Research On Power Control Technology Of Grid Side Of Permanent Magnet Wind Turbine Generator

The output power of the traditional permanent magnet wind turbine network side is usually operated by a given power factor or stratified joint regulation.And some need to be equipped with a reactive power compensator to maintain the stable operation of the power system,additionally increase the cost of electricity for the user.There is less consider about the reactive power response for the single machine.With the large-scale application of wind power generation,the demand for improving the high voltage and low voltage fault ride-through capability of wind turbines has increasing.The main work of this thesis on the above issues is as follows:1)In view of the weak reactive power response capability of wind turbines,the working principle and topological structure of wind turbines are studied,and the mathematical model of grid-side converter of wind turbines is established.A dynamic reactive power compensation method based on direct reactive current control is designed to realize information exchange between grid-side converter and reactive power detection module,and dynamic reactive power compensation for load is completed within the constraint of output current of grid-side converter.The dynamics of the load are completed within the constraints of the grid-side converter output current.The power compensation,by observing the phase-phase operation of the phase A voltage and current of the grid,shows that the reactive power is compensated in real time,which proves that the wind turbine can complete the dynamic reactive power compensation while outputting the active power.2)The operation characteristics of grid-side converters and DC buses of permanent magnet wind turbines are studied when grid voltage drops.The mechanism of voltage instability of DC buses is analyzed,and the maximum power output method of permanent magnet wind turbine based on unloading circuit is designed.The control block diagram of the grid-side converter and the logic relationship with the master control are given.The DC bus voltage is controlled by the unloading circuit when the output power is limited,and the grid-side converter outputs at the maximum current;During the remaining capacity,the DC voltage is switched to the voltage outer loop control,and the additional power is added to promote the grid voltage recovery,further enhancing the low voltage ride through capability of the permanent magnet wind turbine.3)In view of the high voltage ride-through problem of PMSG,based the traditional wind turbine vector control,a high voltage ride through method about automatic control DC voltage and dynamic reactive power control has been proposed.The influence of DC bus voltage and reactive power on the amplitude of equivalent output voltage of the grid-side converter during normal operation and high voltage fault has been analyzed.The relationship between the output power of the grid-side converter and the line impedance for the voltage amplitude of the wind turbine’s grid-connected point has also studied.The control block diagram of the permanent magnet wind turbine converter during high voltage crossing and the coordinated control mechanism with the main control system are given.Through the joint control of DC voltage and reactive power,the maximum equivalent output voltage of the grid-side converter is increased while the voltage of the grid-connected point is reduced.This method also avoid uncontrolled increase of DC voltage,and reducing the fluctuations of output active power.Finally,the dynamic reactive power compensation,low voltage ride through and high voltage ride through method of the permanent magnet wind turbine are simulated and analyzed.The effectiveness of the proposed method is verified.