AC power quality improvement for line-commutated inverters in photovoltaic applications

The optimization and testing of a line-commutated inverter (LCI) for linking photovoltaic arrays to utility ac systems are reported. A parity simulator is used to optimize both the basic LCI circuit and the prototype device at the operating parameters, ac line = 240 V ac, single phase; dc voltage = 200 V; dc current = 40 A; and firing angle = 160 deg. The design of the harmonic filter and power-factor-compensation network (using the parity simulator to determine the component values) is explained, and the waveforms obtained with the basic, improved-simulation, and improved-prototype LCIs are shown. Although a power-quality standard has not yet been established, the OEM selling price (in quantities of 1000) of a production LCI with power factor 0.88, ITHD 12 percent, and efficiency 93 percent, is estimated at 25 cents/watt, including the required isolation transformer.