How to implement a phase-continuous grid frequency step in PLECS?

I am simulating a three-phase grid-forming inverter. At t = 1 s, I want the grid frequency to change from 50 Hz to 49.9 Hz. However, directly changing the frequency of the built-in three-phase AC voltage source appears to cause a phase jump, because its voltage is calculated as: v(t) = Vm*sin(w*t + phi) Changing w directly therefore changes w*t instantaneously and produces a large artificial power transient. I want the frequency to step while the phase remains continuous. The phase should be calculated as: theta(t) = theta(0) + integral from 0 to t of w(tau) d(tau) What is the recommended way to implement this in PLECS?