Control Algorithms For CSI In Direct-Drive Wind Power Generation System

Direct-drive wind power generation system is a form of newly-developed wind power generation system. This kind of system abandons the gearbox by using direct-drive generators, and hence gets a highly improved reliability. Direct-drive wind power generation system employs 100% capacity power converter to operate in parallel with the grid and satisfies the variable speed constant frequency working principle. The design of such power converter plays a key factor in guarantee the performance of direct-drive wind power generation system.The AC-DC-AC converter which comprises bridge rectifier and current source inverter (CSI) was studied as a topology for the 100% capacity power converter for the direct-drive wind power generation system. Both the circuit layer control principles and higher layer algorithms of system optimization were studied in this paper.Basic principles of determining the phase angle and amplitude value of CSI output current was put forward on the basis of analysis of the grid-connecting circuit. The method to control the CSI dc side voltage Vd c and the limits caused by the tansformation ratio of the grid-connected transformer on achievable Vd c range was studied. The conditions for the continuity of dc-link current id while Vd c varies was also systematically analyzed. An analytical method to derive the waveform of dc-link current id was detailedly investigated. By using this analytical method, the mechanical characteristic curves of the generator whose load is AC-DC-AC converter were derived in this paper.This paper also illustrated that the CSI dc side voltage Vd c has significant effects on the mechanical characteristic curve of the generator and Vd c can be used in the control of the operating point of wind power generation system. Novel MPPT algorithm based on Vd c disturbance was designed according to this fact and was tested through computer simulation in this paper.