The Control Strategy Of Series-Parallel Topology DC Offshore Wind Farm Based On VSC-HVDC

Traditional offshore wind farm usually apply alternating collection type topology structure based on HVAC,as the offshore wind farm capacity increase,traditional transimission system and topology structure display disadvantages such as transmission capacity,high costs and so on.Therefore wind farm based on voltage source converter-high voltage direct current(VSC-HVDC),which was proved to be the best scheme will benefit offshore wind farm capacity expansion and long distance transmission.This paper studied the topology and configuration optimizations of series-parallel topology offshore wind farm based on voltage source converter-high voltage direct current,the paper also analysis operating characteristics of this kind of offshore wind farm.And then,starting from the calculation of wind energy,this paper study the characteristics of the wind turbine and the establishment of Direct-drive Permanent Magnet Synchronous Generator(D-PMSG),the mathematical model of PWM converter was studied too in this paper.The paper also investigates the operation characteristics of series-parallel Direct-drive Permanent Magnet Synchronous Generator(D-PMSG)wind farm based on voltage source converter-high voltage direct current(VSC-HVDC).For series-parallel topology wind farm,adopting traditional maximum power point tracking(MPPT)control strategy will lead to over voltage and overmodulation when the Wind turbines in same series branch under different wind speed.To deal with the problems,a novel control strategy of voltage-sharing is proposed for series-parallel topology D-PMSG based wind farm,which needs the super-capacitor energy storage system as hardware accessory equipment.By combining the running characteristics of series-parallel topology wind farm,the paper analysis and provides the design method of the super-capacitor capacity in detail.The proposed control strategy can limit each DC link voltage in voltage-sharing,which avoid the problem of over voltage and over-modulation when the system running in a special wind conditions.At last,the paper investigates the operation characteristics of series-parallel Direct-drive Permanent Magnet Synchronous Generator(D-PMSG)wind farm based on voltage source converter-high voltage direct current(VSC-HVDC),and a Power-voltage Coordination Control Strategy suitable for series and parallel topology MPPT is proposed.In addition,The upper limit of DC voltage is quantitatively alalyzed,which will ensure the system operates within a upper and low voltage limit in any operation states.The result of MATLAB/Simulink simulation proved the method can achieve the purpose of maximum wind power capture in a safe range.