Research On New Z-source Inverter In Photovoltaic Grid-connected System

In recent years,Distributed generation system in the application of life provide a good platform for solar applications in power systems.And the photovoltaic(pv)grid inverter has played a key role in the photovoltaic system.Single-phase photovoltaic(pv)grid inverter are studied in the topic.The advantages and disadvantages of the original Z source pv systems are analyzed,and proposes a new type of Z source-quasi-Z source pv systems.The topic put forward the corresponding methods of maximum power point tracking and set up the hardware platform.Through the simulation experiments show that the inverter can achieve maximum power point tracking of solar panels.The inverter output current can be accurately to real-time tracking of power grid voltage.The design also has the function of island detection and protection.First,the principle of the topological structure?the working state and small signal model of quasi-Z source is introduced in this paper,and the advantages of quasi-Z source topology is proved.In this paper the inductance and capacitance parameters in the quasi-Z source topology are designed;According to the requirements of the output,LCL output filter is applied to the quasi-Z source photovoltaic inverter system creatively,controlling the high frequency harmonic of power grid.It guarantees the quality of the output power.Second,detailed analysis for the control strategy of quasi-Z source inverter are made in this paper.It uses the single polarity PWM modulation method.The direct state is inserted into the PWM zero state.That achieve the goal of the booster;the paper proposes basing on a modified variable step conductance increment method to control direct duty ratio and achieves the maximum power point tracking;This article uses the voltage and current double loop control strategy.PI controller is adopted to control the active duty ratio.That implements that the inverter output current and the grid voltage are the same in frequency and phase.Again,the design of inverter island detection function is introduced in this paper,and is used to design the periodic tests to detect islanding,the different types of load conditions.A lonely island detecting time and the change of the output frequency.Implements the islands of the functions of detection and protection.In this paper,the corresponding hardware and software design are made for the control system.By selecting STM32F407 control chip and its peripheral circuit,the signal acquisition and signal communication of power grid voltage and output current is realized,and the modulation wave and direct duty ratio is generated to control the output of IGBT drive signal.Finally,quasi-Z source inverter system simulation model is set up and the system output current?power grid voltage and current harmonic distortion rate has carried on the analysis and simulation.The design realizes that the output current and power grid voltage are the same in frequency and phase and success on the higher harmonic suppression.