Power supply for dirvers in 3-phase motors - multiple transfromer windings
Each IGBT needs a gate signal that is relative to its own emitter terminal.

The emitter terminals of all of the low-side IGBTs are connected together, so their drivers can share a common power supply.

However, each of the high-side IGBT emitters is at the voltage level of its own unique phase output, which means that each one's driver needs an independent power supply that can "float" independently of all of the others.