Research On Control Strategy Of Bidirectional DC/DC Converter In DC Microgrid

DC microgrid is the main direction of future research on new energy power generation.It has important significance in improving the utilization rate of renewable energy,alleviating the contradiction between energy demand and environmental protection,and improving the safety and reliability of power supply.Dual DC/DC converters can realize bidirectional transmission of energy and are an important part of building DC microgrid.This paper first introduces the research status of bidirectional DC/DC converters in circuit topology and control mode,compares the advantages and disadvantages of common topologies,and combines the requirements of background and project cost to select bidirectional half-bridge DC/DC converters.As the main topology of the study.The switching states of two different half-bridge DC/DC converters in different working modes are analyzed.The main parameters of the topology are calculated according to the design specifications and the device selection is carried out.At the same time,some problems of the topology in the DC microgrid are put forward.Then design the PI controller in the battery constant power charge and discharge mode and verify the experiment.The constant power charging of the battery together with the bidirectional DC/DC converter can be equivalent to a constant power load and exhibits a negative damping characteristic.The cascading of the constant power load and the distributed power converter easily leads to system oscillation,which brings safety hazards to the stable operation of the DC microgrid.By establishing the small-signal model of the converter at the equilibrium point,the transfer function of the converter duty cycle and the bus voltage is derived.Theoretically,the reason why the source-side converter adopts the traditional PI control cannot improve the stability of the system.The PSIM simulation model is established.From the simulation results,the stability of the battery running through the bidirectional DC/DC converter using traditional PI control and hysteresis control in the DC microgrid is compared.The mode switching strategy of the bidirectional DC/DC converter in the DC microgrid is deeply studied.Finally,a new control strategy based on slope calculation for predicting peak current control is proposed.A digital control system based on TMS320F28335 is designed.A 3KW bidirectional DC/DC converter experimental prototype is developed as a core.The effectiveness of the new control strategy.