Research On Parallel Technology Of Ship DC Microgrid Multi-Converters Equivalent Current

With the continuous development of new energy power generation and power electronic devices,ship DC networking technology has been adopted by more and more ships.Due to the easy access to new energy power generation,the application of marine DC microgrid can reduce fossil energy consumption and solve the marine environmental pollution problem,on the other hand,it can improve the development rate and share of renewable energy in modern ship energy.Received widespread attention.This paper takes each unit converter in the ship's DC microgrid as the research object,and focuses on the precise power distribution and secondary regulation of the DC bus voltage when multiple converters in the energy storage unit are operated in parallel.The main research work is as follows:Firstly,based on the proposed ship's DC microgrid structure,mathematical models of photovoltaic power generation unit and battery energy storage unit were established respectively,and a photovoltaic power generation unit control strategy based on operating mode switching was designed to ensure that the DC microgrid operation mode can adaptive requires switching between two modes of maximum power tracking control and constant voltage control.At the same time,the battery energy storage unit uses a droop control strategy during charging and discharging to ensure the power balance of the DC microgrid.Secondly,in the traditional droop control,the presence of line impedance will not only cause uneven power distribution of the battery energy storage unit converter,but also cause voltage drop problems when the photovoltaic power generation unit and battery energy storage unit control the DC bus,so a method is proposed.The active detection method of line impedance based on low-frequency sinusoidal current injection solves the load of the energy storage unit converter caused by the line impedance of the converter by more accurately extracting the line impedance value of each unit in the system and then compensating the virtual impedance coefficient in the traditional droop control.Then,for the problem of bus voltage drop caused by virtual impedance,a secondary control strategy of DC bus based on voltage mean observer is proposed.The mean value observer is used to obtain the average value of the output voltage of the parallel converter,and this value is used as the secondary adjustment.The feedback of the voltage controller can effectively improve the bus voltage drop caused by the droop control,and maintain the DC bus voltage to work at the rated value.Finally,Matlab simulation experiments and dSPACE semi-physical verification are performed on the precise load distribution and secondary bus voltage regulation of the designed energy storage converter.The results show that compared with traditional droop control,a virtual impedance adjustment control strategy based on active detection of line impedance is implemented The load power sharing accuracy is high,and the low-speed communication DC bus voltage regulation strategy proposed in this paper can achieve the bus voltage stability at the system rated value.