Droop Control Methods for PV-Based Mini Grids with Different Line Resistances and Impedances

Nicholas Nixon Opiyo

doi:10.4236/sgre.2018.96007

Abstract

Different droop control methods for PV-based communal grid networks (minigrids and microgrids) with different line resistances (R) and impedances (X) are modelled and simulated in MATLAB to determine the most efficient control method for a given network. Results show that active power-frequency (P-f) droop control method is the most efficient for low voltage transmission networks with low X/R ratios while reactive power-voltage (Q-V) droop control method is the most efficient for systems with high X/R ratios. For systems with complex line resistances and impedances, i.e. near unity X/R ratios, P-f or Q-V droop methods cannot individually efficiently regulate line voltage and frequency. For such systems, P-Q-f droop control method, where both active and reactive power could be used to control PCC voltage via shunt-connected inverters, is determined to be the most efficient control method. Results also show that shunt-connection of inverters leads to improved power flow control of interconnected communal grids by allowing feeder voltage regulation, load reactive power support, reactive power management between feeders, and improved overall system performance against dynamic disturbances.

Highlights

A PV-based communal grid can be defined as a collection of distributed PV systems, distributed energy storage devices, and distributed loads, operating as a single and controllable system capable of supplying power to an area of service
Results show that shunt-connection of inverters leads to improved power flow control of interconnected communal grids by allowing feeder voltage regulation, load reactive power support, reactive power management between feeders, and improved overall system performance against dynamic disturbances
If point of common coupling (PCC) voltage rises by more than 5%, another distributed PV generator is used to inject active power into the system while if PCC voltage drops below 5% a heavy load is connected to feeder 2

Summary

Introduction

A PV-based communal grid can be defined as a collection of distributed PV systems, distributed energy storage devices, and distributed loads, operating as a single and controllable system capable of supplying power to an area of service. They should be operable in both grid-connected and islanded modes. These factors influence the control strategy applied for a communal grid and will need to give consideration to issues such as load sensitivity, number of distributed generators in the communal grid, power quality requirements, ownership of the communal grid and distributed generators, distances between the distributed generators, the existing communication infrastructure, each distributed generator’s energy source, and whether the communal grid is predominantly and exporter or importer of electricity [3] [4] [5]

Methods

Results

Conclusion