Research On DC Bus Voltage Control Strategy Of Grid-side Converter In Direct-drive Wind Power System

In the present society,with the growing energy crisis,wind power is widely used due to its cleanliness,renewable nature,good environmental benefits,short infrastructure cycle and flexible installation scale.In order to meet the grid-connected power quality requirements of the power grid,the grid-connected inverter of the wind power system must be controlled.Direct-drive wind power systems are more efficient and reliable than doubly-fed systems.Therefore,the control strategy of the grid-side inverter of direct-drive wind power systems is investigated in this thesis.The main research is carried out as follows:1)Firstly,the thesis starts from the development of wind power energy,the current situation of wind power development at home and abroad as well as the classification of inverters and the development of control technology,describes the general structure of wind power systems,the working principle of grid-connected inverters and their mathematical models,and analyses the grid-connected inverter its PI control strategy based on grid voltage directed double closed-loop control and the method of parameter rectification in the dq coordinate system.2)The second-order LADRC controller is designed to replace the PI controller in the voltage outer loop of the traditional double-closed-loop structure,for solving the problems of overshoot and rapidity that cannot be solved by the PI controller.Finally,the simulation model of the 1.5 MW direct-drive wind power grid-connected system is built by the MATLAB/Simulink digital simulation software,and the designed LADRC controller is verified by simulation.3)To address the problem of insufficient immunity and tracking caused by the difficulty of parameter rectification,fuzzy theory is introduced in the thesis to modify the LADRC controller,which on the one hand enables it to achieve automatic optimization of parameters in complex operating conditions and greatly improves the transient process of the system;on the other hand,the robustness of the grid-connected controller is improved.4)With the help of the hardware-in-loop simulation,a 3.6 MW wind turbine simulation was carried out to simulate the fault ride-through capability of the DC bus voltage under grid voltage balanced or unbalanced high voltage ride-through(HVRT)and low voltage ride-through(LVRT).The experimental results validate the effectiveness and feasibility of the control strategy proposed in the thesis.