Implementation of a control strategy for elimination of voltage harmonics in inverters

A simple procedure is proposed in this paper for eliminating harmonics in the load voltage of stand-alone single-phase inverters, while supplying non-linear loads. An observer has been designed for estimating the fundamental component and hence the harmonics present in the load voltage. Assuming that the Inverter could be modeled as a feed back control system with the fundamental component as the desired output, the harmonics take the role of noise creeping into the output. The well-known control strategy of using a large feed back around the noise signal is employed, to reduce its effect at the output, so that, even with non-linear loads the output voltage waveform is smoother, exhibiting low or negligible total harmonic distortion. The efficiency of the estimation of the harmonics for feedback depends on the observer pole location. The system can be easily modeled in continuous-time domain; however, the ideas can be directly implanted digitally into single-phase inverters controlled by FPGA or DSP chips.