| In recent years,with the continuous advancement of photovoltaic(PV)power generation and energy storage technology,the DC microgrid system based on PV power generation and energy storage has been widely concerned by industry and academia at home and abroad.Due to the intermittent and fluctuating characteristics of PV power generation,and the low-frequency fluctuation of the DC bus voltage when various loads are connected to the DC microgrid system,the energy storage system with a bidirectional DC-DC converter is indispensable link to solve the above problems.How to use energy storage system to improve the stability of DC microgrid has important theoretical significance and practical value.In this paper,the bidirectional DC-DC converter is taken as the research object and the control strategy of DC bus voltage fluctuation suppression is deeply studied.(1)The development status of PV power generation,energy storage technology and DC microgrid are introduced briefly.The mathematical model of the non-isolated half-bridge bidirectional DC-DC converter is studied.The PI control method of the bidirectional DC-DC converter for PV power generation and energy storage is discussed.The limitation of the PI control strategy based on linear feedback theory is analyzed in detail.(2)In order to improve the dynamic performance and anti-disturbance ability of the PV power generation and energy storage system,an active disturbance rejection control(ADRC)method for the bidirectional DC-DC converter is proposed in this paper.The principle of the ADRC is analyzed theoretically,the ADRC controler in different working modes are designed,and the performance of the ADRC controller is analyzed deeply.In addition,the immune algorithm is used as the parameter optimization mechanism to improve the dependence of the system performance on the controller parameters in this paper and is added to the control system of the bidirectional DC-DC converter based on the ADRC.An adaptive ADRC method for the bidirectional DC-DC converter using immune algorithm is proposed in this paper.Compared with the traditional ADRC strategy,adaptive adjustment of controller parameters can be achieved and the dynamic performance and robustness of the system can be further improved.(3)Two control strategies for the bidirectional DC-DC converter based on predictive current control are studied deeply,and the application of deadbeat predictive current control in the PV power generation and energy storage system is discussed.Firstly,aiming at the problems of irregular switching state and unfixed switching frequency existing in the traditional finite set model predictive control method,a predictive current control method for the bidirectional DC-DC converter based on optimal vector operating time is proposed in this paper.The control of the calibrated frequency of the system is realized by calculating the action time of each vector and using a new objective function.Compared with the traditional predictive current control strategy,the predictive current method based on optimal vector operating time can achieve better steady-state control effect.Secondly,in view of the suppression problem of the DC bus voltage fluctuation under the condition of multiple disturbance sources,a predictive current control method for the bidirectional DC-DC converter based on feedward control of a nonlinear disturbance observer is proposed in this paper.The second-order tracking differentiator is used as the disturbance observer to estimate the complex disturbance in the system.The influence of disturbance on the system is reduced by feedforward control.This method further improves the dynamic performance and anti-disturbance under multiple disturbance sources.(4)In order to improve the system efficiency,expand the converter capacity,reduce the current ripple,and improve the application of the half-bridge bidirectional DC-DC converter in high-power and high-current situations,three interleaved half-bridge bidirectional DC-DC converters toplogy is adopted as the interface circuit of the energy storage device.A current sharing control strategy for the interleaved bidirectional DC-DC converter based on the virtual impedance droop is proposed in this paper.This method reduces the current sampling link in the system,and has a good current sharing effect.(5)The simulation model and experimental platform are built.A large number of simulation and experimental results show that the above control strategies can effectively solve the DC bus voltage fluctuation problem under the various working conditions and the current sharing control problem of the interleaved parallel system. |
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