| In order to regulate the energy structure,while protecting the environment and rational use of energy,China will develop a clean renewable energy as an important strategy.In the renewable energy,wind power has its own advantages and occupies an important position in the energy market.It is also one of the most commercialized and industrialized of the developmental energy.In recent years,direct drive permanent magnet wind power generation system is developing very rapidly,and has been in hot pursuit of researchers.This is mainly due to its characteristics of direct drive,efficient and reliable.The traditional wind power generation system often use two level converter.But due to the problem of its high loss,high ripple current and low voltage-withstand ability,it restricts the further development of wind power.At present,with the rapid development of power electronics technology,the three level converter technology has been developed rapidly.The Neutral-Point-Clamped inverter is popular with researchers,because of its good voltage-withstand and the structure that without device series.Scholars put forward many methods in the control of three level converter.In recent years,the Space Vector Pulse Width Modulation is one of the mature control algorithm which is used commonly.This algorithm can improve the efficiency of power generation and the quality of power.This paper uses the full power converter to analyse the direct drive permanent magnet Neutral-Point-Clamped inverter of the SVPWM algorithm,puts forward a simple algorithm that is helpful for the neutral point voltage balance and then bases on the simulation platform to validate the analysis.This paper firstly introduces the background and significance of the research and summarizes the development trends of wind power basing on the statistical data in wind power generation.After being familiar with the theoretical knowledge and basic characteristics of wind turbine,the simulation model of wind turbine is established.This paper adopts the control method of climbing search method as maximum power point tracking,through the comparison of the basic principle and flow chart of three commonly hill-climbing search method to compare and analyze them.Then,to establish the mathematical model of wind power generation system and converter after knowing the basic structure and principle of permanent magnet synchronouswind power system of direct drive.The generator side adopts zero d axis current control strategy,the d axis current component is adjusted to 0,then can achieve the stator current control of electromagnetic torque.The network side uses the power grid voltage oriented control strategy.The control of active power and reactive power can be realized by adjusting the d,q axis current component respectively.This paper chooses SVPWM modulation algorithm as the full power converter modulation algorithm to achieve the further work and research.The study found a more simple way that by comparing of SPWM and SVPWM algorithm and put forward a kind of improved SVPWM algorithm.This paper analyzes and studies the factors that lead to the unbalance of neutral point potential.In the study of SVPWM algorithm,it introduces an adjustable neutral point balance coefficient K to control the fluctuation of the neutral point potential,by adjusting the range of k value.Finally,this paper uses the simulation software MATLAB / Simulink to build the simulation model of the wind power generation system and simulates the improved SVPWM modulation algorithm and the neutral point potential balancing control scheme.The simulation and experimental results verify the correctness and feasibility of the research ideas and the control algorithm. |
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