Development and test of a four-module 1200 kVA distributed generation power plant

MTechnology, Inc., was retained to design and develop the power electronics system for a distributed generation power plant. The plant incorporated four 250 kW DC modules. The plant was required to operate both in grid-connect and grid-independent modes, with constraints upon the acceptable transients applied to the plant internal bus during transitions between modes. The transition from grid-connect to grid-independent mode required the plant power control system to assume responsibility for voltage regulation and power balance between generation and plant ancillary loads. Operation in grid-independent mode faced the challenge of starting relatively large compressor and fan loads, variable generation and load power levels, and the requirement to clear faults on the internal plant bus. The inverter controls were designed to supply up to 2x rated continuous output current into low voltage and fault conditions, with minimal disturbance of the DC power flow from the DER modules. This elevated current simplified coordination with protective devices on the customer and utility network.