Research On Power Distribution Strategy Of Photovoltaic System For Solar Hybrid Electric Ship

Recently,in response to the energy crisis and resolve the problem of ocean environmental pollution,the development and application of renewable energy such as solar energy and hydrogen energy in ships have been gradually increasing.Meanwhile,ship’s DC microgrid technology has gradually become future a key research direction in the field of shipping power due to its advantages of energy saving,high reliability,and maximum acceptance of renewable energy.This thesis takes multiple parallel photovoltaic(PV)units in the solar hybrid electric ship DC microgrid as the study subject,aiming at resolving the transient fluctuation due to PV converter operating mode switching and the uneven power distribution of parallel PV converters in the constant voltage mode.The main research contents are as following:Firstly,on the basis of constructing the mathematical model of solar hybrid power ship PV-storage DC microgrid,aiming at the problem of bus voltage fluctuation greatly caused by the switching of working modes during the the PV unit operating,a novel smooth switching control strategy based on dp/di control is designed.This strategy uses the differential of the output real-time power p of the PV cell to the output current i as the control variable,and the switching of the PV unit working mode can be completed by tracking the different dp/di values of the PV cell.The Maximum Power Point Tracking(MPPT)and Constant Voltage Droop(CVD)modes are unified in the sense of using the same control loop,which avoids the hard switching between the two control modes,and effectively solves the problem of unstable bus voltage during the switching transient process.Then,aiming at the problem of low power distribution accuracy caused by multiple PV converters due to line impedance differences in CVD mode,an adaptive power distribution strategy based on dynamic consistency is proposed.This strategy adds a secondary regulation loop on the basis of traditional droop control,and dynamically changes the droop coefficient by constructing a γ function containing the output power of the PV unit and the output current of the converter in the loop,which eliminating the influence of the inconsistent line impedance on the power distribution accuracy.This strategy improves the accuracy of power distribution and realizes self-adaptive regulation of load power.In addition,in order to reduce the communication pressure of the system,the adjacent communication network architecture is constructed,and the dynamic average consensus algorithm is used to obtain the global average information and make it converge stably.Finally,Matlab/Simulink simulation and Hardware-In-the-Loop experiments are carried out to verify the proposed smooth switching control method for PV unit operating mode and the adaptive power distribution strategy based on dynamic consistency.The results show that the proposed control method effectively realizes the smooth switching of PV converter between MPPT and CVD modes,and its transient performance is significantly better than the traditional switching control method.At the same time,different PV converters have high power distribution accuracy in CVD mode.