Research On Converter Based On Multi-source Cooperative Control In Dc Microgrid System

Compared with the traditional AC microgrid,the stability of the DC microgrid is only determined by the DC bus voltage.The essence of the DC bus voltage fluctuation is the fluctuation of the bus capacitor power,so how to coordinately control the balance of distributed power,energy storage devices,and grids and other multi-source power and load power is the key to studying DC microgrids.The research object of this paper is a multi-source cooperative DC microgrid system with photovoltaic as a renewable distributed power source and storage battery as an energy storage device.In this paper,the converter control strategy and the overall coordinated control strategy in the system are analyzed and studied respectively under the on-grid and off-grid states.The main content includes the following parts:First,introduced the concept and structure of the microgrid and analyzed the structure of the multi-source cooperative DC microgrid system and the topology and control strategy of each interface converter.Then the mathematical models of photovoltaic cells and battery are constructed and their output characteristics are analyzed.Secondly,the structure and control strategy of the converter in a multi-source cooperative DC microgrid are studied.The photovoltaic power generation device adopts MPPT control and CVC according to different operating states of the system.The implementation of MPPT is based on an improved adaptive disturbance observation method.CVC uses a voltage and current double closed-loop control strategy.At the same time,the topology of the converter connected to the microgrid is a bidirectional half-bridge DC/DC circuit.The structure and principle of the topology are analyzed in detail,and an improved automatic charge and discharge control strategy for the energy storage system is proposed.Then,when the system is connected to the grid,the model and control strategy of the three-phase full-bridge PWM converter with grid-side interface are studied.A current feedforward control method is proposed to solve the problem that the traditional PI double closed-loop control cannot smooth the fluctuation when the bus voltage is disturbed.In addition,this paper proposes a new three-phase sliding DFT phase-locked method.This phase-locked loop can accurately extract the fundamental positive sequence component of the grid voltage under various distortions of the grid voltage.Fourth,the working mode of each micro-source interface converter is controlled according to the DBS control strategy.The system is divided into two operation modes: on-grid and off-grid modes.In off-grid mode,the photovoltaic unit operation control and the energy storage unit operation control are studied separately.Finally,the overall simulation model of the multi-source cooperative DC microgrid system was built in the MATLAB/Simulink simulation platform,and the control strategies of each converter and the cooperative operation of the entire system were simulated and verified.On this basis,the system hardware experimental platform whose main control chip is DSP28335 is designed and the corresponding software control program is written.Finally,the effectiveness of the control strategy proposed in this paper is verified by experiments.