High Reliability Research Of Micro-inverter Based On High Frequency Decoupling

In the new energy, solar energy is one of outstanding options, in centralizedphotovoltaic power generation, the efficiency of solar energy conversion to electricityhas been not high, because solar panels influences each other. Then the concept ofmicro-inverter is presented, which connected of single solar panels. Micro-inverter canwell solve the problem of interacting with each other in centralized photovoltaic solarcells, as result every solar cell can work on the maximum power point. At the same timethe work environment of micro-inverter is more flexible, especially suitable for city,community, etc.The life of solar cell is generally as long as twenty-five years, so the life of themicro inverter also needed to match with the life of the solar cell. Among the wholemicro inverter components, electrolytic capacitor is one of the main factors affecting theservice life of the whole system. While the capacitance is the requisite element of powerdecoupling in micro-inverter. According to the place in the micro-inverter topology ofpower decoupling, micro-inverter have three decoupling methods, namely solar outputpower decoupling, dc bus power decoupling and the third port power decoupling. Thethird port power decoupling is independent of the micro inverter input and output, andthe capacity value is also small, so get the latest research.This paper adopts a single-phase photovoltaic inverter topology with a series–connected energy buffer, in this topology we use the method of three port powerdecoupling, namely energy buffer independent with the input and output of inverter,such that the influence on micro inverter input and output is small; At the same time,thevoltage on both ends of power decoupling capacitor is higher, so the need capacitancevalue for power decoupling decreases, and use of film capacitor, improving the workingreliability and longevity of the micro-inverter. The next stage research the wholetopology control strategy. According to the principle of the basic circuit, get the controlstrategy of energy buffer circuit and cycloconverter circuit, namely phase shift controlrelative to the harmonic current; At the same time, get the equivalent impedance ofenergy buffer and cycloconverter during one period of grid. According to the equivalentimpedance of later stage, calculate the full bridge output impedance and the controlstrategy during one period of grid. In the micro-inverter topology control strategy, all ofthe duty ratio of switch is50%and switching frequency is fixed value, That remove theproblem of filtering brought by the frequency conversion control etc. According tobackward and preceding stage impedance matching and series LC series resonancefrequency calculated parameters and the transformer turns ratio.When use the improved disturbance observation (P&Q) to track the maximum power point of micro-inverter, which use of the difference of solar cell output power asthe error signal, through a proportional integral (PI) controller to generate appropriateperturbation step, ensure that can rapidly track the maximum power point of solar cell,and make sure not shock in the maximum power point. For the topology, adoptsadaptive enhancement phase locked loop (Adaptive-EPLL), make the phase differencebetween input and output is zero, at the same time when the time of start and power gridphase jump, by adjusting the parameters, to ensure the frequency will not jump,improve the reliability of the phase locked loop.This paper was proved by simulation and experiment to verify the accuracy of thewhole topology control strategy, implementation run under100W.