| Microgrid has received extensive attention and research of scholars both at domestic and abroad gradually,which is an effective organization form of integrating distributed generation,energy storage system and load.Previous studies always focused on AC microgrid,but the research significance of DC microgrid has become increasingly prominent with the increase of distributed generation with DC characteristics and DC load.The research on DC microgrid was mainly focused on the internal microgrid,such as coordinated control strategies and energy storage optimization configuration within DC microgrid,but there is not much research on energy dispatching control strategy for DC microgrids.The control strategy of interconnection and energy dispatching of flexible interconnection switch with DC microgrids is analyzed in this thesis.The research of the DC power distribution system consisting of the flexible interconnection switch and DC microgrids was studied in the following aspects.(1)The working principle of the flexible interconnection switch in different working modes is analyzed in detail.The dual-carrier three-mode modulation method is used to realize flexible interconnection switch's smooth switching in the three modes of buck,buck-boost and boost.The single current loop and the voltage and current double closed loop control mode of the flexible interconnection switch are analyzed,and the correctness of the relevant theoretical analysis is verified by simulations and experiments.(2)A droop control strategy of flexible interconnection switch is designed to realize the flexible interconnection switch's function of interconnecting and dispatching energy between DC microgrids.The bus voltages of the microgrids on both sides is detected by the flexible interconnection switch and input into the controller,then the value and direction of the power flow according to the droop curve will be calculated by the controller.The setting of the droop curve is coordinated with the control of the internal energy storage converters of the DC microgrids,and the DC microgrids are supported by each other with the energy dispatching between them,then the bus voltages of both DC microgrids will be kept within a reasonable range.The parallel operation control strategy of flexible interconnection switch is also introduced,and the feasibility of flexible interconnection switch in parallel operation is proved.(3)To help the optimization and adjustment of energy storage unit's SOC(State of Charge)in the microgrids on both sides,the secondary adjustment function is added to the flexible interconnection switch on the basis of the droop control.Secondary adjustment means that the droop control curve of the flexible interconnection switch will translate based on energy storage unit's SOC on both sides.In order to maintain SOC within a reasonable range,after the flexible interconnection switch gets the energy storages' SOC of both microgrids,the amount of translation will be calculated.Energy will be dispatched from the high side to the low side,so the SOC is optimized and regulated,and the life of the energy storage units is extended.(4)The small signal models of the flexible interconnection switch is established in the three working modes,and the flexible interconnection switch in Buck mode is taken as an example,the mathematical model of flexible interconnection switch and DC microgrids is deduced.The stability of the flexible interconnection switch with droop control strategy is analyzed,and the influence of the change of the control variables on the stability of the DC microgrids is described.(5)On the aboved theoretical research basis,the effectiveness and correctness of the theoretical analysis and control strategy are verified by simulation model in Matlab/Simulink and hardware-in-the-loop simulation platform based on dSPACE1103. |
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