Research On Photovoltaic Power Generation Inverter Based On Series Power Decoupling

The inverter in a PV power generation system plays an important role in connecting the grid to the PV system.When the PV inverter is connected to the grid,the output power on its AC side should meet the requirements of grid-connected operation,which will cause an imbalance of power on the AC/DC side of the inverter,and this phenomenon will cause unnecessary two-fold ripple pulsation on the DC side of the inverter,reducing the utilisation of the DC input source of the inverter.The conventional solution is to connect a large electrolytic capacitor in parallel on the DC or AC side of the inverter.While this approach is simple and feasible,the life span of the electrolytic capacitor is relatively short,which indirectly affects the service life of the PV inverter.To solve this problem,this thesis investigates the power decoupling problem of PV inverters and proposes the use of an active power decoupling circuit to eliminate the dc-side double frequency pulsation problem of the inverter.In order to solve the problems of low utilisation rate and short service life of electrolytic capacitors in the traditional power decoupling technology,it is proposed that the electrolytic capacitors and IGBT tubes are used together to form an additional power decoupling circuit to replace the large electrolytic capacitors for power decoupling.Through the analysis and comparison of different power decoupling solutions,a series power decoupling circuit is suggested as the main research method;for the characteristics of open-loop and closed-loop control methods,the inductive current closed-loop control method of closed-loop direct control is selected to control the pre-stage decoupling circuit.Based on the control principle of series power decoupling circuit,a small-signal model of the circuit is established and the control strategy for the decoupling circuit as well as the circuit parameters are designed;based on the phase-locked loop technique of second-order generalized integration and the voltage current double closed-loop control strategy,the stable control of the back-stage inverter circuit is achieved so that it can operate efficiently.Finally,according to the adopted series power decoupling inverter and its control strategy,the hardware circuit and software flowchart are designed and the simulation model is built on Matlab platform,while some relevant experiments are conducted to further verify the feasibility of the series power decoupling circuit.The simulation and experimental results show that the series power decoupling inverter and its control strategy can compensate the unbalanced power on the AC and DC sides of the inverter and suppress the secondary ripple pulsation of the DC side current.Figure [49] table [1] reference [80]...