and the minimum singular value. The simulation results are promising and demonstrate the effectiveness of the proposed VSC-OPF based on the line voltage stability index.
Highlights
During recent years, the planning and the operation of large interconnected power systems while improving system stability and security have become important concerns in the daily operation of modern power networks
(5) If the aim of the problem is the improvement of the overall voltage stability of the system and the minimisation of the power losses, the voltage collapse proximity indicator (VCPI) index is used as an objective function and the optimal power flow (OPF) is executed as follows:
The voltage stability constrained OPF based on the VCPI index for the stressed conditions results in a reduction of 38% in real power loss and 29.17% reduction in voltage stability index (VSI), but the generation fuel cost has increased by 11.3% which is acceptable considering voltage stability enhancement and power losses minimisation and the stressed conditions of the system
Summary
The planning and the operation of large interconnected power systems while improving system stability and security have become important concerns in the daily operation of modern power networks. An OPF for maximising voltage security through the use of the minimum singular value (MSV) of the power flow Jacobian was proposed in [18] and a voltage security constrained OPF based on the loading level parameter was formulated in [19] In these works, the authors tried to minimise the operating costs and the losses whereas maximising the distance to the voltage collapse. A VSC-OPF study has revealed that incorporating the VCPI index in the OPF is more efficient for voltage stability enhancement and power losses reduction. This work is focused on including the VCPI index in the classical OPF to effectively improve the voltage stability as well as minimise the power losses.
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