Research On Photovoltaic Grid-connected Module Integrated Flyback Converter

High power centralized converter and low power distributed converter (Module Integrated Converter, MIC) is the two major development directions of photovoltaic grid-connected converter technologies. Centralized converter adopts centralized MPPT, unable to overcome the non-uniformity caused by PV module installation and the differences of modules’characteristics, easily lead to system mismatch, reducing system efficiency. MIC, integrated with individual PV module, functioned by independent MPPT, has many advantages such as high generating efficiency, flexible expansion, plug-and-play, easy integration, etc., which result in its wide prospects in the BIPV/BAPV and other small power application.This paper focus on the Module Integrated flyback Converter, the principal research concentrates on the topology of the main circuit, the analysis and design of the high frequency soft switching circuit for its high efficiency, minute extension and high security. When the flyback converter works, it acts as both the role of the inductor to store energy, but also to achieve voltage conversion and electrical isolation. Duo to the parasitic of the oscillation of the leakage induction and switch, transformers, etc. the voltage of the drain-source will spikes high, which makes the switch voltage and current stress increase and large loss of the circuit.Select the ZCS quasi-resonant flyback converter as the main circuit structure because of the relatively simple structure and realizing the soft operation of a power switching device, and the energy of the magnetizing inductance and transformer leakage inductance can be fully utilized by the resonant effect. Through the converter principle and simulation analysis, the nonlinearity of the system deteriorated because of the resonance effect, leading to the influence of the energy transformation from the primary winding to the secondary winding. In order to overcome the non-linearity of the circuit, add an auxiliary switch which adopt synchronous rectification technology to eliminate system oscillations in the secondary winding on the basis of ZCS quasi-resonant flyback converter. When Change the main switching frequency under the mode of DCM, the nonlinear significantly improved which is verified by the simulations. A200W interleaved flyback PV MIC is manufactured, the input of the inverter uses two parallel flyback converter, which improves the system stability and efficiency. Experimental results show that, the interleaved flyback PV MIC has the characteristic of stable operating.