| The “carbon peak” and “carbon neutral” development goals are effective ways to deal with the two major problems of energy shortage and climate change,and are conducive to building a green,low-carbon and sustainable circular economy.Renewable energy power generation has the advantage of being clean and pollutionfree,and it is an important carrier for building a green circular economy.Among many renewable energy power generation,photovoltaic(PV)power generation has unique advantages such as safety and reliability,wide distribution area,and short construction period,occupying a dominant position.As the interface between PV panels and grid,grid-connected inverter is an indispensable key equipment in PV power generation system.Its efficiency,cost and safety have always been the research hotspots of many scholars.This paper starts from two aspects of single-phase PV grid-connected inverter topology and control technology,and makes an in-depth and detailed research on the leakage current suppression of single-phase non-isolated PV grid-connected inverter,the optimization of input inductance of current source inverter(CSI),and the harmonic peak suppression of traditional sinusoidal pulse width modulation(SPWM)technology,and puts forward the corresponding solutions.It provides theoretical and technical guidance for the safe and reliable operation,cost reduction and efficiency increase of single-phase multi-level PV power generation system.This dissertation is funded by the National Natural Science Foundation of China(NSFC)project “Research on high power electro acoustic high efficiency energy conversion mechanism and control method” [51837005],the NSFC project “Research on topology,passive current sharing mechanism and control technology of coupled resonant network type multi-channel resonant converter” [51977069],the Program for Guangdong Introducing Innovative and Enterpreneurial Teams [2017ZT07G237] and Hunan Province “Revealing the List and Taking Command” project “Research on key technology of high-precision power supply system for key semiconductor process equipment” [2021GK1120].With the support of National Energy Conversion and Control Engineering Technology Research Center.This paper focuses on the leakage current suppression of single-phase non-isolated PV grid connected inverter,the input inductance optimization of current source inverter and harmonic peak suppression of traditional sinusoidal pulse width modulation technology are studied.The main work and innovations are as follows:(1)A single-phase I-type five-level PV grid-connected inverter topology and control strategy are proposed to suppress the leakage current in non-isolated PV gridconnected inverter system.Firstly,the mathematical model of leakage current of single-phase grid-connected inverter is established,and the relevant factors affecting the leakage current and the effective methods to suppress the leakage current are explored.Secondly,a I-type five-level inverter topology is proposed based on the leakage current model.Its working mode is analyzed in detail,the mechanism of the inverter to keep the common mode voltage constant is clarified,and a pulse width modulation strategy combining carrier-layer and phase-shifting is proposed with the constraint of the real-time balance of capacitor voltage.Then,the key characteristics such as stress and loss distribution of switching devices are comprehensively analyzed,the design method of flying capacitor is given,and a comprehensively comparison with the existing similar topologies is made.Finally,simulation and experimental verification are carried out.The results show that the proposed topology can effectively suppress the leakage current to 29.5 m A,which complies with the VDE-0126-1-1 gridconnected standard for PV inverters.(2)A single-phase full-bridge five-level inverter topology with leakage current suppression ability and control strategy are proposed to solve the problem that the traditional full-bridge five-level grid-connected inverter is difficult to meet the requirements of grid connection due to the large leakage current.Firstly,the composition of the traditional full-bridge five-level inverter topology is analyzed,and the reason why it can not effectively suppress the leakage current is revealed.Secondly,the topology deduction is carried out based on the flying-capacitor-clamped full-bridge five-level inverter,and a new full-bridge single-phase non-isolated five-level inverter topology with leakage current suppression ability is proposed.Its working modes are analyzed,the common mode equivalent circuit based on the junction capacitance of switching devices is established,and it is proved that the common mode voltage can remain constant in all working modes.Then,the grid-connected current control strategy,flying capacitor voltage balance control strategy and fault protection strategy are designed.At the same time,the proposed topology is compared with some existing topologies in terms of device stress,device loss and other key performance.Finally,the experimental results show that the proposed topology has excellent differential mode and common mode performance.(3)A single-phase single-stage CSI topology with buck-boost capability is proposed to solve the problem that the input inductance of traditional single-phase CSI is large and the input current is difficult to maintain balance.Firstly,the equivalent model of converter based on single inductor is established,the essential relationship between voltage source inverter and CSI is clarified,and the reason why the input inductor of CSI is large and the input current is difficult to maintain balance is revealed.Secondly,the topology deduction is carried out based on the equivalent model,and a single-phase single-stage CSI with buck-boost capability is proposed.The mechanism of seamless switching between topology operating mode and buck-boost mode is analyzed,and modulation and control methods are proposed.Then,the stress and system loss of switching devices are analyzed,and the parameter design method of DC input inductance and output filter capacitor is summarized.Finally,simulation and experimental verification are carried out.The results show that the proposed topology can not only reduce the DC input inductance,but also has the capability of buck-boost,which is very suitable for applications with a wide voltage input range such as PV power generation.(4)A passive variable switching frequency sinusoidal pulse width modulation(PVSFSPWM)technology is proposed to solve the problems of high harmonic peak value and serious electromagnetic interference(EMI)in the traditional constant switching frequency sinusoidal pulse width modulation(CSFSPWM)technology.Firstly,the basic principles of PVSFSPWM technology are introduced,and the mathematical method is used to prove that PVSFSPWM technology can obtain the same duty cycle as traditional CSFSPWM technology.Secondly,the mathematical analytical solution of the harmonic spectrum of the PVSFSPWM technology based on the double Fourier series is derived,the harmonic spectrum distribution law of the proposed method is explored,and the reason for the reduction of the harmonic peak value is revealed.At the same time,the performance of PVSFSPWM technology and traditional CSFSPWM method in terms of device loss and inductor ripple are compared.Then,for different microcontrollers,the digital implementation method of PVSFSPWM technology is proposed.Finally,the simulation and experimental verification are carried out.The results show that the PVSFSPWM technology is easy to implement in the microcontroller,and under the same inductor ripple current requirements,the PVSFSPWM technology reduces the inductance by 22.5% compared with the traditional CSFSPWM method,and the efficiency can be improved by 0.36%.The cost reduction and efficiency increase of the system are realized. |
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