Abstract
Recently, module integrated converters (MIC) have become a hot research topic as a means for overcoming the partial shading effects of PV systems. Also, for safety reason, an isolated version is adopted. In this thesis, in order to further improve the energy yield, emphasis is placed on the development of novel isolated ZVS AC module for PV systems. Major contributions of this thesis can be summarized as follows. First, a novel pseudo dc-link converter topology is proposed to achieve ZVS condition. It consists of an isolated voltage quadrupler DC converter cascaded with another full-bridge inverter operating under line frequency to achieve higher efficiency. Only two active switches and one capacitor are added to the interleaved controlled voltage quadrupler to achieve zero voltage switching. Second, a simple control strategy is proposed to generate a rectified sine waveform voltage at the dc-link ac capacitors. Unlike the control strategy in existing active clamped ZVS circuit where the auxiliary switches only act for a short time, in this thesis, the gating signal of auxiliary switches are just complementary to that of the active switches to achieve ZVS. In addition, merits of the voltage quadrupler such as automatic uniform current sharing capability, small ripples, and the low voltage stress of all switches as well as diodes can be preserved. Third, a prototype with 25V input, 110Vrms output and 300W rating is constructed for verifying the feasibility of the proposed AC module. Experimental results show that the overall efficiency of the AC module is higher than 87.5% as the load is varied from 50W to 300W, and the highest efficiency of 92.6% is achieved at 100W.