Research On AC Side Power Decoupling Of Distributed Photovoltaic Micro-Inverters

Easy expansion,modular design,high power generation,hot swap and low cost are the main advantages of micro-inverters,which makes micro-inverters the main development direction of future distributed PV inverters.Since the grid side power contains twice the power frequency pulsating power,this causes the bus voltage and the DC side current to generate secondary ripple,which affects the quality of the grid-connected current on the output side of the inverter and the stability of the DC side MPPT,resulting in DC side fuel.Battery and photovoltaic cell utilization is reduced.The common method is to solve this problem by connecting a large electrolytic capacitor in parallel with the photovoltaic module.However,the short life of the electrolytic capacitor seriously affects the service life of the inverter.This paper designs an exchange.The side power coupling topology,through the PEM control,absorbs the secondary pulsating power in the circuit,reduces the capacitance of the bus capacitor,thereby replacing the film capacitor of the longevity,and prolonging the overall service life of the micro-inverter.The power decoupling circuit is divided into four categories according to the structure or position of the power coupling topology: PV level,DC-link level,AC level decoupling and three-port decoupling.The technical characteristics of various methods are compared and analyzed.The principle of power coupling circuit is introduced.The input and output characteristics and power coupling dynamic characteristics of the coupling circuit are studied.The time domain and frequency domain relationship between the inverter and the coupling circuit are analyzed.The circuit structure and working mode of the designed AC side power electronic power coupling circuit are introduced.The small-signal model and PWM control strategy of the main circuit are studied,and the pulse width calculation method for different working modes of the decoupling circuit is analyzed.Using Matlab/Simulink 2015 b simulation software to simulate the proposed power decoupling topology,the simulation research of photovoltaic micro-inverter based on AC side parallel power decoupling is carried out.The simulation research under different working conditions is carried out.The results show that the decoupling circuit is When the load power is higher than 500 W,the influence on the grid-connected performance becomes smaller as the load power increases.The decoupling circuit has the best decoupling effect on the two-stage inverter before the load power is 500 W.At the same time,according to the simulation results,the four topologies are compared from the decoupling ability and the decoupling capacitor voltage.Compared with the four decoupling topologies,the single-mode six-switch Buck-Boost decoupling circuit has advantages in performance.The single-mode six-switch Buck-Boost decoupling circuit was selected for hardware experiment.The hardware platform design of the whole experimental platform and each component was introduced.The experimental results were summarized and analyzed.Finally,the hardware experiment results were consistent with the theoretical results.The power decoupling circuit suppresses the secondary ripple of the main circuit,and can replace the short-lived electrolytic capacitor with a long-life thin film capacitor to extend the overall life of the micro-inverter.