Research On Nine Switch Converter Based On Photovoltaic Storage System

With the proposal of the strategic goal of "carbon to peak and carbon neutral" energy in China,it is urgent to promote clean and renewable energy to replace traditional fossil energy.As a representative of clean energy,photovoltaic power generation has been widely concerned and applied.However,photovoltaic power generation has the characteristics of randomness and volatility,and its output is difficult to ensure stability.By connecting to the hybrid energy storage system,the power fluctuations in the photovoltaic power generation process can be effectively suppressed,and the power quality requirements of the load and the grid can be met.On this basis,a nine switch converter is introduced to replace the original grid connected structure of the optical storage system to simplify multiple switch devices in the traditional structure.Firstly,the application scenarios and structural characteristics of nine switch converter are introduced.On this basis,its mathematical model and SPWM modulation mode are studied.In order to effectively solve the problem of low voltage utilization,a zero sequence modulation method of injecting triple frequency harmonic into modulation wave is proposed.The validity of the third harmonic immission mean is proved by simulation.It provides a theoretical basis for further research on the application of nine switch converter in optical storage system.Secondly,on account of the engineering mathematic pattern of photovoltaic cells,the universal simulation pattern of photovoltaic cells is established,and its external characteristics are simulated.Disturbance observation method is chosen as the maximum power tracking control technology.In the light of deducing and researching the mathematic pattern and control theory of photovoltaic grid connected inverter,it is proposed to realize the photovoltaic inverter grid connected function by using the upper channel of nine switch converter,and the simulation consequences are given.The simulation pattern of nine switches type in photovoltaic grid connected power generation construction is established.Finally,about the hybrid energy storage system,analyzing the working theory of super capacitor and Lithium iron phosphate battery.The equivalent circuit pattern is confirmed,and the emulation patterns of two categories of energy storage media are established to study their working characteristics.The energy storage system employs super capacitor-two-stage lithium iron phosphate battery structure.Each energy storage unit exchanges energy with photovoltaic power generation system through the lower channel of nine switch converter.The power of the energy storage component is allocated by a first-order low-pass filter,which takes full advantage of the complementary advantages of lithium battery energy storage and super capacitor,and effectively suppresses the power fluctuation of the photovoltaic system when the illumination changes.The simulation results show that the hybrid energy storage control strategy can optimize the distribution of the target power value,effectively reduce the number of battery charging and discharging,prolong the service life of battery energy storage,and at the same time,it can play a good role in stabilizing the power fluctuation.