此类型的变量不支持使用点进行索引怎么解决

%三变压器53节点系统，SOP看为一个节点，系统基准容量维1MVA,基准电压11KV ，利用矩阵构造网络  定义一个Pg,Pbi,Psi
%均用Pg中元素表示，然后再增添约束
clear all; clc;
warning off;
tic
%% 1.初始数据
%基本参数
mpc=IEEE53;
Pload=mpc.load(:,1);  %有功负荷 KVA
Qload=mpc.load(:,2);  %无功负荷 Kvar
branch=mpc.branch;
r=branch(:,3);  %线路电阻 Ω
x=branch(:,4);  %线路电抗 S
Poz = [2.72;3.2;3.8];  %变压器空载损耗 KW
Pkz = [19.35;20.7;24.3]; 
Sei = [2000;2500;3150];  %变压器容量 KVA
Ssop=3000;  %SOP容量 KVA
nb=53;
nl=52;
Vmax=[1.1*1.1*ones(26,1);1.1;1.1*1.1*ones(15,1);1.1;1.1*1.1*ones(9,1);1.1];  %节点27、43、53电压固定
Vmin=[0.9*0.9*ones(26,1);1.1;0.9*0.9*ones(15,1);1.1;0.9*0.9*ones(9,1);1.1];

upstream=zeros(nb,nl);
dnstream=zeros(nb,nl);
for i=1:nl
    upstream(i,i)=1;
end
for i=[1 3 4 5 8 10 12 13 15 16 18 19 22:26 30 31 33 36 38:42 44 46 49]
    dnstream(i,i+1)=1;
end
    dnstream(1,3)=1;
    dnstream(3,8)=1;
    dnstream(5,7)=1;
    dnstream(8,10)=1;
    dnstream(10,12)=1;
    dnstream(11,22)=1;
    dnstream(13,15)=1;
    dnstream(16,18)=1;
    dnstream(19,21)=1;
    
    dnstream(22,38)=1;
    
    dnstream(24,28)=1;
    dnstream(24,29)=1;
    dnstream(25,30)=1;
    dnstream(26,36)=1;
    dnstream(26,33)=1;
    dnstream(33,35)=1;
 
    dnstream(41,49)=1;
    dnstream(42,44)=1;
    dnstream(42,46)=1;
    dnstream(46,48)=1;
    dnstream(49,51)=1;
    dnstream(49,52)=1;
    dnstream(53,1)=1;
    
   
%% 2.设决策变量
P=sdpvar(nl,1,'full'); %节点流出功率
Q=sdpvar(nl,1,'full');
I=sdpvar(nl,1,'full');
V=sdpvar(nb,1,'full');
Pg=sdpvar(nb,1,'full');
Qg=sdpvar(nb,1,'full');
Pbi=[Pg(27);Pg(43);Pg(53)];
Qbi=[Qg(27);Qg(43);Qg(53)];
Psi=[-P(22);P(23);P(38)];
Qsi=[-Q(22);Q(23);Q(38)];

%% 3.约束
C=[];
 %% 潮流约束
 %节点功率平衡约束
Pin = -upstream*P + upstream*(I.*r) + dnstream*P;  %节点注入有功
Qin = -upstream*Q + upstream*(I.*x) + dnstream*Q;  %节点注入无功
C=[C,Pin+Pload-Pg == 0];
C=[C,Qin+Qload-Qg == 0]; 
%欧姆定律约束
C = [C, V(branch(:,2)) == V(branch(:,1)) - 2*r.*P - 2*x.*Q + (r.^2+x.^2).*I];
%二阶锥约束
C = [C, V(branch(:,1)).*I >= P.^2 + Q.^2];

 %% 通用约束
%节点电压约束
C = [C, Vmin <= V,V <= Vmax];
%支路电流约束
C = [C, 0 <= I,I <= 0.11];
%支路功率约束
C = [C, -0.11<=P,P <= 0.11,-0.11 <= Q,Q <= 0.11];

%% 器件约束
%SOP容量约束
% C=[C,Psi(1) == -P(22);Psi(2)==P(23);Psi(3)==P(38)];  %SOP有功功率
% C=[C,Qsi(1) == -Q(22);Qsi(2)==Q(23);Qsi(3)==Q(38)];%SOP无功功率

C=[C,sqrt(Psi.^2+Qsi.^2)<=3000];
%变压器容量约束
%C=[C,Pbi==[Pg(27);Pg(43);Pg(53)];Qbi==[Qg(27);Qg(43);Qg(53)]];
C=[C,sqrt(Pbi.^2+Qbi.^2)<=Sei];
%变压器最佳经济运行区间约束
belta2 =(Pbi.^2+Qbi.^2)./(Sei.^2);
C=[C,0.0625<=belta2,belta2<=0.5625];
%% 4.目标函数
%变压器综合损耗
Pzi=sum(Poz+belta2.*Pkz);
%SOP端口传输损耗
Psi_loss=sum(0.02*sqrt(Psi.^2+Qsi.^2));
%线路损耗
Ploss=sum(I.*r);
%总损耗
objective=Pzi+Psi_loss+Ploss;
toc %建模时间
%% 5.设置求解器求解
ops=sdpsettings('verbose',1,'solver','cplex');
% ops.fmincon.MaxIter=100000;
% ops.fmincon.MaxFunEvals=1000000;
sol=optimize(C,objective,ops);
toc%求解时间
%% 6.分析错误标志
if sol.problem == 0
    disp('succcessful solved');
else
    disp('error');
    yalmiperror(sol.problem)
end

是一个电力系统优化方面的问题，实在不知道怎么解决了，碰到过好多次了每次卡在这里