A Voltage Controlled PV Inverter for a Certs Microgrid Applications

Abstract

The Photovoltaic (PV) sources are more compatible for Microgrids because of their ability to internally aggregate and balance with other renewable sources. The conventional grid connected PV inverters are basically current source controlled so unable to control ac voltage or frequency. The PV inverter using the Consortium for Electric Reliability Technology Solutions (CERTS) concepts can control ac voltage and frequency but have a major problem with load transients. The over loaded PV micro source causes dc bus voltage collapse and finally resulting in an ac voltage drop during the load transients. A photovoltaic inverter is capable of operating in both island and grid-connected mode by means of a reconfigurable control scheme. This paper presents an efficient control strategy which causes the PV inverter to act as voltage source to maintain stable dc bus voltage under load transients. With this PV inverter control configuration, it is shown that the PV micro source can operate as a voltage source in the CERTS microgrid. Evolutionary changes in the regulatory and operational climate of traditional electric utilities and the emergence of smaller generating systems such as micro sources have opened new opportunities for on-site power generation by electricity users. In this context, distributed energy resources (DER) - small power generators typically located at users' sites where the energy they generate is used - have emerged as a promising option to meet growing customer needs for electric power with an emphasis on reliability and power quality. The portfolio of DER includes generators, energy storage, load control, and, for certain classes of systems, advanced power electronic interfaces between the generators and the bulk power provider. This paper proposes that the significant potential of smaller DER to meet customers' and utilities' needs can be best captured by organizing these resources into Micro Grids. The Consortium for Electric Reliability Technology Solutions (CERTS) MicroGrid concept assumes an aggregation of loads and micro sources operating as a single system providing both power and heat. The majority of the micro sources must be power electronic based to provide the required flexibility to insure operation as a single aggregated system. This control flexibility allows the CERTS MicroGrid to present itself to the bulk power system as a single controlled unit that meets local needs for reliability and security. The CERTS Micro Grid represents an entirely new approach to integrating DER. Traditional approaches for integrating DER focus on the impacts on grid performance of