Performance Analysis Of Three-level High Voltage Gain Bi-directional DC/DC Converter With Integrated Buck-boost

Adding energy storage modules to the DC micro-grid can improve the stability of the system and the utilization of renewable energy.A bidirectional DC/DC converter with high-voltage gain is needed to be connected between the energy storage medium and the DC bus since the voltage level of energy storage medium is low.Converter with high-voltage gain can be divided into isolated converter and non-isolated converter.Isolated converter can achieve high voltage gain when the secondary windings of transformer are relatively high to the primary windings,but this can result in poor coupling and large leakage inductance.Large leakage inductance will reduce system efficiency and increase voltage spike across the power tube.At the same time,bidirectional DC/DC converters are susceptible to instability of the system due to load characteristics under constant power loads.In order to achieve high voltage gain while avoiding the large leakage inductance of isolated converter,this paper presents an improved non-isolated bidirectional DC/DC converter with high-voltage gain.The operating mechanism of the proposed converter is analyzed.The relationship of voltage and current and the critical conditions of the continuous inductor current are obtained.In order to guarantee converter's good dynamic and static performance,the mathematical model of the converter is established and then design a double closed-loop regulator.A regulator of the flying capacitor voltage is designed which ensures the voltage balance of the power tube in the three-level bridge arm.For the situation where the system is instable under constant power load,the influence of line filter parameters load power and DC bus capacitance on the stability of the cascaded system is analyzed by the improved criterion of impedance ratio forbidden region.This paper carries out simulation verification through MATLAB/Simulink on the basis of theoretical analysis.Experimental prototype based on the control of DSP-F28335 and FPGA control is built,which verifies the correctness and feasibility of theoretical analysis.