Research On Single-phase Non-isolated Step-up Photovoltaic Inverter

Energy is an important cornerstone for promoting national economic development,energy security will directly affect social stability and sustainable development.With the process of building a socialist modern country,China’s total energy consumption has been at the leading level in the world,and with the increasing expansion of economic growth,the constraints of energy on China’s economic development have followed,such as unreasonable energy structure,relatively insufficient supply and serious environmental pollution.Based on such setting,generating electricity technology by using clean energy such as solar energy has been used extensively.As one of the important interface equipment in photovoltaic system,PV inverter has also attracted the in-depth research of many scholars in the world.Hence,the study of inverter suitable for photovoltaic power generation is of graet significance for the efficient utilization of photovoltaic energy.Normally,the output voltage of PV cells are low.To obtain higher voltage,multiple batteries need to be connected in series,and then supply power to AC load or connected to the grid through inverter.However,the series batteries are easily interfered by shadow occlusion,which reduces systemic efficiency and dependability.For solving the problems,the DC-DC converter with boost capability can be cascaded with the full bridge inverter.This structure can easily boost the DC side voltage source and then realize the function of power inverter,and the two-stage circuit can be controlled independently.However,the traditional two-stage boost inverter uses a large number of power devices and high cost.If large capacitance is not used for decoupling,there will be cascade stability problems.Aiming at the shortcomings of two-stage boost inverter,this paper first proposes a non-isolated Step-up photovoltaic inverter(ISPI).This topology integrates each bridge of the traditional full bridge inverter with the DC boost converter,realizes the function of boost inverter,reduces the number of devices and improves the power density.For the proposed inverter,five modulation methods are further compared and studied,the characteristics of various modulation methods are summarized,and the working principle and steady-state characteristics of the proposed ILPI are analyzed in detail.Considering that the leakage current of general photovoltaic panels to the ground is generated to varying degrees,a non-isolated non-leakage current step-up photovoltaic inverter(ILSPI)is further proposed.The inverter uses fewer active power devices and suppresses the leakage current problem,which is conducive to improving the system efficiency and saving the cost,The security performance of the system has been strengthened.The working principle and steady-state characteristics,common mode current and the loss of switching devices of the proposed ILSPI are analyzed in detail,and finally compared with the PV inverters with similar functions.For the proposed ILSPI,a direct power grid-connection control strategy with maximum power point tracking function is studied.The corresponding simulation model is constructed,and the simulation verification is carried out for a variety of working environments.The results proved good performance of the control strategy.Finally,the main circuit,sampling and control circuit of the proposed inverter are designed.The experimental prototype of the corresponding inverters are built with TMS320F2812 as the core controller,the experimental results verifed the correctness of the theoretical analysis.