Analysis of Operating Modes of the Novel Isolated Interface Converter for PMSG Based Wind Turbines Lauris Bisenieks 1,2 , Dmitri Vinnikov 1 , Janis Zakis 1 1 Department of Electrical Drives and Power Electronics, Tallinn University of Technology (Tallinn, Estonia) 2 Institute of Industrial Electronics and Electrical Engineering, Riga Technical University (Riga, Latvia) lauris.bisenieks@rtu.lv , dmitri.vinnikov@ieee.org , janis.zakis@ieee.org Abstract- This paper presents a new converter topology for a permanent magnet synchronous generator based variable speed wind turbine. Main emphasis is on the combination of a controlled rectifier and a novel step-up isolated DC/DC converter topology proposed by the authors. The topology (controlled rectifier coupled with a quasi-Z-source based galvanically isolated step-up DC/DC converter) is essential to generate regulated DC voltage (400 V DC typical for 230 V AC output) despite wide variations in the output voltage of a wind generator. The operation principle of the proposed topology is described in detail. Experimental results are presented and analyzed. I. INTRODUCTION Different types of generators can be used in wind energy conversion systems (WECS), but permanent magnet synchronous generators (PMSG) dominate the market [1]. The main advantage of PMSG is the possibility of multipole design that offers slow speed operation and the possibility of gearless WECS construction. Another advantage is the maintenance free operation since there are no brushes. The main drawback of PMSG is the dependence of its output voltage on the rotation speed. In the variable speed wind turbine applications the minimum and the maximum voltage values may differ for four times [1]. This drawback can be easily overcome with the help of an appropriate interface converter. The interface converter rectifies the input AC with variable voltage and frequency, adjusts voltage levels and inverts DC voltage into AC with the grid voltage and frequency. Additionally, it should have maximum power point tracking (MPPT) functionality to extract more power from the wind. Different topologies of the interfacing converter are discussed in the literature [1-6]. Basically, they can be categorized as topologies with HF isolation [3,4] and those without isolation [5,6]. This paper is devoted to the isolated topologies, i.e. where the generator and grid sides are galvanically isolated by means of a high-frequency transformer. In 2010 researchers of the Department of Electrical Drives and Power Electronics of Tallinn University of Technology proposed a new type of an isolated interface converter for PMSG based wind turbines (Fig. 1). The proposed interface converter utilizes the multistage energy conversion. First, the controlled rectifier converts the variable voltage with the variable frequency U gen from the PMSG into a DC voltage U DC1 . The qZS DC/DC converter offers galvanic isolation and voltage level adjustment between the generator side and the grid side DC links. Utilization of a unique qZS network and appropriate control offers an additional voltage regulation freedom at high efficiency. In such a way both converters together are responsible for the stabilized grid side DC link voltage U DC2 . Converter operation modes at different wind speeds for the particular application with 1.3 kW PMSG are illustrated in Fig. 2. It is seen that the demanded voltage boost could be obtained in two steps. First, the controlled rectifier stabilizes the generator side DC link voltage U DC1 to a 150 V level when the PMSG voltage is in the range between 45 V at cut- in conditions and below 112 V. The generator-side rectifier works as an uncontrolled rectifier when the PMSG voltage U gen is above 112 V. In this mode the voltage U DC1 is changing proportionally to the PMSG voltage, from 150 V in the rated speed conditions up to 250 V near the cut-off point. After the rectifier, the qZS based step-up DC/DC converter finally stabilizes the grid side DC link voltage U DC2 at 400 V DC despite variations in the generator side DC link voltage U DC1 in the range from 150 V to 250 V and also provides the demanded galvanic isolation. Fig. 1. Power circuit of the proposed interface converter. Proceedings of the 2011 International Conference on Power Engineering, Energy and Electrical Drives Torremolinos (Málaga), Spain. May 2011 978-1-4244-9843-7/11/$26.00 ©2011 IEEE