Research On Control Method Of Cascade STATCOM In Grid-connected Of Large Scale Wind Power

With the large-scale wind farms put into use, the grid power qualityproblem is becoming increasingly serious by it. By equip reactive powercompensation device to the wind farm exports to realize dynamicallycompensated the reactive power grid system and stable the access pointvoltage, improving the low voltage and fault crossing ability of windturbines, reducing the impact of large-scale wind power grid to power grid.This article made a more in-depth research aims to the control method ofcascade STATCOM device intermediate in wind farm.First, introduced commonly used main circuit topology of the highvoltage and large capacity STATCOM system, compared the advantagesand the disadvantages of them, pointed out that the advantage of cascadetopology. Analysis of the principle of cascade STATCOM based on thevector diagram, designed the main circuit parameters of it, Nature ofmonopole harmonics SPWM modulation strategy is deduced in detail andexplains its advantages.Then, in view of the DC side capacitor voltage imbalance of cascadeSTATCOM, proposed a method of active power equal allocation modulecontrol according to the DC voltage balance, by adjusting the size of theactive power of the ac absorption to control the size of the DC side voltage,cascade STATCOM using layered coordination control of active andreactive power control, The upper used decoupling to achieve overallcontrol, the lower used active power equal distribution control to achievethe module control. Simulation and experimental results show that thismethod is effective to solve the key problems which DC side capacitorvoltage is difficult to balance of the cascade STATCOM.Third, In view of the unbalanced condition of the lower leagueSTATCOM control problem, put forward the output equivalent negativesequence voltage method to ensure that the access point voltage balance ofcascade STATCOM. Analysis the operating characteristics underunbalanced conditions, System was deduced in detail in the positivesequence and negative sequence under the environment of decouplingcontrol equation; put forward the positive sequence-negative sequence decoupling control method of PWM, analysis of the extension of the twokinds of working mode: Reactive power compensation and voltage control.According to the three range of imbalance, Period of time control system isput forward, implements the maximum use of the plant. Simulation andexperimental results show that this method is effective to ensure safe andstable operation of the cascade STATCOM under unbalanced conditions.At last, designed the software and hardware based on control system ofthe cascade STATCOM, Hardware platform is based on doubleDSP+FPGA+CPLD combination system, designed respectively on themain control board and the power unit control system hardware. Usingflow chart to design the control software, Mainly includes DSP1and DSP2main program and interrupt program control, PWM signal generation andthe monitoring software design.