Research On The Uninterrupted Grid-Incorporation Control Stratagem For The Direct-Drive Wind Power Generation System

Along with the enlargement of capability of wind turbine generator,the influence of wind power on the grid is more and more obvious.More and more high request is proposed by the grid company in the aspect of the characteristic of the low voltage ride through,the limitation of the active power and the power quality of the wind farm.Therefore,it is meaningful to do some research on the control of the converter,the low voltage ride through and smoothing of the active power for the safe,steady and high-efficient operation of the wind turbine generator.This paper makes a research for solving the above problem,the main research content is as follows:1?For problem of the zero sequence circulating current of the direct-drive wind power generation system which has paralleled two converters,the math model of the converters which has system parameter perturbation is derived.Due to the insensitivity of the sliding mode control to the system,whose parameter is uncertain,and its robustness,the controller of the zero sequence circulating current depending on the structure of sliding mode is designed.At the same time,the robustness of the control system is analyzed,and the integrator sliding mode which uses pole-placement is adjusted.The case analysis and simulation prove that the proposed control system can restrain the zero sequence circulating current and keep a good dynamic characteristic.2?This paper studies on the control strategy of direct-drive permanent magnet type wind turbine with symmetrical and asymmetrical grid voltage faults:when the grid voltage faults is symmetrical,the coordination control strategy of the generator-side and grid-side converter is proposed to realize the safe operation of wind turbine,provide reactive power support for grid and help grid returned to the normal state quickly;When the grid voltage faults is asymmetrical,the double current decoupling control in the synchronous rotating coordinates transform based on positive and negative sequences is proposed to realize the grid side converter constant active power control,at the same time,adopts the method of wind turbine accelerate,temporary store imbalance energy of power grid failure,stability the DC voltage;Realize the grid current control for grid-side converter without negative sequence.And the Super-capacitors energy storage system and the proportion-integration resonant controller is used to realize the tracking and compensation the difference value between the generator-side input power and grid-side output,and the ability of low voltage ride through is improved.3?Combined the fuzzy feedback control of the storage system state of charge and the pitch control,the wind energy capture reduces timely and appropriately,and the excess energy which the storage system cannot absorb is counteracted.The smoothing requirement is satisfied.The overcharge or over discharge of the storage system is avoided,and its life-time is extended.4?According to the regulations of wind connecting power fluctuations,the method of piece-wise smoothing is proposed.According to the characteristics of the wind farm typical output power curve,the appropriate smoothing time,and the energy storage capacity which meet all of request of the charge and discharge efficiency and state of charge is determined.On this basis,the wind power loss,interruptible load and storage system is considered to compensate the wind connecting power fluctuations.Under the premise of reaching the interconnection codes request,the annual total cost is much less than former system which only take the energy storage into account.When calculating the result,the improved cuckoo algorithm which has a better convergence speed and global search ability is proposed.The best state of charge,the output and capacity of the storage system is obtained.Output characteristics of wind farm cluster is modeled by the Gumbel Copula theory,then Latin hypercube sampling to obtain the temporal power curve,considering the power grid construction investment costs and benefits and loss of abandon the wind for transmission congestion,improve the utilization rate of the transmission line.5?Use time sequence production simulation method,considering the actual power system units of variety types and system constraints of many aspects,using mixed integer programming method,obtain largest wind power acceptable ability of each period and to get satisfactory effect.