The Control Strategy Research For Series And Parallel System Based On Bidirectional DC/DC Converter

Multi-module series-input and parallel-output(SIPO)bidirectional DC/DC converter can be applied on the occasion of high-voltage or large-current is needed,such as power electronic transformers(PET).For reliable operation,special attention should be paid to ensure input and output sharing of voltage and current among modules.In this thesis,an improved isolated bidirectional DC/DC converter topology,which has no reactive current and reduces the cost,is presented for the dual active bridge(DAB)topology.For the actual application of switching problems,the dead time and the through time are setted up to ensure the normal operation of the circuit and RCD absorption circuit design after Buck/Boost working mode and modulation strategy are studied.Aiming at the problem of the input sharing of voltage,a droop voltage sharing control strategy is presented,which is based on the research of an improved bidirectional DC/DC topology and control.In the control strategy,module's input/output voltage and inductor current are acquired and the input voltage sharing control is realized by using the droop characteristic about inductor current compensation value and the input voltage.Simulation and experimental verification are carried out on Matlab/Simulink and RT-LAB hardware-in-the-loop simulation platform.Due to the droop voltage sharing control strategy makes the each module independent and parameters remain same,the transfer function is derived under the droop voltage sharing control strategy by small signal analysis in Buck/Boost and the stability and parameter selection analysis are carried out by zero pole distribution.The system is still able to maintain stability after adding the sharing of voltage and parameter selection needs to be as large as possible.For the influence of different parasitic resistance on the sharing of voltage,the zero-pole distribution of the equivalent resistance is used to analyze and the parasitic resistance has little effect on the steady-state sharing of voltage.As the total voltage of the input side changes,the input voltage of single module does not follow the total input voltage changes to achieve dynamic input sharing.In order to solve the problem of dynamic sharing of voltage in the system,the secondary regulation design,which adopts the method of translating droop curve to improve the control performance and realize the dynamic voltage sharing,is carried out.