Because AC module system is directly connected to grid source, power pulsation is appeared at AC module input capacitor. So, it can adversely affect maximum power point tracking (MPPT) control. Furthermore, photovoltaic (PV) module power can be fluctuated with varying irradiation while constant load demand. To reduce power fluctuation for MPPT control and stabilize the PV system with varying conditions, conventional flyback converter has auxiliary circuits for active decoupling and energy storage system (ESS) is proposed for energy efficiency. Proposed AC module system can solve the above problem (i.e. power pulsation, varying irradiation and load demand) by auxiliary circuit operation. But when the proposed AC module system is operating, it has various modes according to power flowing. In this paper, analyzes proposed AC module of operating modes, which show perform the overall system operation. To confirming proposed AC module system, verified by PSIM simulation result.
In general, electrolytic capacitors are used to reduce power pulsations on PV-panels. However, this can reduce the reliability of the PV AC-module system, because electrolytic capacitors have a shorter lifetime than PV-panels. In addition, PV-panels generate irregular power and inject it into the grid because the output power of a PV-panel depends on the surrounding conditions such as irradiation and temperature. To solve these problems, a grid-connected photovoltaic (PV) AC-module with active power decoupling and energy storage is proposed. A parallel bi-directional converter is connected to the AC module to reduce the output power pulsations of PV-panels. Thus, the electrolytic capacitor can be replaced with a film capacitor. In addition, the irregular output power due to the surrounding conditions can be regulated by using a parallel energy storage circuit. To maintain the discontinuous conduction mode at low irradiation, the frequency control method is adopted. The design method of the proposed converter and the operation principles are introduced. An experimental prototype rated at 125W was built to verify the performance of the proposed converter.
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