General Application of Smart Inverters in Distribution and Smart Grid

摘要

The electric grid of the near future will face challenges and opportunities based on two aspects. First, the rapid growth of renewable generations expedites the upgrading of traditional electric grids, allowing more and more distributed generation connected at the customers’ side. Distributed generation units use a wide range of generation technologies, including gas turbines, diesel engines, solar photovoltaics (PV), wind turbines, fuel cells, biomass, and small hydroelectric generators. Under certain penetration level, the grid will experience issues like unexpected voltage rise as well as reverse power flows due to the fluctuation of power production of the distributed generation, especially when using photovoltaic systems. Second, the development of the smart grid encourages using computer-based remote control and automation to modernize utility electricity delivery systems. The two-way communication technology requires that electrical units have additional functions to collect, send and receive data, instead of sending technicians to gather much of the information needed to provide electricity.A grid-connected smart inverter can be the solution to both situations. In this dissertation, an inverter with the ability to generate controllable reactive power during the DC/AC converting process is introduced, which is quite useful in voltage regulation as well as for maintaining desired power factor. Furthermore, this inverter is also designed to perform smart functionalities including islanding detection, ramp rate control, maximum power point tracking and low/high voltage ride through according to the IEEE standards. It also monitors the operation status of the connected PV, sending data to control center in order to help with the management of larger scale of distribution.The research includes the development of an accurate software model of the PV inverter system, and the model validation based on both the simulation results and the lab measurements. Field tests are also designed in order to validate smart inverter’s autonomous functionalities. And the last part of this dissertation discusses the application of smart inverters on a 34-bus distribution system. The inverters and the PV systems will be connected to the original IEEE 34-bus feeder model to do more simulation and validation based on the lab test results of a real grid-connected inverter.