Research On The Application Of The Dynamic Equivalence Of Power Systems

Large-scale power systems, regional interconnected power systems, AC/DC transmission systems are the development directions of China power grid. It’s difficult to simulate such a large-scale power grid, so it’s of great importance to simplify non-priority areas with the dynamic characteristics of the system unchanged. Dynamic equivalence not only can reduce Manpower and material resources but also ensure engineering accuracy, so it’s widely applied in many fields.With the development of HVDC transmission, Yindong DC transmission system merges into Shandong power grid. It’s the first±600kV project in the world and there is no operation data and experience before, so it’s necessary to study the influence between the AC system and DC system after the operation of Yindong DC system. Electromechanical transient simulation program and electromagnetic transient simulation program are two main kinds of tools to study the influence between AC and DC power system. For the dynamic characteristics of HVDC system is hardly to be studied while asymmetric faults occur in the AC system, it’s necessary to use electromagnetic transient simulation program. However, the scale of the simulated system is restricted by the algorithm of the electromagnetic transient simulation program; thus a dynamic equivalence method used in the electromagnetic transient simulation program should be employed.With the process of industrialization, the conventional energy resource is running out. Each country has to develop and use new energy and renewable energy. At present, wind power is the most promising one. Large-scale wind farms have significant influence on power system stability. Therefore, it’s of great significance to make a meticulous study on the transient characteristics of wind farms. If each unit is detailed modeled when researching the transient characteristics of large scale wind farms, not only workload is huge, models are complex, but also the necessary corrections for the models are needed, which is slow and arduous. Therefore, it’s necessary to find a suitable dynamic equivalence modeling method.The main tasks of this paper are as follows:l.A dynamic equivalence method based on physical equivalence is proposed.To study the dynamic characteristics of Yindong DC system, it’s necessary to simplify Shandong power grid. Coherent dynamic equivalence isn’t suitable for the electromagnetic transient simulation program. So a dynamic equivalence method suitable for the electromagnetic transient simulation program is proposed.The paper describes its principle and detailed steps. Equivalent model with the dynamic load is the innovation of this method. An equivalent is made of Shandong power grid based on PSASP. Compared the dynamic characteristics of equivalent models with that of the original system, the result shows that the equivalent effect is good.2.A dynamic equivalent modeling of wind farms with doubly-fed induction generator wind turbines under faults is proposed.Nowadays, doubly-fed induction generator (DFIG) is becoming the mainstream of wind power generation. Based on traditional equivalence modeling methods, the paper proposes a new dynamic equivalence modeling method. Equivalent model and the actual model of wind farms are built on the Matlab/Simulink simulation platform. Setting up different kinds of short-circuit faults, such as three-phase short-circuit, two-phase grounded and single-phase grounded, to power grid and compared the dynamic characteristics of equivalent model with that of the actual model, the result shows that the new method is more effective than traditional ones.In the end of this paper, a parameter identifying method based on PSO is proposed, which is used to calculate the parameters of equivalent models. The simulation result indicates that this method is more accurate than the weighting method, and it is more suitable for the complex working conditions wind farms modeling.