Patent ID: 6381157
Filing Date: 2002-04-30
Classification: H02M

Abstract:
A method for independent load sharing of current harmonics between parallel inverter units (1a, 1b, 1c; 22a, 22b, 22c) in an AC power system without intra-unit control signal communication, each of said inverter units comprising a DC to AC converter means (2; 23) with associated control means (5; 26) for controlling switching times of said converter means and each being connected to a common load (8; 29) through a separate impedance (7a, 7b, 7c; 28a, 28b, 28c), said method comprising for each of said units the steps of measuring at least a current in a power output line (51a, 51b, 51c) from the unit before said separate impedance, processing the measured current value for determination of amplitude and phase of a reference signal component (Vh) corresponding to a selected harmonic (Ih)of said measured current, comparing the amplitude and phase of said reference signal component with amplitude and phase of a feed-back voltage or current (V) from said power output line to produce an error signal and using said error signal for determination of a control signal component for the selected harmonic for incorporation into a control signal input to said control means (5; 26) for controlling the content of said harmonic in the voltage and/or current supplied by the inverter unit (1a, 1b, 1c; 22a, 22b, 22c) to the common load (8; 29) via said separate impedance (7a, 7b, 7c; 28a, 28b, 28c).