Research And Design Of Quasi-single-stage Interleaved Flyback Grid-connected Micro-inverter

Photovoltaic grid-connected micro-inverters are widely used in household photovoltaics and small and medium-sized industrial and commercial photovoltaics due to their small size,light weight,good stability and high efficiency,which are the research trend of distributed photovoltaic power generation.Firstly,the advantages and disadvantages of the two topologies of isolated micro-inverters were analyzed,and the quasi-single-stage staggered flyback topology as the research basis of micro-inverters was chosen in this paper.Secondly,three working modes of the flyback inverter were analyzed and compared in detail.The peak current modulation strategy of the self-regulating working mode was proposed,and the specific formula of the working mode adjustment point was calculated.This strategy allows the flyback inverter to use different operating modes in different phase intervals of half a grid cycle,which can maximize the power density and improve the efficiency of inverter.Then,a resonant soft switching strategy was introduced to control the conduction of the flyback switching tube when the terminal voltage resonance decreases to zero,so that the loss of the flyback switch tube can be reduced to an acceptable range.At the same time,an improved MPPT algorithm was proposed to calculate the output power of photovoltaic modules without detecting the DC current,saving the design cost of the inverter hardware.For the software and hardware design of micro-inverter,a dual system control scheme was designed in this paper,which divides the whole micro-inverter system into primary side and secondary side parts.The two parts have different emphasis on control and operation,with clear division of labor,safety and reliability,and low operating and maintenance costs.In addition,topology design and device selection of each circuit module were given in terms of hardware,and also includes the calculation of important parameters of the main power circuit.In the aspect of software,the anti-islanding strategy and the working principle of software phase-locking were mainly studied.The active frequency-shifting anti-islanding strategy and the phase-locking algorithm based on d-q coordinate system were adopted.And the full-bridge inverter control algorithm and power line carrier communication algorithm were designed.Finally,a prototype of grid-connected micro-inverter with rated output power of 300 W was developed.Through the debugging and experiment,the test waveform of the above theory was given,and the effectiveness of the inverter hardware circuit and software algorithm was verified.