PULSEGEN For a Binary Output-But-Modulating-Actuator

We have a binary output but modulating actuator (valve and motor) that is to be used to control some process variable (e.g., flow). That is, the motor/valve has can be commanded by two digital outputs for increase or decrease, in that, energizing the output, depending on your energization/pulse duration, the valve/motor commands increase (or decrease if on the decrease output) position/speed. So, for instance, an energization/pulse length of 1s would give a 2% increase/decrease, whereas an energization/pulse length of 2s would give, say, 3% or 4% increase/decrease? How could we control this using PID? Or is it even possible? Is PULSEGEN applicable in this case? In all this questions, the answer, it seems to me, is negative.

What we have created as a solution for automatic control of the Process Variable through the said binary-output-but-modulating-actuator is a pulser program in that, depending on the error (SP-PV) it would give corresponding pulse in either increment or decrement, with a constant pulse duration (on/off). The problem with this is that it only resembles the Proportional action of the PID controller (not even entirely, because we don't have a variable gain for tuning), that which is totally insufficient to control a dynamic variable with multiple distrubances. And because of this, we are just operating manually, for using this control just makes the process value oscillate. In short, it doesn't work.

What I think as a possible solution is to resemble, at least the Proportional and Integral tuning of the PID controller by making the pulse duration (as gain) and the pulse interval (as integral) variable. But this, still, would be insufficient, for even it seems to resemble the tuning part, it would not resemble the control action (esp. the integral), for, even the pulse is not, say, 1sec on/off, the command/response would still be constant (say .5 sec on/2sec off, constantly)!

Can you please give me any alternative solution?

Thanks for any response!