In[]:=
Vscc=1.5;f=0.6;τ1=Vscc;τ2=fVscc;τ3m=fVscc;m=20;PAI=0.04819277;λ=0.03150354;PSA=0.025;ni=IntegerPart[(m-τ1-τ2)/τ3m]+2;vti=Flatten[Append[{0,τ1,τ1+τ2},Table[τ1+τ2+(i-2)τ3m,{i,3,ni}]]];
In[]:=
fu[0,0]:=(PAI)/(PSA);fu[p_,t_]:=(1-Exp[-λ(t-vti[[p]])])+(PSAfu[p-1,vti[[p]]])-(1-Exp[-λ(t-vti[[p]])])(PSAfu[p-1,vti[[p]]]);
In[]:=
pwPA=Function[t,Piecewise[Partition[Riffle[Table[fu[p,t],{p,1,ni}],Table[vti[[i]]⩽t<vti[[i+1]],{i,1,ni}]],2]]];
In[]:=
pwPAMV=Function[u,Piecewise[{{pwPA[u-Vscc](PSA^(Count[vti,x_/;u-Vscc⩽x<u])),Vscc⩽u<2Vscc},{pwPA[u-fVscc](PSA^(Count[vti,x_/;u-fVscc⩽x<u])),2Vscc⩽u<vti[[-1]]}}]];Timing[pwPAMV[1.1]]Timing[pwPAMV[1.7]]Timing[Plot[pwPAMV[u],{u,0,1.7}]]
Out[]=
{0.,0}
Out[]=
{34.1094,0.00135427}