Research On Continuous Power Flow For PV Curve Based On PQ-QV Bus Switching

Today, with electric power increasing rapidly, power system gradually shows the feature of greater power, higher voltage and larger units. As power is delivered to load centers via high-voltage long transmission lines, the whole power system will under heavy load, or even worse, stability limit which can cause voltage instability or voltage collapse. To summarize, power system voltage stability problem is deserved to be paid high attention by power industry.As an effective method for power system voltage stability analysis, P-V curve based on natural power flow has two drawbacks:First, system flow equation is non-convergence when near inflection point or maximum power point of the system.. Second, when regional load power increases, simulate real change in the output of each generator can’t be simulated. And CPF as a solution to solve the problem above, one-dimensional is added in iteration matrix to avoid its convergence.Therefore, power flow algorithm based on PQ-QV bus type switching theory to draw P-V curve has been proposed.First, for calculation of P-V curve, the theory of eigenvalues, orthogonalization, singularity discrimination and spectral radius of matrix has been analyzed. Also continuation power flow and basic principles of sensitivity analysis has been discussed in detail, laying the foundation for proposing power flow algorithm based on PQ-QV bus type switching theory.Second, starting from the system voltage stability circuit model, voltage stability of two-bus power system has been analyzed. With WARD equivalence methodology, two-bus system standing for multi-bus system has been reducted and verified to put forward PQ-QV bus type switch theory, and balance equations of PV bus, PQ bus, QV bus in rectangular coordinates and polar coordinates has been built either.Third, sensitivity analysis in polar coordinates has proposed. To obtain Jacobi singular values, left or right singular vector, singular value decomposition of Jacobian matrix has been adopted. For better caculation of singularity in power system stability analysis, two algorithms have been brought up.The PQ-QV bus type switching theory bases on C language on MATLAB platform, and has been implemented with standard IEEE 9 bus system and IEEE 43 bus system. In addition, it has analyzed weak point and voltage stability margins of IEEE 43 bus system, for further use in practical systems.