Research On The Quasi-Z-source Inverter For Energy-stored System

In terms of power supply,as the main representative of renewable energy sources,photovoltaic or wind power is an effective way to deal with the fossil energy crisis and solve the environmental protection problems.Different from traditional power generation technology,renewable energy electricity transformation be achieved through the power electronics technology.Aiming at the eliminating the limitation of the existing converter topology,some scholars proposed a series of source impedance converter topologies.All of them can obtain wide range dc-link voltage,allowing bridge shoot-through,improve the quality of output waveform,which got more and more attention.This paper focuses on the Z source inverter,aimed at several key problems in its application,the concrete research content is as follows:1.The quasi-Z-source inverter features as the shoot-through capability.However,the protection mechanism for the shoot-through current is essential because of the increased current stress on the devices.This paper presents a shoot-through current sensing method for the protection by the combined currents.No extra hardware is added and the voltage spike is utterly avoided by integrating the stray inductor into the impendence network.Simulation and experimental results validate the performance of the proposed methods.2.Single-phase quasi-Z-source inverter secondary components analysis and its active suppression method.The second-order harmonic power flows into the do side of a single-phase quasi-Z-source inverter,which is harmful to the whole system.Generally large capacitor or LC resonance circuit is adopted to suppress the pulsating power,increasing the volume and weight of the system.Firstly the mechanism of second-order pulsation on the passive components of impedance network without active suppression method is analyzed.And then the passive components of the design process is given.In order to improve power density by reducing system capacitance and inductance,a novel and active method with paralleled auxiliary unit is proposed to suppress the second-order harmonic power.3.Energy stored quasi-Z-source inverter combines advantages of quasi-Z-source inverter and energy storage technology.It aims to reduce the power fluctuation in the PV and fuel cells systems.The dynamic regulation of the embedded energy storage units(battery or ultra-capacitor)is critical for the system performance.In this paper,the oscillation and overshoot in the dynamic process are analyzed with a full order system model.The low damping ratio issue related with the battery internal resistor is found to be the key obstacle for the improvement.The resulted bandwidth limitation on the conventional PI type current controller is explored mathematically.An enhancement is then proposed based on the active damping technique.The bandwidth is extended and better dynamic performance is achieved.