Patent ID: 7327588
Filing Date: 2008-02-05
Classification: H02M

Abstract:
1. A method for synchronizing parallel-connected inverter units, said inverters including inverter-specific modulators, or parallel-connected frequency converters re-injecting braking energy into a supply network, said frequency converters having inverter unit-specific modulators both in the mains bridges and in the load bridges, the method comprising; measuring the circulating current between the inverter units; and synchronizing the modulators to each other on the basis of the current measurement data; wherein measuring the circulating current, in the inverter units functioning as mains inverters or in the frequency converters, includes: measuring the base current simultaneously and forming a sum of the phase currents; detecting the instantaneous value of switching-frequency circulating current by multiplying the sum of the phase currents by the polarity of a triangular wave or a corresponding modulation signal; and forming a circulating current sum by summing the successive instantaneous value results.