Investigation of Microgrid Controllers for Improved Transient Response

Abstract

The concept of operating the distributed energy resources (DER) to supply electricity for the local loads has led to the development of microgrids. Most of the DERs in microgrids are driven by voltage source inverters (VSI) based power electronic converters to interface the DERs with loads and grid. The primary objective of microgrids operating in either grid connected or islanded mode is to deliver the required active and reactive power while maintaining newlinevoltage and frequency within limits. During grid connected mode, the utility grid being very strong takes care of any disturbances and sudden load demands. The real challenge in microgrid operation is during its islanded mode of operation during which it lacks of any support from the utility grid. Further, uncertainty in generation from renewable energy based DERs,very small or no reserve capacity of DERs, and the inability of the static VSIs to provide kinetic energy support, are the key reasons that are affecting the output of microgrids under any newlinetransients. Thus, addressing transient response has become a major challenge. newlineUnder transient conditions, especially during islanded mode of operation, VSIs with a newlineproper control will help in achieving better transient response i.e., a) better maintenance of voltage and frequency within limits, and b) better power delivering capability. In view of this,the objective of this thesis is to propose an effective multiloop VSI controller for enhancing newlinethe transient response of microgrids under sudden large load changes during its islanded mode of operation. newlineCascaded power-voltage-current controller is a common VSI control scheme to achieve newlinebetter transient response under sudden and large load demands. This is a multiloop controller which comprise of power controller in the outer loop and voltage-current (VA) controllers in the inner loops. The response of VSI based renewable energy microgrids depends on the effectiveness of the power and VA controllers. Usually, power controllers with fixed droop possess limited p