Nonlinear Coordinated Control Strategy Research Of Direct-Drive Permanent Magnet Wind Power System

Direct-drive permanent magnet wind power system has been attracted widespread attention in recent years based on its high energy conversion rate, reliability, flexible, and many other advantages. Ensure the system operates on different wind speed stably and its grid-connected control strategy has become a hotspot in research of wind power generation technology. This paper based on the modeling of a direct-drive permanent magnet wind power system, have proposed a multi-objective nonlinear coordinated control strategy to satisfy requirements of the whole system running and grid-connected control. This control strategy has certain benefits on theoretical research and engineering practice. Paper’s main work is as follows:(1) The nonlinear mathematical model is established by analysis the working principle of the wind turbine, the loss model of permanent magnet synchronous generator, the double PWM rectifier inverter device and the pitch-controlled system,(2) For a direct-drive permanent magnet wind power system under rated wind speed of maximum wind energy capture control requirements, six order nonlinear differential equations are established. The multi-objective coordinated control strategy of the system can obtain by the part accurate linearization control theory. The strategy has achieved the maximum wind energy capture goal on the generator side, and make sure the generator loss is minimum. At the same time, the strategy stables the DC bus voltage and regulates reactive current on the grid side, and ensures the system under normal condition of unit power factor grid-connection. When the grid voltage drops suddenly, the system can quickly provide reactive current, support the grid recovery. The simulation results verify the correctness and effectiveness of this strategy. (3) When the wind speed exceeds the rated wind speed, wind power system operation requirements become constant power control. Taking the pitch-controlled system of direct-drive permanent magnet into account, seven order nonlinear differential equations of wind power system are established. Based on multi-objective feedback linearization coordinated control strategy, we select five output functions. On generator side, the coordinated control of generator speed and output power improve the performance of the constant power control, and the grid side satisfy the requirement of system connect the grid. The control strategy has the capability of low voltage ride-through. The time domain simulation shows that this control strategy is effective.