Design Characteristics of High-Power PV Inverters

While high-power PV installations certainly vary in configuration, a typical commercially installed system (Figure 1) consists of the following: • PV modules stacked in strings not to exceed 600 V open-load, referenced to ground on either positive or negative leg • A UL1741-certified inverter whose function, in addition to converting direct current to alternating current, is to act as an autonomous generating station; This includes functions as varied as optimally extracting energy from the array to assuring National Electric Code (NEC)-compliant operation for the entire facility. • An isolating transformer to provide galvanic separation of the PV facility from the electric utility, in addition to voltage ratio-changing (This may, or may not, be provided integrally with the inverter.) • Point of common coupling (PCC) to the utility, which may be either a low-voltage (≤ 600 V) distribution system of arbitrary size (with any type or quantity of three-phase appliances) or a dedicated connection to the low-voltage secondary of a medium-voltage utility transformer