Control of VSC-HVDC for wind farm integration based on adaptive backstepping method

Wind power is perhaps the most promising renewable energy for fossil fuel replacement in many countries. In order to integrate offshore wind farms, voltage source converter based high voltage direct current (VSC-HVDC) appears to be an appealing solution. Stable DC voltage is the key for successful power transmission, and this paper focuses on the advanced control method for stabilizing the DC cable voltage, aiming to achieve a stable power transmission. Based on the idea of adaptive backstepping control, DC cable is modelled as a series of π sections, and each section is responsible for the control of previous one. Inner current loop is then used to provide the final control signal of VSC and the global stability is guaranteed. Based on the voltage and current measurement, internal states of the DC cable can be estimated using a state observer. Using adaptive backstepping control, Matlab/Simulink simulations are carried out to demonstrate the effectiveness of the proposed method when active power changes. Compared with traditional PI control, it is shown that backstepping control can significantly improve the performance of existing DC voltage controller.