Study Of Grid-Connected Dual Buck Bidirectional DC-AC Converter And The Switching Control

In recent years,the development of the renewable energy,represented by distributed energy,has been vigorously promoted followed by the rise of the DC micro-grid technology,the vehicle to grid technology and various types of energy storage system in our country.The bidirectional DC-AC converters are available in these applications.Therefore,the study of a highly efficient and reliable bidirectional DC-AC converter and the ensurence of the smooth and seamless switching control of its bidirectional operating modes is the primary work to achieve the effective use of distributed energy.Several traditional bidirectional DC-AC converters have been reviewed.And it is pointed out that there are bridge structures in these circuits,which have the disadvantages of the bridge-through problem and the dead-time which is not conducive to the high frequency design.It is contrary to the development directions of high frequency,high efficiency and high reliability.The current research states of various types of dual buck converter has been discussed.And it is pointed out that this kind of circuit overcomes the inherent defects of bridge structures.In addition,the research status and development directions of dual buck converter circuit has been summarized.Subsequently,a full bridge dual buck topology with high DC voltage utilization and low voltage stress of the semiconductor switches has been selected and applied in the field of bidirectional transformation to achieve rectification and inverter in the same topology.In this paper,the control strategy of selected converter has been studied according to the control target of bidirectional operating stably and bidirectional switching smoothly.The small-signal model of both grid-tied inverter and rectifier PFC in the continuous conduction modes of inductor current are established in detail,and the current inner loop and the voltage outer loop controller are designed in detail.Among them,the voltage outer loop not only serves to stabilize the DC bus voltage,but also determines the operating directions of the converter by its output,which plays a key role in switching of the converter operating directions smoothly and seamlessly.However,the design and practical application of PI controller is relatively complicated.Therefore,under the premise of the adoption of traditional voltage loop to ensure the judgement of bidirectional operation mode,the finite control set model predictive control(FCS-MPC)has been designed to realize inner loop current control,and the discretization model of the selected dual buck topology has been established according to the fundamental of MPC.In addition,the judgment of the voltage loop output and the phase of the reference grid voltage has been added in the traditional MPC,which reduces the computational burden in the single control cycle of the controller,which is beneficial to the application of high frequency control.The simulation results show that the proposed MPC method can ensure the accuracy of steady state and the dynamic response speed compared with the traditional dual-loop PI control method,which can guarantee the switching of the bidirectional operating modes smoothly and seamlessly.In addition,the modulator and the process of parameters tuning are unnecessary and the control method is simple.Finally,the software and hardware of the prototype have been designed and the TMS320F28377D has been utilized to build the experiment prototype.The feasibility of theoretical analysis of this converter and the bidirectional operating and switching control methods have been verified by the experimental results.