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| Method | Features | Advantages | Limitations |
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| PV and QV curves [12] | They are plots denoting load bus voltage magnitudes for power increased in a particular PQ bus. The stability criterion is the “distance” between the current operating point and the extremes of these curves. | The curves give a quantitative measurement of the proximity to voltage collapse.
QV curves give the reactive power injection or absorption for various scheduled voltages, which is particularly useful when it comes to sizing of shunt capacitors.
The loadability limits of buses can be determined. | They are bus specific methods, and hence a large system would require a lot of computational effort.
Convergence problems tend to occur as loading on the system approaches the voltage collapse point; hence, it is not possible to know exact point of voltage collapse.
Fails to give useful information about the causes of voltage instability. |
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| Continuation power flow (CPF) [24, 25] | It is a technique used for tracing the whole of a PV curve by finding the next stable operating point for a given load or load change scenario. It utilizes the predictor-corrector method. | Provides a quantitative measure on the proximity to voltage collapse.
Overcomes convergence problems that arise with the use of PV and QV curves; hence, one can determine critical points of where voltage collapse occurs accurately. | Does not give information about the causes of voltage instability.
Bus specific, which makes it computationally intensive and time consuming. |
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| Singular value decomposition [26] | Utilizes the Jacobian matrix of a system where the determinant of the matrix is calculated for load increments until it reaches a minimum value. | Provides a relative proximity to the voltage stability limit | Does not provide information on the causes of voltage instability.
Does not give an absolute measure of the voltage collapse point. |
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| Sensitivity analysis [17] | Based on the sensitivity matrix derived from power flow equations. The sensitivity parameters are determined by the relationship between state variables and control variables. | Provides a good judge on the voltage stability status of a system.
Identifies voltage weak buses in a system. | The linear characteristics of the sensitivity index are not good especially for complex power systems; hence, it cannot accurately reflect the critical state of a system. |
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| Modal analysis [27] | It involves computing the smallest eigenvalues and associated eigenvectors of the reduced Jacobian matrix obtained from the power flow solution.
The eigenvalues and eigenvectors are used to calculate bus, branch, and generator participation factors which identify the cause of instability. | Gives information regarding the voltage stability status of a system from a system wide perspective both proximity to voltage collapse and mechanism of instability.
Identifies load regions most susceptible to voltage instability, weak buses and critical links in the network. | Eigenvalues do not provide an absolute measure of the proximity to voltage collapse. |
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