A REVIEW ON IMPLEMENTATION OF THREE-PHASE TWO-STAGE GRID-CONNECTED MIC

Module integrated converters (MICs) in single phase have witnessed recent market success due to unique features such as improved energy harvest,improved system efficiency,lower installation costs,plug - and - play operation,and enhanced flexibility and mo dularity. The MIC sector has grown from a niche market to mainstream,especially in the United States. Assuming further expansion of the MIC market,this paper presents the micro inverter concept incorporated in large size photovoltaic (PV) installations such as megawatts (MW) - class solar farms where a three - phase ac connection is employed. A high - efficiency three - phase MIC with two - stage zero voltage switching (ZVS) operation for the grid - tied PV system is proposed which will reduce cost per watt,improve re - liability,and increase scalability of MW - class solar farms through the development of new solar farm system architectures. The first stage consists of a high - efficiency full - bridge LLC resonant dc � dc converter which interfaces to the PV panel and prod uces a dc - link voltage. A center points iteration algorithm developed specifically for LLC resonant topologies is used to track the maximum power point of the PV panel. The second stage is comprised of a three - phase dc � ac inverter circuit which employs a s imple soft - switching scheme without adding auxiliary components. The modeling and control strategy of this three - phase dc � ac inverter is described. Because the dc - link capacitor plays such an important role for dual - stage MIC,the capacitance calculation i s given under type D voltage dip conditions.

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