Plural parallel bridge inverter power conversion system with balanced DC input currents

Claim 1

A power conversion system, comprising: a DC power source; a plurality of unit converters; each being composed of a bridge connected switching devices for converting a DC power to an AC power; a plurality of DC reactors; each being provided between said DC power source and one of said unit converters, respectively; each of said unit converters having DC terminals connected to said DC power source through one of said DC reactors, respectively, and having AC terminals of each phase; said AC terminals of each phase of said unit converters being connected in common and being adapted for connecting to an AC load; and control means including, current instruction value generating means for generating current instruction values of each phase for AC output currents of each phase of said power conversion system, AC voltage detection means for detecting AC output voltages of each phase of said power conversion system, DC current detection means for detecting a plurality of DC currents, each flowing between said DC power source and one of said unit converters, respectively, conduction arm number calculating means for determining conduction arm numbers of said unit converters of each phase, each being determined based on a ratio of said current instruction value of respective phase and a mean value of said DC currents, and current balance control means connected to receive said conduction arm numbers from said conduction arm number calculating means, said AC output voltages from said AC voltage detection means, and said DC currents from said DC current detection means, for generating a plurality of conduction instructions for said switching devices at a time of change of one of said conduction arm numbers based on a first order of magnitude of said AC voltages, a second order of magnitude of said DC currents and said conduction arm numbers of each phase at that point; said conduction instructions being applied to said unit converters for switching ON or OFF said switching devices; thereby balance control of said DC currents of said unit converters being exercised.