Full-process Hybrid Dynamic Simulation For Long-term Voltage Stability In Power Systems

Simulation analysis is the basic method to research long-term voltage stability of power system. Amoung existing simulation methods, full time-scale (FTS) simulation is most accurate, but the simulation speed is quite low because all components adopt detailed models. Quasi steady-state (QSS) simulation is quite fast but still too rough, for example, it can't distinguish transient voltage instability, and the judgement of discrete equipments' action time and order is not accurate enough, etc. Continuation-based quasi steady-state (CQSS) simulation can still maintain good convergence near the saddle-node bifurcation (SNB) point, but research shows that the trajectory of CQSS simulation gradually tends to departure and distortion after discrete equipments act in succession, so it still needs to be improved. Therefore, to develop an accurate and fast simulation method which is suitable for long-term voltage stability has quite important significance.Through combining FTS, QSS and CQSS simulation organicly, learning form their advantage and offsetting their disadvantage, and switching to each other appropriately, this dissertation represents a new simulation method for long-term voltage stability: full-process hybrid dynamic (FHD) simulation method. Detailed and quasi steady-state models of FHD simulation are discussed, and over-excitation limiter, armature current limiter and synthetic load are modeled. By comparing the simulation results of QSS and FTS simulation, it is discovered that system may not keep transient stability and enter long-term dynamic process afterwards when severe disturbances trigger discrete equipments to act in succession. Furthermore, judgment of discrete equipments through QSS simulation is inexact, which causes the system trajectory to depart from the real trajectory. On the other side, FHD simulation firstly adopts FTS simulation with detailed model after disturbances and discrete equipments' action, which keeps the system's electromechanical transient process, and overcomes the limitation that QSS simulation can't distinguish transient instability and the judgement of discrete equipments is inaccurate. When the system's electromechanical transient dies out, it switches to QSS simulation to accelerate the simulation speed. When the system approaches the SNB point, by the way of switching to the improved CQSS simulation, it can easily resolve the convergent problem caused by the singularity of Jacobi matrix with the precondition of not to reduce its accuracy. Therefore, FHD simulation is a fast simulation mechod with the precondition of guaranteeing accuracy, which is suitable for the simulation of long-term voltage stability.Finally, FTS simulation is taken as the criterion, the three simulation algorithm of FTS, QSS and FHD simulation are applied to the New England 10-machine 39-bus system and the IEEE 50-machine 145-bus system respectively. Through comparing analysis of the simulation results, the limitation of QSS simulation and the applicability of FHD simulation are proved.