Research On The Control Technique Of The PV-Battery Inverter In The Diesel-PV-Battery Shipboard AC Microgrid System

When applying solar energy to new energy ships,there are problems such as the limited laying area,the intermittent power supply,and the low power conversion efficiency.It is necessary to add energy storage devices and combine them with traditional fossil energy.The diesel-PV-battery shipboard AC microgrid system formed is more suitable for the developing trend of the ship power system.The capacity of the ship power system is limited,and the large-scale fluctuation of the ship microgrid voltage and frequency caused by the high-power electric propulsion load affects the stable operation of the PV-battery inverter,it is essential for the PV-battery inverter to affect the stable operation of the diesel-PV-battery shipboard AC microgrid system.This paper focuses on the stability analysis of the control technique of the PV-battery inverter in the diesel-PV-battery shipboard AC microgrid system in three parts as following:the design of the control system,the effect of the shipboard microgrid system to the stability of the PV-battery inverter,and the improvement of the microgrid system stability.The stability design of the PV-battery inverter,used in the shipboard power system,needs to be considered primarily.This paper studies the parameter design method of the PV-battery inverter control system based on droop control.The mathematical model of LCL three-phase PV-battery inverter is established.After comparing and studying the three control strategies of constant power control,constant voltage and constant frequency control and droop control,the parameter design of the voltage,current controller and power loop controller used in the droop control is carried out,and the parameters are verified the correctness of the design by simulation experiments.When serious power quality such as frequency oscillation or harmonic pollution occurs in the ship power system,the ship power system has three-phase unbalance,low-order harmonics,DC bias,and large transient fluctuations in voltage and frequency when the load changes suddenly.This paper proposes a SOGI(Second-order Generalized Integrator)based on the phase-locking problem of the AC bus voltage on the PV-battery inverter.SOGI-FDE-FLL(SOGI-based Structure with prefilter,a dc-offset block,a positive sequence extractor,and frequency-locked loop)of the diesel-PV-battery shipboard AC microgrid system accurate tracking,as well as the elimination of DC bias and the extraction of positive sequence components,the optimal design method of circuit parameters is obtained.The experimental results verify that the proposed phase-locked circuit structure has an excellent phase-locking effect under poor power quality and deplorable conditions phase.The stability mechanism and its improvement method of the diesel-PV-battery shipboard AC microgrid system with the PV-battery inverter connected to the grid are studied.The stabilizing influence of the LCL resonant in the PV-battery inverter is analyzed,obtaining parameters optimization design.The equivalent load model of the marine electric propulsion system is established.Then,the equivalent impedance model of the microgrid system is obtained.Moreover,the negative impedance characteristics of the constant power load are studied by the system impedance characteristics,which reduces the system damping and system stability.In the end,the external virtual impedance changes the equivalent impedance on the load side,offsets the negative impedance characteristic of the constant power load,and obtains a method for improving the stability of the diesel-PV-battery shipboard AC microgrid system.