(From @ANJ) Matlab-Simulink integrator block already has the ability to integrate multidimensional signals without splitting them. input : Port_1 — Integrand signal : real scalar or array.
(From me) Link is updated http://airvigilante194.sdf.org/Scripts/deadbeatJeff.slx and humming along perfectly.
You can use the saturation block. Set the upper limit to "Inf" (thanks @Petrus1904) and the lower limit to 0.
The output of the saturation block should accordingly be only the positive values of whatever input you gave it.