The Research On The High Power Inverter And Direct Current Connection Part For Offshore Wind Farm

In recent years, the world have been paying more attention to build the offshore wind farm. It is significant and urgent to research on the high power offshore wine farm converter which is the key part to connect the wind power with the grid.Compared with the ac inter-connection method, the dc inter-connection method that the power produced by wind turbine is rectified to dc and connected to dc bus is presented. The dc power is transmitted to land by dc bus and the power is connected with the grid by high power inverter and transformer. The research content is as follow:The low output voltage of uncontrolled rectifier bridge is raised up to 35 kV by the boost circuit and transmitted by the high voltage dc bus. We detect the output voltage of the rectifier and find the maximum power reference from a table. Then, we get the inductance current reference of the boost circuit which is used to control the duty cycle of the boost circuit and realize the maximum power point tracking.Based on the grid voltage vector orientation control strategy. We decouple for the three-level vector inverter and design the voltage loop and current loop. We also analyze the working principle of the three-level space vector pulse modulation, and put forward a control strategy basing on PI controller to solve the matter that the middle potential is unbalanced.We analyze the working principle of SSRF SPLL and DDSRF SPLL, and we simulate via SIMULINK. The simulation result shows that SSRF SPLL can work well when the grid voltage is balanced and DDSRF SPLL can work well no matter the grid voltage is balanced or unbalanced.Finally we simulate the system under four conditions via SIMULINK. The four condition includes ideal condition, the wind speed variation condition, the grid voltage unbalanced condition and the condition combined the wind speed variation with the grid voltage unbalance happened at the same time. The simulation result shows the system can keep stable quickly whatever for the situation. So the whole scheme is stable and reliable, it is satisfied for the high-power offshore wind farm.