Harmonic reduction in the parallel arrangements of grid-connected voltage source inverters

The elimination of low order harmonics in grid-connected renewable-energy inverter systems is desirable both from the point of view of grid health as well as efficient inverter operation. In this paper, one inverter (called reference inverter) employs pulse width modulation (PWM) with conventional selective harmonic elimination (SHE) to remove the 5^th and 7^th harmonics. By adjusting a delay in the gating signals to four inverters for example, it is possible also eliminate other higher significant harmonics, namely the 11^th and 13^th harmonics, without any increase in the switching frequency. This approach may be useful for high power grid-connected inverter systems supplied by alternative energy sources where switching losses may become prohibitive if the switching frequency is too high. Two and four parallel inverters systems are investigated and simulated in PSPICE and MATLAB.