Utility Scale PV/Wind

NPPT performs a variety of services for owners and operators of utility-scale PV plants, 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.
  • 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.

Temporary/transient overvoltage analysis of utility-scale PV NPPT has done several studies of this type. Specific duties:
  • Work directly with inverter manufacturers to ensure model accuracy
  • Perform EMT simulations of load-rejection and ground-fault events
  • Determine energy-handling adequacy of specified arresters, and re-spec as indicated
Ride-through compliance of a wind farm during switching of nearby A large transmission-connected wind farm was analyzed to determine whether it would properly ride through the switching of nearby transmission-connected capacitors. Specific duties:
  • Development of EMT model of the WTs, other local generation, a local nonlinear load, and the capacitor banks and switchgear
  • EMT studies to ascertain impact of capacitor switching on transmission voltages and on the WT plant
  • Conclusion: NPPT recommended independent-pole switching to minimize capacitor transients and facilitate proper operation of the WT plant and other nearby sensitive loads.
Event/failure analysis: analysis of an event that led to the failure of all inverters and all tracker motors in a 50 MW PV plant. Some form of overvoltage was suspected, but the root cause and mechanism were not known. Specific duties:
  • Study and become familiar with the plant
  • Analyze event data
  • Visit site and confer with plant engineers
  • Work with inverter manufacturer to obtain necessary product details
  • Perform detailed EMT modeling to test theories
  • Conclusion: event was caused by ferroresonance between the plant underground collector system capacitance and the magnetizing inductance of the main plant transformer. Mitigation/avoidance strategies were developed and implemented.
Event/failure analysis: repeated failure of specific inverters in a large (> 100 MW) PV plant. IGBT failures were occurring, but only, and repeatably, for certain inverters within the plant. Another nearly identical plant about twenty miles away was experiencing no such failures. Specific duties:
  • Work closely with the inverter manufacturer to understand the details of the design
  • Study and become familiar with the plant
  • Analyze event data
  • Specify necessary measurements and verifications on-site
  • Perform detailed EMT simulations to test theories
  • Conclusion: the problem was arising because of a combination of a grounding problem (which only manifest at certain locations due to highly non uniform impedance to remote earth across the plant footprint), and a somewhat marginal inverter design that pushed the IGBTs close to their operational limits.