how we can consider an "error" to control the reactive power in DFIG

Discussion in 'The Projects Forum' started by sara.ahmadi.27a@gmail.com, Mar 12, 2013.

  1. sara.ahmadi.27a@gmail.com

    Thread Starter New Member

    Feb 21, 2013
    10
    0
    hello every body
    in a wound rotor induction machine >>electromagnetic torque(Te) with neglecting of rotor and stator resistor losses is equal to:
    (1)Te=Ps/w1=Pr/wslip[1]
    {w1:angular speed of stator winding,wslip:angular speed of rotor winding,Ps=instantaneous power received from stator terminals ,Pr=instantaneous power delivered to rotor terminals}
    and

    (2)
    j.[d(wr)/dt]=Tmech+Te[1]
    {Tmech:mechanical torque,wr:rotor speed ,in generating, Te<0 ,Tmech>0,in generating, Te>0 ,Tmech<0}

    in field oriented control
    (3)Te=-3/2*p*Lm/Ls*flux_s_d*irq [2]

    {flux_s_d:stator flux (direct axis component),Lm:mutual inductance,Ls:stator inductance,p : pair pole,irq:current of rotor (quadrature axis component)}

    from (2) we can consider the "error of rotor speed from a reference speed"as electromagnetic torque,and then from(3) we can consider it as irq
    hence we can control the rotor speed with irq


    in that article[2]
    idr(direct component of rotor current) is considered to control the stator reactive power
    i don't know how we can consider an "error" to control the reactive power (similar to control the rotor speed with equation (2))?
    note that from another article[3] we have:
    (4)Qs=w1(flux_s_d/Ls)*(flux_s_d-Lm*ird)
    for the rotor side converter,articles [2],[3] are based on the synchronous reference frame fixed to the stator flux.

    Please discuss your opinions

    References:
    [1]variable speed generators(ION BOLDEA)
    [2]Doubly fed induction generator uising back-to-back PWM converters and its application to variablespeed wind-energy generation(R. Pena,J.C.Clare ,G. M. As her)(1996)
    [3]Coordinated reactive power control for facilitating fault ride through of doubly fed induction generator- and fixed speed induction generator-based wind farms(S. Foster, L. Xu, B. Fox)2008
     
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