| In recent years, wind power generation system has gained rapid development worldwide, and the grid operators in many countries have put forward higher request for wind power penetration capability, such as LVRT (low voltage ride through), reactive power (voltage) control ability, active power (frequency) regulation ability and so on. The prediction and simulation of large-scale wind power access to the power system has become the focus of attention. With the deepening of the research on wind power grid technology, wind turbine model requires more accuracy, reliability and reasonability. Actually, the lack of accurate model has affected the research on wind power grid system, which makes the accurate evaluation of the influence of wind power access to power grid difficult to achieve. So, it has important practical significance to study the LVRT control strategy and the electromechanical transient model that conform to the actual wind turbine.At present, tracking research progress abroad, domestic commonly used power system analysis software usually simulates with a certain type when analyzing the electromechanical transient model of the widely used doubly-fed induction generator (DFIG) and the permanent magnet synchronous generator (PMSG). As a matter of fact, the wind turbine model research abroad is also refined and perfected towards mainstream manufacturers. For a long time, domestic manufacturers have introduced existing equipment from abroad, thus, being weak in modeling and parameter technology. Through cooperation with wind turbine manufacturers and combining with electromechanical program, great progress is expected in modifying and refining the model.Taking DFIG and PMSG as the research object, this paper mainly focuses on the theory research on the mathematical model and the LVRT strategy and the main contributions are as follows:Firstly, the mathematical model of DFIG and PMSG is studied, including the wind turbine model, the generator model under synchronous dq coordinates, the converter model and so on. Then, the control strategies of each part of the two wind power generation systems and the motor speed control method under the condition of the steady state are studied. The correctness of the above research is validated in DIgSILENT and PSCAD through building the electromechanical model.Secondly, the fault features of DFIG and PMSG is analyzed from the perspective of energy balance and simulation validates the effectiveness of LVRT strategy using lever resistance under symmetrical fault and asymmetrical fault. The qualitative analysis of the impact of the lever resistance on LVRT effect and discussion of the selection principle of the limiting resistor are also included in this paper.Thirdly, on the basis of in-depth study of the electromechanical model of DFIG and PMSG, the electromechanical model in PSASP is developed according to different factory in Shandong province, which can be used for transient stability analysis of large-scale wind farms connected to the power system. The effectiveness of the model is validated through comparing the simulation results and the actual low voltage ride curve. Thus, it can be used for the simulation calculation for each manufacturer. The reliability and accuracy is verified by a lot of simulation results. At last, this paper studies the equivalent method of the wind farm using one or several wind power generators, including the equivalent of wind power generators, generator transformers and centralized sections. The equivalent method is used to study the wind power generator and LVRT characteristic and the ability of large-scale wind power access to the power system can be predicted and simulated. |
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