Grid-side Converter Technology And Control Parameter Optimization For Permanent Magnet Wind Turbines

The current development trend of offshore wind turbine is the single capacity large-scale,variable current unit modular.With the yearly increase of single-machine capacity,it is difficult to achieve the output requirements of traditional two-level shunt topology due to the cumbersome structure and control.In contrast,medium-voltage three-level shunt system with high voltage withstand level,strong transmission efficiency and simple control strategy has become the best choice for offshore wind power.However,there are relatively few researches on grid-side converter technology corresponding to high-power systems.Therefore,based on the research on the topology of high-power offshore permanent magnet wind turbines,this thesis discusses the phase-locking,filtering in the grid-side converter system.And the corresponding model control parameter optimization technology to carry out related work.First,by comparing the advantages and disadvantages of various three-level converters and wind power system structures,the topology of "multi-phase motor + distributed three-level converter" is selected as the research object.based on which the mathematical model of wind turbine,six-phase permanent magnet motor and Neutral Point Clamped（NPC）three-level converter is established.and the maximum torque control strategy is studied to assume the output energy on the machine side.Secondly,the equivalent circuit and dynamic commutation principle of the NPC threelevel converter system are analyzed,unit specifications of the adapter components are selected by calculation,and the virtual vector modulation method,which combines the medium and small vectors proportionally into a virtual mid-vector to dynamically maintain the potential,is studied for the mid-point potential imbalance caused by the unique topology of the three-level converter,and the effect of this modulation method is verified by simulation.Then,in order to adapt to high-power wind turbines,redesign some units on the corresponding grid side.One: to realize the phase-locked loop to extract the grid voltage frequency to maintain the grid synchronization with the converter,an improved generalized integrator with add notch filter is designed to improve its anti-disturbance,and to capture the grid frequency and phase under both grid normal and fault.The second is to establish the LLCL filter model in combination with the design constraints.Since the filter unit is the interactive interface between the converter system and the power grid,it is necessary to study the LLCL unit after setting parameters.on the bad ripple in the current signal at the switching frequency and the integer frequency after PMW modulation of the converter.In the grid-side control,a simple voltage-oriented vector control strategy is adopted,and the closed-loop system controller parameters are determined by the classical method to supply energy to the grid.The effectiveness of each unit on the grid side is verified by simulation software.Finally,to improve the wind turbines control performance,the Particle Swarm Optimization（PSO）algorithm is used for the variable flow control system with strong nonlinearity.In view of its shortcomings of slow convergence and easy to fall into local optimum,the design introduces random weights and self-mutating hybrid particle swarm method（Hybird PSO,HPSO）,optimizes the PI parameters designed by the machine/grid-side controller under the traditional tuning method with the expectation of overshoot and stabilization time.The traditional parameter design method is compared with the signal derived by HPSO optimization under two conditions of variable wind speed and jump grid-side DC source.The simulation output shows that after the model control parameters are optimized by HPSO,the dynamic and static responsiveness and stability of the converter system are improved.