Research On Low Voltage Ride Through Of Direct-Driven Permanent Magnet Synchronous Generator

In recent years, wind power has undergone rapid development with its grid-connectedcapacity increasing constantly under the strong support of China. Meanwhile, the penetrationrate of wind power systems and grid is also rising. When the penetration rate is relatively high,once low voltage faults occur on the grid, the wind generator set will take off the grid sowidely that serious impact can take place on the safe grid operation. Low voltage ride through(LVRT) is the key technology by which the wind generator sets can be kept working on thegird and securities of the grid can be maintained when the low voltage malfunction takesplace. Hence, it is of great significance how to realize LVRT in the research.After analyzing the mainstream direct-driven permanent magnet wind generator set, thethesis chooses the back-back type direct-driven permanent magnet wind generator set as itsmain object for in-depth research. Initially, the principles and mathematical model of windturbine are analyzed, and then the simulation model is built and the computer simulation isfinished. Secondly, the generator side rectifier and grid side inverter are modeled in thedirect-driven permanent magnet wind power generation system. Based on above, the thesisfurther deduces the two side voltage equation expression. Thirdly, the thesis analyzes thecontrolling objects and controlling methods, and designs the controlling strategies of theconverter on both sides. Aiming at the difficult point in which the parameters of PI adjustorare designed when building simulation model, the theoretical analysis and calculation arecarried out, and PI adjustor’s controlling strategy and calculation methods are optimized withthe simulation made. Finally, a complete experimental simulation platform of thedirect-driven permanent magnet wind power generation system is built on the basis of theprevious results, and the low voltage simulation experiments and analysis is performedaccordingly.In order to realize LVRT, the addition of crowbar circuit is chosen at the DC side aftercomparing different LVRT strategies. At the same time, a new grid voltage detection methodis employed to examine the sudden drop rapidly in voltage. After the simulation experiment isperformed in MATLAB, the simulation results confirm that the LVRT can effectively solvethe low voltage problem of direct-driven permanent magnet wind power generation system，meanwhile, the feasibility and validity for the algorithm and the model are also verified.