Abstract

Distributed generation (DG) looks promising for meeting the increasing energy demand with reduced environmental impact. Traditionally, the electric power plants are located far from load centers. DG units based on Photovoltaic (PV), wind, fuel cell etc. can be installed at the distribution level close to the loads, thus reducing investments in the utility's infrastructure. Distributed energy resources, DG plus storage, are connected to the grid by means of power electronic converters. Normally, a single-phase voltage source inverter (VSI) is used as a power interface for low power (< 10 kVA) consumer owned DG units. Its main function is to transfer active power to the grid, but it can also provide reactive power compensation adding value to the DG unit. The reliability of single-phase VSI is relatively low due to the large electrolytic capacitors required at the dc bus for attenuating the 2 nd order voltage ripple. This Thesis discusses a control scheme suitable for the VSI operating with large dc bus ripple, when a small and high reliability thin film capacitor can be used. It is based on a dc bus voltage ripple estimator and a voltage control loop with higher bandwidth. Different types of current controllers were tested for the inner loop but did not affect much the system's performance. An experimental set-up was implemented to show that a variable power factor inverter with a small dc capacitor can perform better than a conventional inverter regarding the transient response and the low frequency harmonic distortion in the ac side current.