A Brushless of this type of motors for Hobbies works with a DC Input, however, the ESC does a similar function as a typical DC-AC Inverter, it creates a 3 phase AC output from a DC input. Normally a sensorless type uses only two phase for the commutation, while the third is used for positioning sensing.
There is not a "steady" ground wire here, since they are all going through zero on a sequencing bases.
The ESC besides the DC-AC conversion it also pulses and synch the waves in a timely fashion through an Oscillator and according to accel of the V.R. (Variable Resistor) and C.L.(Current Limit) set .