Research On Power Balance Sliding Mode Control Strategy Of Direct-driven Permanent Magnet Wind Power System

With the resource crisis and environmental pollution continue to increase,people want to explore and use new energy more and more urgent,Wind power generation plays a very important role in the field of new energy because of its mature technology,low cost,safety and reliability.Permanent magnet direct drive wind power generation system has attracted great attention due to its advantages of high efficiency,reliable operation,simple control system.In this paper,the control strategies of power optimization and low voltage ride through of the permanent magnet direct drive wind power system is studies,based on sliding mode control.Firstly,the mathematical model of permanent magnet direct drive wind power system is studied.The aerodynamic model of the wind turbine model is started at a certain working point based on Talor expansion,Considering the changes of the fan working point and the external disturbances,a linear model of the wind turbine with uncertainties is obtained.Based on rotor flux orientation,The mathematical model of permanent magnet synchronous generator in dq coordinate system is obtained,And based on the grid voltage orientation,the mathematical model of the network side inverter in the dq coordinate system is obtained.Secondly,the maximum power point tracking based on fractional order sliding mode control of permanent magnet direct drive wind power system under rated wind speed is completed.A double closed loop control system with speed outer ring and current inner loop is adopted on the machine side,the motor follows the given optimal speed and outputs the maximum power,a double closed loop controller of the grid side controller is designed to stabilize the DC bus voltage and achieve the unit power factor into the grid.In order to verify the superiority of the designed controller,the designed controller is compared with the traditional PI controller.The simulation results show that the designed control strategy has fast response and high accuracy.when above the rated wind speed,in order to maintain the constant output power of the wind turbine,a nonsingular terminal sliding mode pitch controller and an adaptive sliding mode pitch controller are designed respectively.When the controller is designed,the influence of the uncertainty of model parameters and external disturbances are taken into account.In order to guarantee the stability of the controller,the parameter selection of the nonsingular terminal sliding mode control algorithm is often too conservative.While the parameters of the adaptive sliding mode pitch controller can be adjusted online,and the accurate identification of the model parameters is avoided.Simulation results show the effectiveness of the two control algorithms.Finally,the mechanism of low voltage ride through problem of D-PMSG wind power system is analysed and a new low voltage ride through control strategy is proposed without any additional circuitry.When the grid voltage drops,the DC bus voltage is stabilized by the machine side converter,and the reactive power is injected into the grid through the grid side converter to support the grid voltage recovery.At the same time,the pitch angel is forced to increase to reduce the unmatched power caused by the low voltage of the grid.In order to verify the superiority of the designed controller,the designed controller is compared with the traditional low voltage control strategy.The simulation result shows that under the proposed low voltage ride through control strategy,the impact is reduced to a certain extent and the low voltage ride through capability is improve a lot.