Field Tests of a Novel Inverter for Photovoltaic Power Conditioning

摘要

The Dickerson inverter synthesizes a sinewave current from a photovoltaic array that is segmented into a number of subarrays. These subarrays are switched among the ac phases so that the current from a given subarray is continuous, and each phase is connected at all times to one or more subarrays. The control scheme assures a near-unity power factor current with real-time phase adjustment to power-system disturbances. A prototype inverter was operated into a three-phase power system, with the dc supplied by a photovoltaic array at Sandia National Laboratories. The results of these tests under normal, abnormal and fault conditions are reported. Inversion efficiencies up to 99% were achieved with 0.97 power factor. A simple filter reduced current harmonics from 18% to 5%. The performance for the inverter was projected for a 480-V, three-phase system at the 50-kVA level. An analysis of filtering costs indicates that harmonic reduction to 5% can be achieved at under $0.003 per watt for typical central-station applications. The intended power range for these inverters is 50--250 kVA. The cost to produce the inverter at the 50-kVA level in quantities of 1000 units is estimated to be $0.05 per watt, which is less than the projected cost of other 50-kVA inverters. 22 figs., 9 tabs.