Research On Multi-rate Simulation Method For AC-DC Power System Stability Analysis

Due to the development of modern power system, the multi-time scale characteristic of power system dynamics has become much more prominent than before, which has brought a great challenge to the power system simulation technique. This thesis focuses on multi-rate simulation method for AC-DC power system stability analysis, including three topics: modeling and simulation method for stability analysis of HVDC, the multi-rate simulation method based on self-adaptive grouping of variables, cross chain table based sparse matrix technique. The work is detailed as follow:HVDC models commonly used in stability simulation program, including simple model, response model and detailed model, are summarized. The applicability of the HVDC models for stability analysis is analyzed. The drawback of the AC-DC system two-time step simulation method for HVDC detailed model is discussed: the assumption of the AC commutating voltages being unchanged during the fast HVDC simulation may delay the action of some HVDC controls with switching characteristics, resulting in errors in simulation results. And it may even cause misoperation of the HVDC switching controls, which is the case in the study of multi-infeed HVDC system. A variable-step simulation method considering HVDC switching controls is proposed, which can make the HVDC switching controls act in time during the simulation. The proposed method can obtain a better accuracy than the conventional one, and the calculation efficiency is not eroded.A multi-rate simulation method based on self-adaptive grouping of variables is proposed for power system stability analysis. A high speed-up ratio is obtained by the self-adaptive grouping algorithm of variables, and there is no need to decide the grouping step ratio in advance which is the case in the conventional multi-rate simulation method. The very dishonest Newton (VDHN) method is adjusted for solving the grouped variables, including three steps: prediction, interpolation and correction. According to the characteristic of the VDHN method, a method for solving the grouped bus-voltage variables is presented which is a step of the correction process. Case study shows that the proposed multi-rate method can be well applied in both traditional large scale power system simulation and distributed generation system simulation.The structure and operation manner of cross chain table are presented to illustrate that its convenience and efficiency in serching, adding and deleting matrix elements can help speeding up the calculation process of factorization and forward-backward substitution. The impacts of the memory allocation manner of cross chain table on the calculation efficiency are discussed: nodes of cross chain table are always stored seperately in memory because of its memory allocation manner, which can reduce the calculation efficiency, and this phenomenon is caused by the principle of cache. To solve this problem, an improved cross chain table method is proposed. Case study proves the efficiency of the improved cross chain table, and shows that it can be well applied in both traditional large scale power system simulation and distributed generation system simulation.