Phase Locked Loop(PLL)

Introduction

PLL (PhaseLocked Loop) circuits are used in Dual Active Bridge (DAB) converters for the purpose of modulating control signals. This is mainly to control power transfer through phase-shift modulation. The PLL circuit accurately detects the phase of the input signal and synchronizes it with the reference signal, thereby adjusting the phase difference between the two bridges of the DAB converter. This maximizes power transfer efficiency and ensures stable operation of the converter. Due to these characteristics, PLLs play an important role in DAB converters. In addition, PLLs are used as essential components in various fields such as communication systems, signal processing, and clock generation.

 

Linearized Small Signal Model of a PLL

 

Phase Detector(PD)

Loop Filter(LF)

Voltage Controlled Oscillator(VCO)

Closed-loop phase transfer function

2nd  Order Transfer function normalization

Design: ts=0.1[s]

 

Linear Model

Nonlinear Model Analysis

PLL Block model

Input signal

Input signal

Output signal

Output signal

Phase Detector(PD)

The Phase error Signal from PD output

Loop Filter(LF)

 

Voltage Controlled Oscillator(VCO)

Why do we need a notch filter?

Frequency jump 50[Hz] to 45[Hz]

Phase jump 0[Deg] to 45[Deg]

Notch filter

 

Notcj filter Bode-plot

Nonlinear PLL with Notch filter

Reference

[GRID CONVERTERS FOR PHOTOVOLTAIC AND WIND POWER SYSTEMS], Remus Teodorescu, Marco Liserre, Pedro Rodr´ıguez