Micro-grids with distributed generators in an edge-of-main grid scenario

Milambo Majwi

This thesis investigates the dynamic behaviour and transients of a sub-system when operating in two scenarios: Grid-connected mode, and islanding mode. The sub-system consists of two distributed generators (DGs). One DG is modeled using a rotating synchronous machine fitted with a governor to represent a diesel generator, while the other is modeled using a DC voltage source and a converter to represent a photovoltaic (PV) energy source. The distribution network also consists of a grid connected source known as the main grid. During normal operation, the supply of electricity to the connected loads is shared among the three energy sources, the DGs supplying about 80 percent of the loads and the rest are supplied by the main grid. When the main grid is disconnected from the network, supply to the connected loads is shared by the two DGs. The PV energy source system is equipped with real and reactive power control mechanisms that minimize islanding transients and maintain angle stability and voltage quality of the network. The study includes examples of micro-grid transient analysis carried out in the past. This is followed by the study of how transient analysis can be carried out in PowerFactory software. The simulation studies show that the electronic power control system in a PV generator is capable of maintaining the angle stability of a micro grid in response to transient conditions. These transients may result from changes in power demands from connected loads or severe islanding events. The diesel generator through the use of a governor responds to supply the required power to the system when the PV has reached its maximum supply limits. The diesel generator acts as a back-up to the PV supply.

Micro-grids with distributed generators in an edge-of-main grid scenario

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