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4 Three-Phase Photovoltaic

Systems: Structures,

Topologies, and Control

Tamás Kerekes, Dezső Séra, and László Máthé

CONTENTS
Abstract ............................................................................................................................................67
4.1 Introduction .............................................................................................................................67
4.2 PV Inverter Structures .............................................................................................................69
4.3 Three-Phase PV Inverter Topologies ......................................................................................71
4.4 Control Building Blocks for PV Inverters ..............................................................................72
4.4.1 Modulation Strategies for Three-Phase PV Inverters .................................................72
4.4.2 Implementation of the Modulation Strategies ............................................................74
4.4.3 Grid Synchronization ..................................................................................................76
4.4.4 Implementation of the PLLs for Grid Synchronization ..............................................78
4.4.5 Current Control ...........................................................................................................81
4.4.6 Implementation of the Current Controllers .................................................................82
4.4.7 Maximum Power Point Tracking ................................................................................82
4.4.8 Grid Integration Functions for PV Systems ................................................................84
4.4.9 Internal Active Power Reserve Management ..............................................................85
4.4.10 Active Power Ramp Limitation ..................................................................................86
4.5 Summary .................................................................................................................................87
References ........................................................................................................................................87

ABSTRACT
Photovoltaic (PV) technology has experienced an unprecedented growth in the last two decades,
transforming from mainly an off-grid niche generation to a major renewable energy technology,
reaching approximately 227 GW of capacity worldwide at the end of 2015 with a predicted extra
50 GW of new installations for 2016 [1]. Large PV power plants interfacing the grid through a
three-phase power electronic converter are now well on the way to become a major player in the
power system in many countries. Therefore, this chapter gives an overview of PV systems with a
focus on three-phase applications from a hardware point of view, detailing the different PV inverter
structures and topologies and discussing the different control layers within a grid-connected PV
plant. Modulation schemes for various PV inverter topologies, grid synchronization, current control,
active and reactive power control, maximum power point tracking, and grid integration requirements
and support functions are also reviewed.

4.1 INTRODUCTION
Renewable energy has become very important both worldwide and on the European market, mainly
due to the decrease in the photovoltaic (PV) system cost (up to 75%) during the last decade. PV has
been the top energy resource in Europe in terms of new installations in 2012, with above 16 GW

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