Research On Three-Port Flyback Inverters With Power Decoupling

With the modularization of solar power generation devices, photovoltaic(PV) power generation becomes the most popular one. the key link PV inverter based on high reliability, long lifespan and low cost is studied deeply. This thesis is dedicated to the three-port flyback inverters with power decoupling.When the PV inverters output ac voltage, the input power of PV inverters should be constant to realize the maximum power point tracking(MPPT). Large electrolytic capacitors are usually placed at the dc bus of inverters or the output of PV modules to maintain the input power and output power balance. But the electrolytic capacitor has disadvantages, such as large volume, low reliability and short lifespan, which limit the lifetime of the inverters. So electrolytic capacitors should be removed. In this thesis, the operation principle of a single phase flyback inverter with ripple port is analyzed, and the control method of the first-stage flyback converter is discussed in detail. The inverter realizes input dc power and output ac power while the ripple port decouples power ripple, which is verified by simulation.The power devices in the ripple port of the above inverter are more and the currents in the inverter are controlled by closed-loop which is complex. So, a novel three-port flyback inverter with power decoupling based on the above inverter is proposed. An auxiliary circuit is introduced at the transformer primary side in order to let the power ripple with twice the line frequency flow. Consequently, the input current of the proposed inverter is a pure constant dc current and the power ripple decoupling is realized. The relationship between the auxiliary capacitor's voltage ripple and its capacitance is discussed, and other key parameters are also designed.Based on the theoretical analysis, a 100 W prototype has been built and tested in the lab. The experimental results are presented to verify the feasibility of the proposed flyback inverter.