| In order to alleviate the energy shortage and a series of problems caused by the traditional power generation mode,DC micro-grid system based on distributed new energy generation has been developed and received extensive attention.Distributed generation improves energy conversion efficiency and reduces economic costs,but the power fluctuation will lead to the fluctuation of DC bus voltage,so the energy storage system will be connected to dc micro-grid to solve this problem.DC micro-grid is composed of new energy generation module,energy storage system module and load module.This paper studies the topology of new energy generation module,energy storage system module and its control strategy respectively.The low-voltage parallel high-voltage series(LPHS)DC/DC converter circuit can be used as a converter in a new energy power generation module and energy storage device system to connect a low-voltage source to a high-voltage DC bus.The working state of the converter is analyzed,and a small-signal model is obtained to design a double closed-loop control system.The steady-state relationship is calculated and analyzed in detail,and the voltage gain,current ripple,and voltage stress are explained through specific formulas and graphs.Interleaved modulation is used to reduce current ripple.Finally,simulations and experiments verify the feasibility of this converter and the effectiveness of its control strategy.The cascade structure is a common connection method in energy storage systems,which improves and stabilizes the voltage of the DC bus,and improves the stability and reliability of the system.Aiming at the modular cascaded bi-directional DC converter,analyze its working state,obtain a small signal model,and design a control strategy for the current loop and the independent voltage loop,so that the voltages between the modules are balanced and the DC bus voltage is stabilized.The interleaved modulation strategy is adopted to reduce the output voltage ripple and output current ripple.The effectiveness of the proposed control method is verified by simulation.Hybrid Energy Storage System(HESS)applied to the DC micro-grid can play the role of solving instantaneous high power,taking advantage of different energy storage components,and extending service life.The Hybrid Energy Storage System can keep the power supply of the System uninterrupted when the power generated by the new Energy generation System is insufficient.The use of a coupled inductor high-gain converter enables the low-voltage source to be connected to the high-voltage bus,which has the advantages of fewer power switches,lower losses,and lower costs.Hybrid energy storage adopts double closed-loop control strategy and uses a first-order filter to divide the current reference value by frequency.Currents with different frequencies are allocated to different energy storage elements for processing.The control strategy of a DC micro-grid system composed of a constant-voltage controlled photovoltaic power generation system,a hybrid energy storage system,and a load module in an isolated state is designed to improve the dynamic characteristics of the DC bus voltage during load switching.Finally,it is verified through simulation and experiment. |
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