Study For Master-slave Control Input-series And Output-parallel Full-bridge DC-DC Converter System

At present,scientists at home and abroad pay more and more attention on the research on direct current(DC)grid.However DC grid is facing with the challenge by DC-DC converters whose voltage power are both high.The DC-DC converter topology containing many modules connected in series or parallel is more capable to meet the needs of different voltage levels and power levels,with a good prospect.In order to overcome the problem of "high input voltage and high output current" in DC grid,this paper studies Input-Series and Output-Parallel(ISOP)DC-DC converter system whose basic module is the full bridge converter with an isolated transformer.The main problem of ISOP converter system in the application is how to realize the balance between input voltages and between output currents of every module.In this paper,the importance of input voltage balancing and output current balancing of ISOP system in DC power grid is analyzed in detail,and the relationship between them is derived.As long as input voltage of each module is balanced,output current can be balanced.In view of this characteristic,the master-slave control strategy with phase shift control is proposed.The main module controls the output voltage,and input voltages and output currents are balanced by the slave module.Either the main control circuit or slave control circuit includes two parts: the first part of the main control circuit is output voltage error amplification,adopting the output voltage feedback control method,and the second part is the phase shift control circuit;the first part of the slave module controls the input voltage difference to zero to balance input voltages of two adjacent modules,and the second part is the phase shift control circuit,too.In this paper,the mathematical model of the first part of the slave control circuit is established,and the transfer function block diagram of the input voltage difference sampling signal circuit is derived in detail.Then,the operation principle of the phase shift controlling full bridge DC converter is analyzed in detail.The effect of output filter inductor current disturbance and input voltage disturbance on duty cycle(phase shift angle)is derived,and the equivalent small signal model of the master-slave control ISOP full bridge DC converter system is established.On the basis of theory analysis and the principle of phase-shifter UCC3895,this paper build two modules ISOP converter system,carrying out a series of simulation and the simulation results are analyzed.Finally,the principle prototype is built,and the feasibility of the master-slave control strategy is verified.