Research On T-type Three-phase Photovoltaic Grid-connected Inverter

In many multi-level inverter system topologies,T-type three-level inverter has been widely used in large-scale photovoltaic grid-connected system because of its low output harmonic content,low power consumption and low system cost.Therefore,in this paper,taking 20 k W T-type three-level inverter system as the background,the main topology parameters and control circuit of the system are designed.At the same time,an effective overall system control scheme is presented,and a new suppression method is proposed for the problem of PID effect in PV modules.In order to reduce the loss of the system and take into account the wide bus voltage range of the system,an improved Boost circuit is selected as the pre-level main topology of the T-type three-level inverter system.According to the design index of the system,the parameters of T-type inverter circuit and LC filter circuit are designed.At the same time,the detective and protective circuit of the system are designed too.In this paper,the working principle of T-type three-level grid-connected photovoltaic inverter system is analyzed and the mathematical model of the system is established.Be based on the double closed loops of voltage and current,the overall control strategy of the system is designed.This paper focuses on selecting parameters of the system voltage and current controller in order to avoid the difficulty of manual tuning of system controller parameters.Simulation and experimental results show that the inverter system can achieve better steady-state and dynamic performance if the voltage and current double closed-loop control scheme and this controller parameter are utilized.In high temperature,humid environment,Photovoltaic cell components are very prone to Potential Induced Degradation(PID)effect.In order to analyze the cause of the PID effect,the mathematical model of leakage current was introduced into the traditional PV module model.And a simulation model of PV module with PID effect is built to verify the PID effect caused by leakage current.The PID effect will cause the solar cell module to appear the black spot and the output power of PV module to decrease.In this paper,a new method is proposed to suppress the effect of the PID on the photovoltaic cell module.By raising the voltage of the PV-to ground,the leakage current path of PV cell components can be suppressed.It can achieve the purpose of suppressing the PID effect,when the leakage current path is suppressed.The proposed method has the advantages of strong universality and low demand on the system hardware.In addition,simulation and experimental results verify the feasibility of the proposed suppression method.