Robust Droop Control for Parallel Operated Inverters

Technology #d-1301

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Beibei Ren
Mechanical Engineering, Texas Tech University, Lubbock, TX
Yeqin Wang
Mechanical Engineering, Texas Tech University, Lubbock, TX
Qing-Chang Zhong
Mechanical Engineering, Texas Tech University, Lubbock, TX
Managed By
Cameron Smith
Licensing Associate 806-834-6822
Patent Protection

Provisional Patent Application Filed

The use of renewable energy technologies, such as wind and solar energy, is vastly increasing. With their increasing use, their incorporation into power grids is essential to use the energy they produce. The incorporation of these technologies into these grids requires the use of devices that turn direct current into alternating current called power inverters. Because of the high demand for power and the growing capacity for these renewable energy technologies to supply this demand, power electronic devices need to be able to handle the increased demand. Power inverters are currently used in parallel to accommodate the high demand for electrical energy in power grids. When the power inverters are used in parallel to allow parallel power generation, it is often referred to as load sharing. Droop control is a control strategy commonly applied to power generators to allow load sharing. It allows for equal load balancing between inverters, but requires that output impedance be matched between said inverters. This results in inaccurate reactive power sharing. Traditional droop control strategies are also unable to handle system disturbances, such as large or quick load changes, variations in output impedances, and fluctuating DC-link voltages. 

This technology provides a modification to the conventional droop control systems that is able to handle these system disturbances to allow accurate proportional load sharing among parallel-operated inverters. It reduces high-frequency noise frequencies that occur during the switching of harmonics and sampling disturbances. It differs from similar methods because in can compensate for uncertainties and system disturbances. Other droop control methods can only adjust for variations in inverter output impedances and require external regulators. This technology can adjust not only for varying output impedances, but for drastic load changes and fluctuating DC-link voltages that can occur in practical applications without requiring external regulatory devices. 

Reference Number: D-1301 

Market Applications: 

  • Energy distribution
  • Energy systems and power grids 

Features, Benefits, & Advantages:

  • Improved reactive power sharing accuracy between parallel inverters used in power grids
  • Improved transient performance between parallel inverters
  • Improve management of system disturbances, such as drastic load changes, variations of output impedance, and fluctuating DC-link voltage
  • Power grids no longer have to worry about matching output impedances of parallel inverters 

Intellectual Property: A provisional application, serial number 62/394,303, was filed on September 14th, 2016. 

Development Stage: A prototype system of the disclosed technology has been tested and verified in a relevant environment. The invention is ready for testing in an actual operation system for further development. 


  • Beibei Ren, Mechanical Engineering, Texas Tech University, Lubbock, TX
  • Yeqin Wang, Mechanical Engineering, Texas Tech University, Lubbock, TX
  • Qing-Chang Zhong, Mechanical Engineering, Texas Tech University, Lubbock, TX 

Keywords: droop control, utility grid, microgrid, grid