symbolic solving Is there any limitations for maximum unknown for solve command

clc;

clear all;

format long;

Xm=3.5092;

Xr=3.5859;

Lm=Xm;

Lrr=Xr;

Rr=0.0088;

Rs=0.01015;

Xs=3.5547;

Xsp=Xs-(Xm*Xm/Xr);

Xlr=Xr-Xm;

Xls=Xs-Xm;

Wb=377;

R2=0.10;

X2=R2;

Tr=(Lrr/Rr);

R1=0.03;

X1=0.10;

XT=0.07;

Hd=2.0;

Ws=1.0;

KI=5;

KP=1;

syms Iqs Ids Vqr Vdr Idr Iqr wr Eqp Edp syms x4 x5 x6 x7 Ia Ib Vd Td VL Tl Pgen Qgen

R=15;

P=4;

K=1/45;

Vw=12.0;

Wre=wr*Wb;

Wrm=Wre/2;

OmegaTurbine=(K*Wrm);

Lamda=(OmegaTurbine*R)/Vw;

PitchTeta=0;

Co=3.239*10^-9;

Pref=Co*(wr*Wb)^3;

Qref=0.0;

PL=0.5;

QL=0.10;

Lamdai=((1/(Lamda+(0.08*PitchTeta)))-(0.035/(1+(PitchTeta^3))))^-1;

cp=0.22*((116/Lamdai)-(0.4*PitchTeta)-5)*exp(-12.5/Lamdai);

Pwind=(0.5*1.225*pi*R*R*(Vw^3));

Tm=(cp*Pwind)/(wr*(1*1000000));

term=(((Vqr*Iqr)+(Vdr*Idr))/Vd);

   % In 21 equations  there are 21  unknowns  

   F1=Wb*(((-1/Tr)*(Eqp +(Xs-Xsp)*Ids))+(((Lm/Lrr)*Vdr)-((Ws-wr)*Edp)));%  

   F2=Wb*(((-1/Tr)*(Edp -(Xs-Xsp)*Iqs))-(((Lm/Lrr)*Vqr)-((Ws-wr)*Eqp)));% 

    F3=(Wb/(2*Hd))*(Tm-((Eqp*Iqs)+(Edp*Ids)));

    F4=KI*(Pref-Pgen);

    F5= KI*((KP*(Pref-Pgen))+x4-Iqr);

    F6=KI*(Qref-Qgen);

    F7=KI*((KP*(Qref-Qgen))+x6-Idr);

    F8= -Vqr+(KP* ((KP*(Pref-Pgen))+x4-Iqr))+x5;

    F9=-Vdr+(KP* ((KP*(Qref-Qgen))+x6-Idr))+x7;

    F10=(-Pgen+((Edp*Ids)+(Eqp*Iqs)-(Rs*((Ids*Ids)+(Iqs*Iqs)))-((Vqr*Iqr)+(Vdr*Idr))));

    F11=-Qgen+((Eqp*Ids)-(Edp*Iqs)-(Xsp*((Ids*Ids)+(Iqs*Iqs))));

    F12=-Idr+(Eqp/Lm)+((Lm/Lrr)*Ids);

    F13=-Iqr-(Edp/Lm)+((Lm/Lrr)*Iqs);

    F14=Eqp-(Rs*Iqs)-(Xsp*Ids)-(Vd*cos(Td));

    F15=Edp-(Rs*Ids)+(Xsp*Iqs)+(Vd*sin(Td));

    F16=PL-((VL*cos(Tl))*(Ia+Iqs-(term*cos(Td))))-((VL*sin(Tl))*(Ib-Ids-(term*sin(Td))));

    F17=QL-((VL*sin(Tl))*(Ia+Iqs-(term*cos(Td))))+((VL*cos(Tl))*(Ib-Ids-(term*sin(Td))));

    F18=(Vd*cos(Td))-(R2*(Ia+Iqs-(term*cos(Td))))+(X2*(Ib-Ids-(term*sin(Td))))-(VL*cos(Tl));

    F19=(Vd*sin(Td))-(R2*(Ib-Ids-(term*sin(Td))))-(X2*(Ia+Iqs-(term*cos(Td))))-(VL*sin(Tl));

    F20=-1+(R1*Ia)-(Ib*(X1+XT))+(Vd*cos(Td));

    F21=(R1*Ib)+(Ia*(X1+XT))+(Vd*sin(Td));

disp('Going to solve symbolically');

S=solve(F1,F2,F3,F4,F5,F6,F7,F8,F9,F10,F11,F12,F13,F14,F15,F16,F17,F18,F19,F20,F21,...

Iqs,Ids,Iqr,Idr,Vqr,Vdr,wr,Eqp,Edp,...

x4,x5,x6,x7,Ia,Ib,Vd,Td,VL,Tl,Pgen,Qgen) % No proper order is required

S

Eqp=eval(S.Eqp)

Edp=eval(S.Edp)

wr=eval(S.wr)

x4=eval(S.x4)

x5=eval(S.x5)

x6=eval(S.x6)

x7=eval(S.x7)

Iqs=eval(S.Iqs)

Ids=eval(S.Ids)

Iqr=eval(S.Iqr)

Idr=eval(S.Idr)

Vqr=eval(S.Vqr)

Vdr=eval(S.Vdr)

Pgen=eval(S.Pgen)

Qgen=eval(S.Qgen)

Ia=eval(S.Ia)

Ib=eval(S.Ib)

VL=eval(S.VL)

Vd=eval(S.Vd)

TL=eval(S.TL)

Td=eval(S.Td)

I HAVE 21 EQUATIONS WITH 21 UNKNOWN,I am trying to solve it and get the solution using symbolic method But it is not getting solved but showing busy for more than hours.

Can anybody help in this to solve 21 unknowns with 21 equations.I worked till 15 unknown in 15 equations works well .Is there any limitations for symbolic solving and maximum number of unknown?