Research On Frequency Integrated Control Strategy Of Directly-Driven Wind Turbine With Permanent Magnet Synchronous Generator

The directly-driven wind turbine with permanent magnet synchronous generator(DPMSG)adopts the maximum power point tracking(MPPT)control strategy.Its rotor speed is decoupled from the frequency of the power system.The increase of wind power penetration rate will threaten the stable operation of the power grid.Starting from improving the grid-connected frequency response characteristics of D-PMSG,this paper has completed the following work:Firstly,the mathematical model of each part of the D-PMSG is established.In order to focus the research on the frequency control strategy of wind turbines,the shafting model and the generator-converter model are simplified,and the overall simplified model of the wind turbine is established.Secondly,the structure of the additional inertia control is studied,and the mechanism of the additional inertia is analyzed.Aiming at the problem that it is difficult to set the proportional and differential coefficients of the additional inertial control,the proportional and differential coefficients were adjusted according to the equivalent synchronous generator set.Matlab/Simulink software was used to simulate the sudden increase and decrease in load analysis.Simulation results show that compared with the maximum power tracking control,the additional inertial control after parameter tuning can effectively reduce the system frequency drop speed and drop depth.Then,the principle of the pitch angle deloading frequency control strategy is analyzed.Aiming at the problem that it is difficult to determine the pitch angle and the load reduction level in the traditional pitch angle frequency control,a pitch angle deloading that changes the power set value is proposed.At the same time,the fuzzy PID controller is introduced to solve the problems of difficult tuning and poor adaptability of traditional PID controller parameters.Simulation results show that the proposed fuzzy PID-based control strategy for pitch angle deloading frequency can effectively achieve load reduction operation of wind turbines,provide long-term stable support for the system frequency,and change the final steady state value of the frequency.Finally,the advantages and disadvantages of additional inertia control and pitch angle deloading frequency control are compared and analyzed.A comprehensive control method combining the additional inertia and pitch angle deloading frequency control based on fuzzy PID is proposed.It can not only change the initial change rate and minimum value of the system frequency,but also change the steady state value of the system frequency.