Low Inertia Systems/Microgrids

NPPT works with low-inertia systems (typically ≤20 MW), including systems with inverter-based sources and systems with distributed architectures (multiple source buses). For these systems, NPPT offers an array of specialized technical and engineering services from project initiation all the way to operation and customer satisfaction assurance, including:

  • EMT or HIL simulation studies in support of planning, design, and operations,to facilitate
    • Selection of inverters, generators/controllers/AVRs, and energy storage
    • Design of controls to meet performance objectives
    • Protection system design and specification
    • Understanding of expected system behavior during events, such as faults, load switching, or on-to-off-grid transitions.
  • Studies of impacts of distributed renewable energy on diesel-based (or similar) systems, and development of interconnection policies and mitigation strategies
  • Design, implementation, testing and monitoring of BESS systems and controls for various forms of low-inertia system support (see NPPT’s BESS capabilities document for more on this)
  • Design, execution and interpretation of tests and commissioning, in the laboratory or in the field
  • Measurement and simulation-based analysis and diagnosis of performance issues in fielded systems
  • Event, failure, and root-cause analysis

NPPT provides these services with an exceptional level of skill, professionalism, responsiveness, and creative but practical thinking. If you have a need that does not appear on this list, please contact us to discuss it.

Example projects


A brief listing of a few relevant recent projects includes the following.

Power system engineering for a whole-feeder microgrid in the northwestern US. This was a 5 MW microgrid comprised of a distribution circuit hosting both diesel generation and PV, and seamless transitions between on-and off-grid modes were desired. Specific duties:
  • Construction of a detailed transient model of the entire system
  • Design of all controls for the battery energy storage system
  • Recommendations for adjustments to generator controls for microgrid compatibility
  • Design of a load-shedding scheme
  • Design, execution and interpretation of system laboratory and field tests
Power system engineering for a battery-inverter system for frequency support on a small island grid.This was a roughly 5 MW diesel-based island grid in which PV penetration levels are becoming high (on an instantaneous power basis, sometimes as high as 90%). Specific duties:
  • Construction of a detailed transient model of the entire island grid
  • Design of all controls for the battery-inverter system
  • Complete system protection and underfrequency load shedding reviews
  • Design and interpretation of system tests
Protection study for a microgrid. NPPT has performed several such studies for microgrids ranging in size from 500 kW to over 3 MW, with rotating plus inverter-based generation as well as storage. Specific duties typically include:
  • Construction of a detailed transient model of the microgrid
  • Quantification of transient fault currents at critical points and for all use cases
  • Design of optimally-coordinated protection for the system, and identification and specification of alternatives to overcurrent protection when necessary
  • Arc flash study for all points at which fault currents were quantified