| In order to fully absorb renewable energy,photovoltaic microgrid is formed by combining photovoltaic source,energy storage and load.However,in the photovoltaic microgrid,there is a frequency fluctuation problem caused by the imbalance of power supply and demand in different time scenarios,which seriously affects the power quality of the photovoltaic microgrid.In order to effectively eliminate the frequency fluctuation of photovoltaic microgrid and ensure its safe and stable operation,this paper studies the frequency control of photovoltaic microgrid,which has theoretical significance and application value.Firstly,the factors that affect the frequency fluctuation of photovoltaic microgrid are deeply analyzed,and the theoretical basis of the slow dynamic response time in the traditional droop frequency control system is given,that is,the moment of inertia and damping coefficient seriously affect the frequency oscillation of the system and the slow response time in the transient process.Based on the differential regulation control theory and the current frequency differential regulation method of microgrid,an improved differential frequency regulation method based on moment of inertia and damping coefficient is proposed.In this method,the mechanical power equation of power system prime mover is introduced into the rotor equation of virtual synchronous generator,and the mathematical models of frequency deviation and active power deviation are derived based on Laplace transform,The dynamic response speed of the system is improved by adjusting the damping coefficient;At the same time,the moment of inertia is adjusted to suppress the frequency oscillation of the system.Finally,the simulation results show that the improved differential regulation method can quickly increase the transient response time of the system.Secondly,in order to further eliminate the frequency deviation of photovoltaic microgrid,the source of frequency deviation is qualitatively analyzed with the help of graph analysis theory.Based on the improved differential control method and the traditional power system secondary frequency regulation technology,a frequency regulation method is proposed to realize the frequency adaptive control of photovoltaic microgrid by adding the active power compensation inertia link into the power frequency control loop of the improved differential control method.This method will improve the power value in the rotor motion equation of the virtual synchronous generator into the success rate deviation value,and at the same time,The improved equation combines the load increment of traditional power system with the active power output relation of virtual synchronous generator,and obtains the sum relation through theoretical derivation.Based on the relationship between the frequency and the constraints,the frequency deviation of the system tends to zero after a short transient process.Finally,the simulation results show that the frequency adaptive strategy can eliminate the frequency deviation and realize the frequency adjustment without error.Finally,a simulation model is built in matlabgsimulink to verify the frequency control method of microgrid with photovoltaic source.By comparing and analyzing the dynamic time response diagram of frequency,the simulation verifies the rapidity of the improved differential frequency regulation compared with the traditional frequency regulation.By comparing and analyzing the dynamic time response and frequency deviation response of frequency,the simulation verifies the rapidity and effectiveness of no difference frequency regulation compared with the improved difference frequency regulation. |
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