Design and commissioning of 2.5 MW DC supply for evaluating megawatt scale smart solar inverters

Abstract

Utility scale photovoltaic plants often use megawatt scale central inverters with high efficiency and power density. Inverter manufacturers now offer solutions over 2 MW for 1000 V DC class PV arrays. Certifying inverters at this power level can present test equipment design and procurement challenges. This paper describes a retrofit of an existing medium voltage, 9-level TECO Westinghouse VersaBridge series connected H-bridge (SCHB) inverter to supply DC power up to 2500 A at 1000 V for central inverter testing. Simulations in PLECS and controller hardware-in-the-loop experiments with RTDS were used for initial controller design. The SCHB pulse-width modulation scheme led to an interleaved output stage topology in a six parallel module configuration without requiring modification to the existing VersaBridge controller. Commissioning results are shown along with experimental results for the first inverter test article at 2500 A, 900 V.