Research On Voltage Self-balancing Circuit And Control Technology Of Bipolar Dc Microgrid Source-side Converter

In recent years,environmental concerns and energy policies have driven a shift towards sustainable and distributed energy systems.As a popular architecture of DC microgrid,bipolar DC microgrid has more flexible output voltage and more stable system,and has been widely used in distributed microgrid.However,the imbalance of the bipolar DC microgrid loads and the source leads to the deterioration of the power quality of the bus,and in severe cases,damages the power devices and affects the stability and safety of the system.In order to ensure that the source-side converter is efficiently connected to the DC microgrid,the source-side converter needs to have the characteristics of high voltage gain and low ripple.At the same time,a controller with better anti-interference performance and robust performance is required to ensure that the source-side converter can stably track the voltage reference value and achieve effective regulation of the output voltage.Based on these,this thesis conducts research on the self-balancing circuit and its control technology of bipolar DC microgrid source-side converters.The main research contents are as follows.Firstly,in view of the requirement of voltage balance and high voltage gain in bipolar DC microgrid,this thesis proposes a source-side high-gain interleaved dual-outputs Boost converter from the perspective of topology,and analyzes the different working modes of the converter.The strategy of voltage and current sharing in negative current mode is expounded,and the loss analysis and small-signal modeling process are given.The single output voltage gain of the converter is twice that of the traditional Boost converter.The charge balance of the intermediate capacitor is used to realize the automatic balance of the two-phase branch currents corresponding to the same output,and the negative currents are used to eliminate the voltage imbalance problem caused by load mismatch.At the same time,all switches are guaranteed to achieve zero voltage switching（ZVS）,and the theoretical feasibility is verified through simulation and experiments.Secondly,aiming at the problem of voltage imbalance caused by inconsistent dead time,this thesis proposes a three-state switching input-parallel-output-series（IPOS）converter with dual outputs structure.The voltage unbalance mechanism of load mismatch and asymmetric dead time is expounded.The voltage balance strategy based on the volt-second balance of the inductor is analyzed,and the design requirements of the converter parameters are given.This converter generates a new working mode（threestate）by adding an auxiliary balance branch,and then realizes the purpose of indirectly adjusting the output voltage according to the inductor voltage.It has the characteristics of simple topology and easy adjustment,and has been verified by experiments.Finally,in the source-side dual-outputs converter topology structure composed of bipolar DC microgrid,photovoltaic power generation system and three-state switching IPOS converter,for ensuring that the source-side converter can stably track the voltage reference value and ensureing good anti-disturbance performance and robust performance,based on the disturbance observer（DOB）control and proportional integral（PI）control,a single-degree-of-freedom robust tracking control technology is proposed in this thesis.The topology structure of the source-side dual-outputs converter is introduced,the control design steps are described,the performance of the robust tracking control is analyzed,and the parameter setting basis is given.The robust tracking control has the characteristics of simple structure,strong portability,no need for accurate model,good anti-disturbance performance and robust performance,and has been verified by simulation.