Patent ID: 7567064

Claim:
Power conversion system comprising: two or more AC output converter units of a variable AC output voltage, each converter unit including: means for controlling an output voltage converter unit, said means for controlling an output voltage having means to produce two perpendicularly-intersecting reactive and active voltage vectors (u q , u d ) from the output voltage of said converter unit to produce a reactive power component (Q) and an active power component (P), respectively; and means for producing reference signals for controlling the output voltage of said converter in response to the reactive and active power components, wherein said means for producing reference signals for controlling the output voltage includes: inner current control loops; an active power vs. active voltage droop u=u*−mP for generating an active voltage reference signal from the active power component, with u* being the active voltage with P=0 and m being a constant; and a reactive power vs. frequency droop f=f*−nQ to regulate a frequency of the output voltage from the reactive power component, with f* being the frequency with Q=0 and n being a constant.