| Due to the global energy shortage and the aggravation of environmental pollution,countries began to focus on the development of clean renewable energy,so wind power,photovoltaic power,electric vehicles and other pollution-free power supply or equipment developed rapidly and popularized;At the same time,in order to reduce the pollution and investment cost of power system i n frequency modulation,demand side frequency modulation technology also arises at the historic moment.However,the fluctuation and intermittence of the outpu t power of wind power generation and photovoltaic power generation have a great impact on the power quality when they are connected to the power grid.As an important system for absorbing wind power and photovoltaic power generation,microgrid has gradually attracted people’s attention.As one of the future power development directions,the island microgrid contains more power electronic devices,wind power generation and photovoltaic power generation whose output is affected by environmental factors,and lacks the support of large power grid,resulting in poor frequency modulation ability and frequency stability of island microgrid.Therefore,it is necessary to combine the power side and demand side to study the frequency modulation control strategy of islanded microgrid.Firstly,the V/F control,PQ control and droop control models of microgrid under different operation modes are analyzed and established;Aiming at photovoltaic power generation,an accurate photovoltaic cell model for its engineering application is established,and a variable step perturbation and observation(P&O)method is proposed to track the maximum power point of photovoltaic array.On this basis,a three-phase photovoltaic power generation model is established,and the voltage,current and frequency fluctuations are analyzed;Establish the doubly fed induction wind turbine(DFIG)model.The stator side of the DFIG back-to-back converter adopts grid voltage vector control,and the rotor side adopts the stator voltage vector control method to control the DFIG output constant voltage and constant frequency.The diesel generator model is established to ensure the operation of island microgrid in extreme weather environment.Secondly,based on the daily life of a community with 1000 househo lds,analyze the basic parameters,travel habits and other factors of the community’s electric private cars,electric buses and electric taxis that affect its mathematical model.Based on the Monte Carlo method to establish the 24 h power consumption of the three types of electric vehicles.Based on this,combined with the electric vehicle to the grid technology(V2G)and the difference in energy demand of different types of electric vehicles,predict the three types of electric vehicles 24 h FM capacity for high-frequency events and low-frequency events.A single physical model is established based on the working principle of the electric water heater.Statistic and analyze data such as the proportion of electric water heater models,daily use frequency,and different water consumption events in a community with 1000 households.On this basis,using Monte Carlo method to simulate and analyze the change of the total power of 1000 electric water heaters in the community in 24 hours.For different water consumption events,analyze and calculate the 24-hour frequency modulation capacity of the thousands of electric water heaters for high-frequency events and low-frequency events by changing the expected water temperature value input by the user of the electric water heater.Finally,on the basis of the above,an island microgrid model supporting the community with 1000 households is established.The power side is composed of photovoltaic power generation,wind power generation and diesel generator,and the user side load is composed of electric vehicles,electric water heaters and other basic loads.In order to improve the frequency modulation response ability of the island microgrid,the frequency modulation control strategies are studied from the power side and the demand side respectively.In order to reduce the frequency fluctuation and make the frequency control more accurate,the droop control of photovoltaic power generation is improved based on the characteristics of microgrid lines,and the simulation is carried out.Considering the influence of wind speed on DFIG participating in frequency modulation,improve and adjust the frequency modulation method of wind power virtual inertia control according to different wind speeds,simulate,verify and analyze the influence of different control parameter values on DFIG frequency modulation performance.In order to take into account the travel needs of different electric vehicle users,the particle swarm method(PSO)with user satisfaction as the objective function is proposed to solve the control strategy of the frequency modulation sequence of each electric vehicle participating in the system.Use decentralized control that considers the participation of electric water heater users in frequency modulation events to perform frequency modulation control for each electric water heater.The above-mentioned power supply side,demand side,and power supply side and demand side coordinated frequency modulation control strategy are simulated and analyzed by simulation software,and analyze the advantages and disadvantages of each module’s frequency modulation strategy. |
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