Research On Modeling And Control Of Power System For Power Battery Second Use In Communication Field

The development of electric vehicles is an important way to improve the competitiveness of the automobile industry,ensure energy security and develop a lowcarbon economy,and has become one of the medium-and long-term strategic plans for energy industries in various countries.However,the rapid development of electric vehicles has led to a sharp increase in the number of power batteries used.When the capacity of the power battery declines by 20%-30%,it will be retired from the car.The retired power battery needs to be tested,sorted and reorganized before second use.At present,the second use of retired power batteries is mainly concentrated in the fields of wind power,photovoltaic power generation,and energy storage,but less used in the field of communication systems.The power supply system used for the second use of power batteries in the communication field faces the following problems: 1)Retired power battery packs of the same type in parallel may cause excessive parallel current to burn out the battery contactor;2)The Four Switches Buck-Boost(FSBB)converter is connected in parallel to the bus,and a control method is needed to make the converter operate efficiently;3)The cascade of front and rear converters in the power supply system is easy to cause system instability due to input and output impedance mismatch.In response to the above problems,the research contents carried out in this thesis are as follows:The thesis studies the problem of excessive current in the same type of power battery packs when used in parallel is studied.A suppression method based on series negative temperature coefficient(Negative Temperature Coefficient,NTC)resistance is used.The battery voltage data is obtained through the HPPC experiment,and the internal parameters of the battery cell are identified by the data fitting method,thereby establishing the battery cell model,and comparing the model simulation data and the experimental measured data to verify the correctness of the battery cell model.The method of connecting NTC resistors in series between two battery packs is used to solve the problem of excessive current at the instant of parallel connection of battery packs.The NTC resistance model was established,and the battery parallel simulation was carried out in combination with the battery pack model.The maximum parallel current was analyzed using the simulation results,thereby determine the NTC resistance value,and the effectiveness of the method was verified through experiments.The thesis studies the modulation mode of the FSBB converter in buck-boost working mode,and proposes a mixed-mode control strategy based on the minimum RMS value of the inductor current.The working principle of different modulation strategies and the implementation method of soft switching under the buck-boost working mode of FSBB converter are analyzed,and the RMS value of the inductor current and output current in four modulation motheds of four modes are deduced.The generalized Lagrange function method is used to optimize the inductor currents of different modulation modes under four modes to obtain the optimal modulation mode with the smallest RMS value of the inductor current when the output currents are the same.The influence of the inductance value on the maximum output current under the optimal modulation mode is studied,and the design method of the inductance parameters is determined.According to the optimization results,a mixed-mode control strategy is obtained,which realizes the soft switching of the four switches in the full load range and minimizes the RMS value of the inductor current.The thesis studies the stability problem caused by impedance mismatch in cascaded converters in power supply systems,and proposes a stability control method based on parallel virtual resistors.The large-signal model is established by the state-space averaging method to analyze the open-loop stability of the cascade system,and the parameter range of the parallel resistance that can be stable within the full load range is determined based on this;The effect of parallel virtual resistance on the closed-loop output impedance of the source converter in cascade system is analyzed,and the active control implementation method of parallel virtual resistance is studied.The Lyapunov indirect method is used to obtain the stability criterion of the control strategy,and then the parallel virtual resistance parameters that can satisfy the stability of the entire system are selected.Finally,simulations and experiments are used to verify the effectiveness of the parallel virtual resistance method.