PLL structures for utility connected systems

This paper presents a detailed analysis of PLL structures for utility connected systems. The three-phase PLL (phase-locked loop) structure capable of fast tracking the utility voltage vector is studied. A single-phase PLL structure, derived from the three-phase PLL topology, is discussed and its behavior under distorted utility conditions is analyzed. Additionally, the conventional zero-crossing PLL is studied and an alternative implementation for this PLL is proposed in order to improve its dynamic behavior. Simulation and experimental results from a DSP-based system are included to support the theoretical analysis.

I. Introduction

The phase angle of the utility voltage vector is a basic information for an increasing number of grid-connected power conditioning equipments, such as AC/DC converters, uninterruptible power systems (UPS), series voltage compensators and the emerging distributed generation systems. In such applications, an accurate and fast detection of the phase angle of the utility voltage is essential to assure the correct generation of the reference signals. Thus, phase-locked loop (PLL) topologies must handle distorted utility voltages if they are intended to applications that require the tracking of the utility voltage vector [1]–[5].