Research On Impact And Countermeasures Of Grid Voltage Sag On Low Voltage Ride Through Of Wind Power System

With the "Twelfth Five-Year Plan" developing wind energy rapidly, Chinese wind power continues to make progress in our main. The proportion of wind power is more and more important in the power system, so the impact between wind power and grid cannot be ignored. When the grid voltage sag occurs, the wind power generation system should be continue operating in order to prevent wind power system from off-grid and avoid a tremendous impact on the power grid, which requires that the wind power system must process low voltage ride through capability.In this paper, we do some relative study based on the permanent magnet direct drive wind power generation system:1 Permanent-magnet direct-drive wind power system and its mathematical model is researched, the corresponding control strategy of generator side and line-side is put forward, and achieve decoupling control of active and reactive power on both sides of the inverter.2. DC-link of converter and grid side converter is studied for in-depth in case of power grid failure status. Under single-phase to ground fault and three-phase grounding fault occurring, the dynamic characteristics of grid side converter and its DC bus voltage is analyzed. When the grid fails, machine side converter and power grid side converter occur input and output imbalance, which lead the DC-link and grid side taking place converter over-voltage and over-current hazard reasons. Both of voltage sags caused by fault type and voltage sag depth are studied. A fault type criteria is proposed, which is based on combination of phase voltage and zero sequence components. The module is established in PSCAD/EMTDC to verify the correctness of research and analysis.3. A program is put forward by using dynamic voltage Restorer to achieve low voltage ride through. Zero active power compensation system with reactive support is to improve the voltage stability, enhance the LVRT. Adding inverter DC Energy dissipation circuit is to improve the ability of DC bus voltage across the resistance. Low voltage ride through models of direct-drive wind power system is built in the PSCAD/EMTDC. Simulation results show that the program is correct.