Photo - Voltaic Negative Conductance in AC Power Gird and Its Effect on the AC Voltage Waveform

Conventional thinking abhors inputting any current harmonic into the city power grid, and has hindered the entrance of photovoltaic power as the urban electrical source. Most modern electrical loads, however, are in fact the current harmonic generators, and unavoidably the line voltage is distorted. Regulations on harmonics should be reviewed, and efforts made to better cope with the harmonics. The new solar-to-ac converter (STAC)** provides conversion of solar photovoltaic into AC power by emulating a negative conductance load to the line voltage. As small-power sources distributed over the city, the current harmonic from STAC act to cancel the effect of the harmonic from other loads, resulting in less voltage waveform distortion in the city lines. This paper describes the underlying reasons for the beneficial current harmonic, and presents experimental results to illustrate "voltage waveform strengthening" when the non-liner positive load's effect are canceled by the non-liner negative conductance of the STAC-operated solar cells. Inverter-operated solar cells on the other hand may cause higher harmonic contents and even short circuit in the city lines. In a properly power-factor-controlled city grid, STAC-operated solar power is now ready for large scale consumption.