Abstract
The micro-inverter has attracted a great deal of attention in PV systems since it offers a superior solution for the shading problem in wide spreading of AC module technology, where each PV module has its own power conditioner. The micro-inverter is implemented from two-stages: DC-DC conversion and DC-AC conversion. This paper focuses on the first-stage of the micro-inverter including its high-gain and maximum power point tracking (MPPT). To achieve these features, an efficient MPPT algorithm is proposed for the LLC resonant-converter. Resonant converters are very promising topologies, due to their inherent features such as high-efficiency and very high-switching-frequency operation. Consequently, they have a small footprint and low switching losses due to zero-voltage-switching (ZVS) operation. To include resonant converters in PV applications, MPPT control is applied. Due to the non-symmetrical operation nature of resonant converters and pulse width modulated converters, the traditional MPPT techniques found in the literature are not suitable for direct application to the resonant converters. They need to be well-tuned before application to a resonant converter. To ease the usage of resonant converters in PV applications, this paper develops a novel phase-shift fixed-frequency MPPT algorithm that is compatible with the LLC resonant converter. It also reduces the EMI when compared to variable-frequency modulation due to the use of ZVS and a fixed frequency. The proposed MPPT technique achieves good performance, high steady-state efficiency and good dynamic response. The complete design procedure and analysis for the proposed MPPT phase-shift algorithm are presented in this paper. Finally, the presented system is validated based on PSIM simulations and hardware implementation on a 300-W prototype.