Research On DPC Of Grid Side Converter Of Direct Drive Wind Power System Based On Duty Cycle Ratio Control

Abstract:wind speed randomness render power pulsation of direct power control strategy in direct drive wind power system much more serious compared with generation system of other new forms of new energy. This problem has a badly threat to security and stability of direct drive wind power system which has great necessity to be resolved. In order to resolve power pulsation and harmonic distortion caused by it of grid current of direct power control strategy in direct drive wind power system, direct power control based on duty cycle ratio is proposed.This paper analyzes grid-side converter’s operating principle and working status based on its circuit topology and simplified circuit, constructs mathematical model under three-phase stationary coordinate, two-phase stationary coordinate and two-phase synchronous rotating coordinate. According to the analysis of control demands of direct-drive wind power system, direct power control strategy is adopted aiming at control requirements of three control objectives in this paper.The mechanism of direct power control strategy is elaborated utilizing mathematical model and instantaneous power theory, two key steps including hysteresis comparators, voltage vector space partitions are discussed, a novel method of switching table designing is expounded mainly. The simulation results validates the effectiveness of direct power control based on new designed switching table, and indicated shortages of eliminating power pulsation and grid current harmonic distortion of direct power control in direct drive wind power system.To resolve the problem of power pulsation and grid current harmonic distortion of direct power control in direct drive wind power system better, found that power pulsation can be eliminated only by changing the duty cycle ratio of output voltage vector, direct power control based on duty cycle ratio is proposed, then the calculation expression of duty cycle ratio is derived according to the conditions for the elimination of power pulsation. In order to resolve the problem of the complexity of the relationship between the calculation expressions and circuit parameter, a method of the optimization of the calculation expression of duty cycle ratio is proposed, and the robustness and flexibility of strategy is improved further.The effectiveness and superiority of the direct power control strategy based duty cycle ration control and the method of the optimization of the calculation expression of duty cycle ratio by the results of simulation.