Within Simulink, we can use the "Measure voltage" to get a numerical representation (Simulink Signal) of the voltage and use it for mathematical operations. Does there exist a way to take a numerical representation (Simulink Signal) and convert it into a voltage signal that I can send through an inverter or rectifier?
I assume you are referring to Simscape/SimPowerSystems. The answer is yes, use the Controlled Voltage Source block from the Electrical Sources library of Simscape or the equivalent Controlled Voltage Source block from the Electrical Sources library of SimPowerSystems (if you use the old generation library of SimPowerSystems, the new one is Simscape-based so you can use the Simscape blocks).