Space Vector Modulation Controlled Three-Level Converter for Ocean Wave Energy Conversion Ilknur Colak Ahmet Derya Kocabas Senior Research Engineer Asst. Prof., Electrical Eng. Dep. ABB Switzerland Ltd. Istanbul Technical University CH-5300 Turgi 34469 Maslak Istanbul Switzerland Turkey Abstract – Ocean wave energy is one of the high potential renewable energy sources. Due to the recent progresses in the OWEC (Ocean Wave Energy Conversion) devices, higher power extraction is possible which also brings the need to use multilevel converters to increase the voltage as well as the power. In this study, adaption of the NTV-SV-PWM method to the multilevel converter which is used for OWEC is proposed. Here the aim is to bring the newest power electronic methods to the ocean wave energy conversion technologies and improve the energy extraction efficiency and the quality of the power transferred to the grid. Keywords – NTV-SV-PWM, Wave Energy Conversion, NPC, OWC. I. INTRODUCTION In recent years, there is an increasing research trend towards wave energy conversion to fulfill the energy requirements around the world. In parallel, there is a growing interest in multilevel topologies to increase the power and voltage ratings of the power converters [1], [2]. However in the literature there are no wide researches or applications where the advanced power electronics topologies and the control methodologies are applied for the wave energy conversion systems. Therefore, in this study it’s aimed to combine different engineering disciplines into the same application and bring these new and sophisticated approaches into the renewable energy applications. As a first step of the study, the wave energy characteristics are analyzed and a mathematical wave model is generated in Matlab to simulate the power extraction from wave energy. A floating oscillating water column (OWC) wave energy conversion system is used to transform the wave energy to kinetic energy. The operating principle of the OWC is based on transforming hydrodynamic wave action into reciprocating airflow. The OWC device consists basically of a large wave capture chamber and a platform for a power take off device (PTO). In this application a Wells turbine is chosen as PTO device and coupled to a generator to convert the mechanical energy to electrical energy, as it is presented in Fig. 1 [3]. Following that, the electrical energy on the output of the generator is converted to DC voltage with a three level active rectifier (3L-NPC) which enables bidirectional current flow between AC input and the DC link. In this study the rectifier controls the total DC link voltage and extracts the maximum power from the generator’s terminal with a unity power factor. 3L-DC/AC Converter DC Link Capacitors Air Generator Water movement Water level Air turbine Air flow 3L-AC/DC Converter C2 S1 D1 S2 D2 S3 D3 S4 D4 S5 D5 S6 D6 S7 D7 S8 D8 S9 D9 S10 D10 S11 D11 S12 D12 C1 Do1 Do2 Do3 Do4 Do5 Do6 + - + Vd/2 Vd/2 p o n - Fig. 1. System diagram. Uniform air pressure