Self-Synchronized Universal Droop Controller

Qing-Chang Zhong,Wen-Long Ming,Yu Zeng

doi:10.1109/access.2016.2616115

Abstract

In this paper, a self-synchronization mechanism is embedded into the universal droop controller (UDC), which is applicable to inverters having an impedance angle between $-{\pi }/{2}$ rad and ${\pi }/{2}$ rad, to form a self-synchronized UDC (SUDC). Both the voltage loop and the frequency loop of the UDC are modified to facilitate the standalone and grid-connected operation of inverters. Importantly, the dedicated phase-locked-loop that is often needed for grid-connected or parallel-operated converters is removed. The inverter is able to achieve synchronization before and after connection without the need of a dedicated synchronization unit. Since the original structure of the UDC is kept in the SUDC, the properties of the UDC, such as accurate power sharing and tight output voltage regulation, are well maintained. Extensive experimental results are presented to demonstrate the performance of the proposed SUDC for a grid-connected single-phase inverter.

Highlights

Due to global warming and environmental crisis, renewable energy systems in smart grids, e.g., wind, solar and tidal power, have been extensively studied during the last few decades [1]–[3]
In order to achieve accurate proportional sharing, it was required that the inverters in parallel operation should have the same perunit output impedance, which is difficult to be satisfied in practice
In this paper, a self-synchronized universal droop controller has been proposed for inverters

Summary

INTRODUCTION

Due to global warming and environmental crisis, renewable energy systems in smart grids, e.g., wind, solar and tidal power, have been extensively studied during the last few decades [1]–[3]. When the amount of such renewable energy exceeds a certain level, it is inevitable that they will be required to take part in the regulation of system frequency and voltage in smart grids This means numerous power inverters will be connected to the power grid, which are practically operated in parallel. It has been shown that the droop controller and the enhanced phase-locked loops structurally resemble each other [23], [24] This provides the theoretical explanation why the dedicated synchronization unit could be removed. The original structure of the UDC is well maintained so that accurate proportional power sharing and tight voltage regulation can be achieved, for inverters having an output impedance angle between.

OVERVIEW OF THE UNIVERSAL DROOP

EXPERIMENTAL VALIDATION

Findings

CONCLUSIONS