Design of a Non-PLL Grid-Forming Inverter for Smooth Microgrid Transition Operation

Jing Wang, Blake Lundstrom, Andrey Bernstein

Research output: NRELPresentation


This paper develops a controller for a grid-forming (GFM) inverter that is capable of operating as either a GFM or grid-feeding source that can improve the operation of a microgrid during on-off grid transitions through use of a novel synchronization approach. Furthermore, this controller avoids use of a phase-locked loop (PLL) and the inverter is able to synchronize with the grid with self-generated voltage and frequency. This prevents the inverter from replicating any grid voltage disturbances in its output - a key disadvantage of many grid-connected inverters that use a PLL. To enable fast synchronization, active synchronization control is adopted both during inverter start-up and microgrid reconnection operation and a method of coordinating synchronization of the inverter with a microgrid controller and grid interconnection circuit breaker is presented. Simulation results for multiple microgrid transition operations and unplanned islanding events demonstrate that the developed non-PLL grid-connected GFM inverter controller and synchronization method are effective in synchronizing the inverter and microgrid to the grid, avoiding phase jump during microgrid transition operation, and improving microgrid islanding transients versus a traditional configuration.
Original languageAmerican English
Number of pages6
StatePublished - 2020

Publication series

NamePresented at the IEEE Power and Energy General Meeting (PES), 3-6 August 2020

NREL Publication Number

  • NREL/PR-5D00-77338


  • active synchronization control
  • grid-feeding
  • grid-forming
  • microgrid transition operation
  • non-PLL


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