OL Contactors are typically used between a motor starter and a Motor, in line, and typically use Bi-Metal Overload contacts which when the current rises to it's rating causes the metal to liquify, releasing a contact stud that rotates releasing a claw that when in a low current condition contacts the non- rotating contact stud providing the current path, when liquified the contact stud rotates, the claw no longer provides contact to the stud and there is no longer a path for the current.
It is true that a system with > 180 deg. phase shift at some low frequency behaves nicely and is completely stable, provided that the phase shift gets back well below 180 degrees at the cross-over frequency. To the human mind - at least mine - it seems very strange why such a system does not oscillate violently, but the math shows it, and so does reality.
Zero voltage switching typically defines an SCR soft start where you either turn the device on or off when the voltage crosses 0 volts in an AC circuit. PWM is a completely different concept where you regulate the amplitude and time of a DC pulse to mimic an AC sign wave with the power devices turning on and off the RMS.