Research On Operation Control Strategy Of DC Microgrid

Owing to the advantages of cleaning and pollution-free,photovoltaic power generation has been widely used in distributed generation.Although photovoltaic raw materials almost have no cost,its development is still limited.This limitation is mainly due to unstable power output caused by the battery temperature and light intensity.Therefore,in order to balance the system power,the photovoltaic power generation system requires a certain capacity of energy storage devices.Because of the cost of the energy storage device is about 20%~25% of the cost of the PV power station,and the service life of energy storage is very short,how to solve the problem of energy storage is the key to improve the stability and the power quality of the photovoltaic system.Combined with the existing research results and the traditional energy storage method,this thesis proposes a new operation control strategy for the DC microgrid with super capacitor.First of all,this thesis introduces the principle of photovoltaic power generation system and builds its simulation model,Then,it analyzes the maximum power point tracking(MPPT)technology and constant voltage technology of PV power generation system,and compares these two commonly used MPPT method,namely the disturbance observation method and incremental conductance method.Secondly,the equivalent circuits and charge and discharge control circuits of the battery and the super capacitor are given in this thesis.Immediately,the main structure of the hybrid energy storage system is finalized and connects with the DC bus through the bidirectional DC / DC converter.Finally,according to voltage fluctuation of DC bus caused by unstable power output and load power mutation,a corresponding power allocation strategy is designed.Because the main purpose of this strategy is to stabilize the bus voltage by controlling the DC micro grid power balance,it can also be called the power allocation strategy.This strategy will play a role together with the operation mode of hybrid energy storage system under different voltage conditions.Through the control of the PWM signal of the unidirectional converter and the bidirectional converter under different operating modes,the control strategy can switch different modes automatically,thus achieving the purpose of coordinated control of energy flow.In this thesis,the virtual microgrid system including photovoltaic power generation unit,battery,super capacitor and load is built by simulation software Matlab / Simulink and to verify the effectiveness of the proposed method.The simulation results show that when the load is abrupt,the battery and the super capacitor are coordinated rapidly to restore the voltage,the DC bus voltage fluctuation is suppressed,and the system can be operated stably.