% m-file for calculating on load tap changing計算有載分接頭的變化.
%        要求使LT母線電壓保持在電壓極限內，這時假定HT母線電壓不變。
%        檢查LT母線電壓幅值，如果超出極限，計算電壓和極限之間的偏差，
%        改變分抽頭減小偏差，如果達到分抽頭的極限還不能使電壓正常，提示錯誤。
% called by Loadflow被loadflow調用
% calculates desired tap assuming HT(from bus) voltage fixed假定高壓端電壓（初始節點）固定
% and the to bus voltage is set to the voltage limit另一端節點設置為電壓極限
% the tap is set to an allowable tap seting分接頭設置允許范圍
% and the line matrix tap setting entry is changed線路矩陣的分接頭設置改變
% if all voltages are within limits the loadflow is taken as
% converged如果所有的電壓都在范圍內，潮流就收斂
%
%Author  Graham Rogers
%Date    October 1996   

max_v_idx = find(V>=volt_max);%找出電壓大于等于最大電壓限制的
min_v_idx = find(V<=volt_min);%找出電壓小于等于最小電壓限制的
mm_chk = 0;
if (~isempty(max_v_idx)|~isempty(min_v_idx))%如果找到表示或的關系
   mm_chk = 1;
   if ~isempty(max_v_idx)%如果找到大于等于電壓極限的
      % change on load taps to correct voltage改變分接頭使電壓正常
      % assumes that bus to be corrected is the to bus 假定末端節點被修正？
      for fb = 1 : length(max_v_idx)%循環次數等于電壓越界的節點個數
         chk_fb = find(line(:,2) == bus(max_v_idx(fb),1));% 第n次循環是:找到越界電壓所在的支路位置
         if ~isempty(chk_fb)%如果有
            % freeze dc taps凍結直流節點分抽頭？
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5           
            if ~isempty(n_dcl)%*************************************************?？？？在loadflow中定義了global,直流抽頭調節
               for kt = 1:2*n_dcl 
                  dc_chk = find(chk_fb==ac_line(kt));
                  if ~isempty(dc_chk);chk_fb(dc_chk)=[];end
               end
            end
         end
         
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%       
         if ~isempty(chk_fb) %如果找到非空
            if line(chk_fb,8)~=0       %第8列是最大分接頭，給出了最大分接頭，最大調節為非零，還有最小分接頭
               % can change tap可以改變分接頭
               % get from bus voltage
               disp('voltage high changing tap on line');disp(chk_fb)
               vm2 = volt_max(max_v_idx(fb));%這個節點的最大額定電壓volt_max是一個全局變量
               verror = V(max_v_idx(fb))-vm2;%實際電壓-上界＝電壓差
               % voltage too high, tap must be increased
               %電壓太高，分抽頭必須增大。高壓端電壓確定，變比與低壓端電壓成反比
               if verror/vm2 < line(chk_fb,10)%電壓差/最大額定電壓 < 這個節點分接頭的等級
                  % increase tap by one step一級一級的增加，比一級略小
                  tap = line(chk_fb,6) + line(chk_fb,10);%變比＝原來的變比 + 一個等級：增加一級
               else%如果電壓差/最大額定電壓>＝一個等級
                  tap = line(chk_fb,6) + verror/vm2;%分接頭＝原來的＋電壓差/最大額定電壓
                  tap_set = ceil( (tap-line(chk_fb,9))/line(chk_fb,10));%第幾級＝（分接頭－最小分接頭）/分接頭等級
                  %         ceil（x）是取最接近x的整數
                  tap = tap_set*line(chk_fb,10) + line(chk_fb,9);%tap=最小的分接頭＋等級*第幾級
               end
               %  選擇了最接近的分接頭
               tap = min(line(chk_fb,8),max(tap, line(chk_fb,9)));%*******************選擇一個最大分接頭與所選則分接頭中最小的一個
               % reset tap in line data重置線路數據中的分接頭
               disp('tap reset to');tap
               line(chk_fb,6) = tap;
            end
         end
      end
   end 
   if ~isempty(min_v_idx)%如果有電壓超過下界的。同上
      % change on load taps to correct voltage
      % assumes that bus to be corrected is the to bus
      for fb = 1 : length(min_v_idx)
         chk_fb = find(line(:,2) == bus(min_v_idx(fb),1));
         if ~isempty(chk_fb)
            % freeze dc taps
            if ~isempty(n_dcl)
               for kt = 1:2*n_dcl 
                  dc_chk = find(chk_fb==ac_line(kt));
                  if ~isempty(dc_chk);chk_fb(dc_chk)=[];end
               end
            end
         end
         
         if ~isempty(chk_fb)
            if line(chk_fb,8)~=0
               % can change tap
               disp('voltage low changing tap on line');disp(chk_fb)
               vm2 = volt_min(min_v_idx(fb));
               verror = vm2 - V(min_v_idx(fb));
               % voltage too low tap must be reduced
               if verror/vm2<line(chk_fb,10)
                  % reduce tap by one increment
                  tap = line(chk_fb,6)-line(chk_fb,10);
               else
                  tap = line(chk_fb,6) - verror./vm2;
                  tap_set = fix( (tap-line(chk_fb,9))/line(chk_fb,10));
                  tap = tap_set*line(chk_fb,10) + line(chk_fb,9);
               end
               tap = min(line(chk_fb,8),max(tap, line(chk_fb,9)));%？
               disp('taps reset to');tap
               % reset tap in line data
               line(chk_fb,6) = tap;
            end
         end
      end
   end
end