Research On Modulation And Control Strategy Of Dual Active Full-bridge Converter Based On Predictive PI

Dual Active Bridge(DAB)converters are widely used in various new energy systems and distributed microgrid structures in recent years for interconnection and grid integration between subsystems due to their electrical isolation,wide voltage output range and real-time switching of power transfer direction.The voltage DAB converter,specifically a sample of a DAB converter in the development phase in the on-board power supply research laboratory of a company,has been chosen as the subject of this paper.The research work is carried out in terms of modulation method solution,system model identification and communication delay response,steady state magnetic balance control and closed loop control system design,with the aim of improving the efficiency and control quality of the DAB converter.The main work and innovation points of this paper are as follows:Firstly,the traditional SPS voltage closed-loop control method is analyzed and verified by experiments,and two further research directions of modulation strategy optimization and control system design are pointed out.In terms of modulation strategy,the introduction of new control quantity is the basis for improving the working efficiency of DAB.In this paper,TPS modulation with two additional free variables is introduced to study the working principle of DAB converter under this modulation method.The inductive current decomposition method is used to simplify the principal analysis process,and the feasible working mode and corresponding power transmission characteristics in TPS modulation are obtained.A new TPS loss optimization modulation strategy is proposed,which can consider the soft switching condition and reduce the total loss of the converter while ensuring the minimum on-off loss.In terms of control system design,modeling and controller design are studied for DAB converters with sampling and communication delay at high switching frequencies found in practical engineering.The hysteresis bias relay feedback method is selected to identify the system model,and the transfer function model containing the time delay information is obtained.After that,the Predictive PI algorithm is used to design the closed-loop controller,and the control effect of the algorithm and the traditional PID control in dealing with the system with time lag is compared and analyzed,and the control quality of the DAB converter control system with time lag is successfully improved.Then,in view of the magnetic balance problem of DAB converter existing in engineering practice,the generation principle and elimination conditions of steady-state DC bias under TPS modulation are analyzed,the transfer function of switching signal duty ratio and DC bias under TPS modulation is obtained,and the control structure of eliminating DC bias is proposed.Finally,to further improve the response speed of DAB converter and the stability of load switching,a virtual load power control structure is designed based on loss power compensation based on the idea of direct power control.The virtual load power is taken as the transmission power set point of the converter to make its real output power conform to the expected load power.The simulation results show that the structure can achieve the desired goal and has certain superiority.