Study Of Power System Load Model Based On The Perturbation Method

Stable operation of the power system is an important prerequisite for the healthy development of national economy and people’s normal life. With the increasing advances in science and technology, to meet people’s growing demand for power, the power system itself has undergone many changes, and all kinds of rationality of power system is becoming increasingly important.Power load is a more active part of the stable operation of the power system. The composite load modeling is an important issue for power system analysis, and reasonable load model is becoming the key of the credibility and accuracy of system simulation results. But load modeling is quit difficult for its characteristics of complexity and variability. Power system is a strongly nonlinear large-scale power system which consists of several important parts such as the generation, transmission, distribution, electricity, etc. The mathematical models of the system are also the strongly nonlinear differential algebraic equations, and the change rates of its physical quantities are quit different too. In order to reduce the difficulties of calculation and analysis brought by strongly nonlinear and rate differences, it is need to give up some minor factors to reduce the order of system model within the study, and the perturbation method avoid the blindness and irrationality of reduced-order. With the expansion of the grid-scale, the addition of the sensitive loads, the acceleration of the load growth and the aggravation of the load level, voltage instability incident is becoming a threat that must to be solved to the security of power system. In the first, this thesis introduces the necessity of the load model, discusses and compares two modeling methods, determines a more appropriate and more easily achieved method based on the research background conditions and the needs of this subject. Then it introduces the requirements of voltage stability to load models and the impacts of the load model on power system simulation, lists several common static and dynamic load mathematical models, and leads to the static characteristic coefficients and the dynamic load model which is adopted by this subject. While discussing the problem of voltage stability, the static load model has a big constraint for the study of power system dynamic characteristics. It is needed to both consider the static load and dynamic load, and the main component of dynamic load is induction motor load. At last, we value the static load and the induction motor load to a load with integrated structure by aggregation. This thesis analyzes several reduced-order approaches, and focuses on perturbation theory, its research status, and its associated research methods. Then it describes the mathematical basis of the multiple time scale method, and the original model and the reduced-order model based on the perturbation of induction motor load in detail is derived. This thesis presents the definition, research methods of voltage stability, analyzes and compares several static and dynamic analytical methods, and derives a mathematical model of the threshold voltage of the small signal stability in connection with the static characteristics of the induction motor. It elaborates the indicators of small disturbance voltage stability analysis and their response characteristics based on three models and the eigenvalue analysis method.The comprehensive model that through a series of analyzes simplifies the subsequent analysis process, and receives the data for this research. After the simulation, compare and analyze three models based on the actual examples, and verify the reasonable and timeliness of the perturbation model. All of these help to find a more suitable way to determine the component speed attribute, and would lay foundation for the more complex system model in future studies. The impact of the induction motor parameter changes to the small disturbance stability is given by using the practical examples. It is a useful reference for the further study of dynamic load modeling and prevention and correction to the system signal instability. And these verify the reference of the perturbation method is reasonable.