High-gain Multilevel Photovoltaic Inverter Based On Switched-capacitor And Hybrid PWM

With the growing maturity of the photovoltaic power generation market,research on inverters with higher performance is of great significance for the promotion,application and development of photovoltaic power generation systems.Multilevel inverters have gradually become the mainstream topology in photovoltaic inverters due to their advantages of higher conversion efficiency and lower output harmonics.Compared with other multilevel inverters,the unique advantage of multilevel inverters based on switched-capacitors is that they have independent boost capability and do not contain magnetic components.In particular,the multilevel circuits based on series-parallel switched-capacitors can make the system structure flexible and have the ability to automatically balance the capacitor voltage.Therefore,the introduction of switched-capacitor-based multilevel technology into photovoltaic inverters will help promote the innovation and development of photovoltaic power generation technology.In this thesis,after carefully summarizing and analyzing the advantages and disadvantages of the existing switched-capacitor-based multilevel inverters at home and abroad,a variety of switched-capacitor units are proposed.At the same time,they are combined with two half-bridge circuits to develop a series of novel multilevel inverter circuits based on switched-capacitors.Compared with the existing topologies,the proposed topologies in this thesis have a simple and flexible topology,strong independent boost capability,lower system cost and better output characteristics.This thesis mainly studies and verifies the proposed topologies from the aspects of topology structure,working principle,modulation strategy,parameter calculation,simulation and experiment.The specific contents are as follows:（1）Four switched-capacitor units are combined with the half-bridge circuits,and three thirteen-level inverters based on switched-capacitors are proposed.Three thirteen-level inverters are compared and analyzed in terms of topology structure,and their working principles are introduced in detail.For the special symmetrical structure of the circuit,the voltage ripple of the capacitor can be greatly optimized by using hybrid PWM strategy.The current spikes in the capacitors during charging and the power loss in the three topologies are carefully analyzed.Finally,this thesis builds a simulation model and an experimental prototype to verify the correctness of the theoretical analysis and the feasibility of practical application of the proposed thirteen-level inverters.（2）By improving the switched-capacitor units,two nineteen-level inverters based on switched-capacitors are proposed.The two nineteen-level inverters are compared and analyzed in terms of topology and working principle.Two extended structures of the nineteen-level inverters are proposed,which further expands the number of output levels and improves the boost gain.Based on the hybrid PWM strategy,one of the topologies is analyzed in detail from four aspects: modulation principle,capacitor voltage balance,capacitor voltage ripple and power loss.Finally,the correctness of the theoretical analysis and the feasibility of practical application of the proposed nineteen-level inverter are verified in simulation and experiment,respectively.（3）A single-phase photovoltaic grid-connected simulation system is built with the thirteen-level inverter as the main topology of the inverter link.The structure of the single-phase photovoltaic grid-connected system is introduced from the main circuit and the control circuit.The input power control principle based on maximum power point tracking（MPPT）and the grid-side current control principle based on proportional resonant（PR）regulator are analyzed in detail.Finally,the feasibility of applying the switched-capacitor-based thirteen-level inverter in the photovoltaic grid-connected system is verified in the simulation.