Research On Voltage Fast Recovery Control For Supercapacitor Interfacing Bidirectional DC/DC Converter

The intermittency of distributed energy and power fluctuation of load will directly affect the stability of DC microgrid,causing bus voltage fluctuation and affecting normal work of the related equipment in DC microgrid.Therefore,the stable control of bus voltage in DC microgrid become a core problem,which is particularly important when the DC bus is disturbed by power disturbance at different time scales.In order to solve the problem of instantaneous power imbalance of the DC bus,the idea of capacitor charge balance control(CBC)is introduced into the bidirectional DC/DC interfacing converter of energy storage system in DC microgrid to achieve fast recovery of bus voltage.The main work is following three aspects:Firstly,the bidirectional CBC control strategy is adopted.The dual-port stable control of interfacing converter is realized by combining the average current mode control and hysteresis current limiter in steady state,while fast recovery of bus voltage is achieved through the bidirectional CBC control in large-signal transient.After completing the matching of supercapacitor monomers,a small signal model of bidirectional DC/DC interfacing converter under the output control of complementary PWM is established.On this basis,the average current mode controller is compensated in continuous domain and discretized in discrete domain,and the hysteresis current limiter is added to achieve overvoltage and undervoltage protection for supercapacitor.Secondly,the filter capacitor on bus side is selected as characteristic control object.Based on two steady-state recovery conditions,a bidirectional CBC control law is derived,and the research idea of universal digital CBC control for indirect prediction of capacitor current variation is summarized.At the same time,the implementation,timing construction of CBC control and control flow of hybrid control strategy are given.Based on the existing CBC principle for controlling the unidirectional current,the bidirectional CBC control expands and optimizes the idea of indirectly predicting the change of capacitor current,and obtains the general substitution method of node current and the corresponding control law,so as to achieve the purpose of fast controlling bidirectional current in transient state and fast recovery of bus voltage under power fluctuation in DC microgrid.Finally,according to the control scheme studied,the hardware and software design of supercapacitor energy storage system in DC microgrid is completed,and the corresponding simulation model and hardware experimental platform are built.The simulation and experiment of bus voltage recovery and overvoltage/undervoltage protection for supercapacitor are carried out.The results show that the bidirectional CBC hybrid control strategy can achieve fast recovery of bus voltage,and the controller has a good protection function of overvoltage and undervoltage.