Research And Equipment Development Of Input-series Output-parallel High Voltage DC/DC Converter

With the depletion of traditional fossil fuels as well as the rapid rise of renewable energy,the energy structure reform is imperative.AC power grid is more and more powerless in the term of large-scale renewable energy access,DC power grid has become a hotspot of many solutions to this problem.One of the key technologies in the development of DC power is the high-voltage DC/DC conversion technology.DC/DC converter that uses multiple modules combined in series-parallel can be applied to high input-voltage high-power occasions.The input-series-output-parallel(ISOP)combination DC/DC converter is the outstanding choice for high input voltage and low output voltage applications.Achieving input voltage sharing(IVS)and output current sharing(OCS)is critical for the normal operation of the ISOP combined converter.Focus of this paper is mainly reflected in the following aspects:(1)Taking full bridge(FB)DC/DC converter as the basic module,the structure of the ISOP DC/DC converter is studied.The working principles of the full-bridge DC/DC converter are described and the influence of the transformer leakage inductance on the full-bridge DC/DC converter is analyzed,and then the small-signal model of full bridge DC/DC converter is established.On the basis above,the FB-ISOP overall small-signal model is built,and the frequency domain analysis of the system is carried out by using perturbation analysis method,then the transfer function relation between each disturbance variable is deduced.(2)Regarding input voltage sharing and output current sharing as the main target,control strategy for ISOP is studied and designed.Taking the input negative impedance characteristic of the switching DC/DC converter as the entry point,the mechanism and instability based on the traditional dual-loop OSC control are revealed.On this basis,a three-loop control strategy is studied,and for the control strategy,a detailed parameter design and stability analysis are carried out.The simulation results show that the control strategy and the designed parameters can realize the stable output of the system as well as OCS and IVS.(3)Taking a 10kV/100kW ISOP converter design as an example,the principles and steps of main circuit parameters selection are described in details,and according to the parameter design principles above,a three-module ISOP experiment platform is built,then the control system for the platform is designed.The experimental results show the validity and correctness of the research.