Communicationless hot-swap paralleling of three-phase inverters with isochronous frequency

This paper presents a technology used for communicationless hot-swap parallel operation of three-phase inverters with isochronous frequency. This novel technology is implemented within auxiliary power distribution systems used to deliver 50 Hz, 60 Hz or 400 Hz three-phase, four-wire power to remote locations from a variable DC power supply (engine, generator, battery bank). The regulation of the output voltage waveform during operation of each individual converter is ensured with a special algorithm. Blanking time, zero-current clamping, and the cross-coupling inductive terms are compensated from the instantaneous phase current. This new algorithm allows multiple identical units to work on the same three-phase AC bus in a parallel manner. The parallel operation includes a start-up and synchronization algorithm able to provide hot-swap operation. The conventional droop coefficient method is herein transformed into a non-linear controller able to satisfy the requirements of isochronous frequency operation. Such requirement is imposed by operation of military or medical equipments based on a constant grid frequency.