Technique for Seamless Transition of Voltage-Source Inverters Between Standalone and Grid-Tied Modes 
Reference Number: 13-01
Inventors: Behrooz Mirafzal and David Ochs
Description:

When voltage-source inverters are designed to operate in both standalone and grid-tied modes, they must withstand large transient overcurrents that occur when the inverter connects to the grid. This occurs because the grid and point of common coupling (PCC) voltages are out of phase, and the inverter isn’t able to quickly recognize the change fast enough. Currently, a controllable static transfer switch (STS) is almost always required to prevent this from occurring.

Researchers at Kansas State University have created a technique allowing voltage-source inverters to seamlessly transition between standalone and grid-tied modes, without the use of a controllable STS. This process includes a method for quickly determining when the inverter has been connected to the grid. A novel algorithm estimates the grid angle almost instantly, prompting the inverter to respond and prevent large currents from flowing. The technique’s fast response allows the inverter to return to normal operation very quickly, and utilizes only the inverter current and voltage sensors during the process.

Advantages:
  • Decreased cost and increased reliability of grid-tied inverters
  • Eliminates transient overcurrent and need for a controllable STS
  • Returns inverter to normal operation faster
  • Reduced number of needed sensors
Applications:
  • Reduces the number of needed sensors for inverters already using a controllable STS
  • Reduces wear and increases lifespan of inverters that do not use any STS
  • Makes possible the use of a non-controllable STS
  • Eliminates need for any STS in systems that do not require inverter disconnect from the grid (more likely with increased use of wind, solar)
Patent Status:
  • Provisional patent application filed in March 2013.

Kansas State University Research Foundation seeks to have discussions with companies that are interested in licensing and/or research collaborations.

Interested parties should contact:

Kansas State University Institute for Commercialization (KSU-IC)
2005 Research Park Circle Manhattan, KS 66502
Tel: 785-532-3900 Fax: 785-532-3909
E-Mail: ic@k-state.edu