Research On High Power And Wide Range LLC Resonant Converter

The LLC resonant converter has the advantages of high efficiency,high power density,etc.,and is widely used in applications such as telecommunication power supply,new energy power generation and electric vehicles.Many scenarios require it to have a wide gain range adjustment capability.Improving the efficiency of LLC converters within the whole range,especially in highpower systems,can improve equipment performance,reduce power loss,and bring significant economic benefits.This research takes the high power wide-range LLC resonant converter as the research object.Aiming at key characteristics as wide gain range expandability,high voltage/high current adaptability,this research deeply analyzes its topology and control methods,and explores how to maintain high efficiency while expanding gain range.First,this research proposes a high-gain frequency conversion,phase-shift asymmetric and DPWM combined flexible variable-mode control strategy for the full-bridge LLC converter,which greatly broadens the voltage gain range of the converter and achieves high efficiency in the wide range at the same time.The primary side switches are zero-voltage switching on in the full range and the secondary side switches are zero-current switching off in a larger range.The proposed control method has a non-switching control logic,and there is no transient overshoot during a wide range of work.This research explains in detail the state machine matching and transition methods of the sub-modes involved in the control.Based on the established design platform combining theoretical analysis and digital calculation,the parameter design of the proposed wide-range LLC scheme is given in detail,and engineering implementation details as well.Finally,the proposed flexible wide-range control strategy is verified by experiments.The gain and efficiency results of the prototype prove the feasibility and effectiveness of the scheme.Secondly,for the application scenarios of high power,high voltage and wide gain range,this research proposes a clamp-bridge combined multilevel LLC converter and comprehensively analyzes its high-efficiency wide-range control method.This research analyzes in detail the various sub-operating modes of the proposed LLC converter,proposes the FB-LLC equivalent control mode and the multilevel control mode,and unifies the flexible variable mode design of the multilevel converter.The wide-range variable mode control method proposed makes full use of the characteristics of the multilevel converter with more switching states and rich working modes,and considers voltage balance,soft switching,etc.While expanding the gain range,it guarantees the high working efficiency of the full control range,improving the performance of the multilevel converter.Experimental results show that the proposed multi-mode controlled multilevel LLC converter can not only achieve a very wide voltage gain adjustment range,but also has a high operating efficiency in the entire operating range.It is suitable for high voltage wide gain applications and can efficiently replace the two-stage DC/DC wide-range converter in the corresponding system.Then,this research takes a high-power multi-channel series bridge three-level LLC converter as the object,and conducts multi-mode multi-channel optimization research.Based on a comprehensive summary of LLC converter power expansion methods and the application characteristics of each expansion method,and an in-depth analysis of the characteristics of multichannel interleaved parallel system,this research proposes a multi-mode-based control type interleaved parallel method,and explains its benefits and costs.In addition,this research proposes an upper-level optimization controller to schedule the operation mode of the system under different load conditions for system,combined with the single-channel multi-mode optimization,which greatly improves the system efficiency under wide power and gain range.Finally,this research realized a prototype of a series bridge three-level LLC converter with a rated input of750 V,a rated output of 100V/200A/20 k W,and 4 channels in parallel.Control logic such as interleaved parallel and adaptive multi-channel load optimization are tested.Experimental results show that these proposed control methods can reduce current ripple and improve system efficiency.Finally,this research compares the operating characteristics,advantages and disadvantages of a phase-shifted full-bridge converter and a wide-range LLC converter in a wide range application.And it takes a wide input two-stage power system with a bidirectional switch PFC+FB-LLC structure as a research example,establishing an optimization model,and shows that by introducing multi-mode control in the LLC part,the efficiency of the two-stage system at wide gain points can be improved.The experimental result shows that the efficiency of the twostage system designed for gain optimization is significantly improved when working at a wide gain point,which verifies the effectiveness of the proposed optimization method.Based on gain and loss analysis,this research adopts the idea of multi-mode and flexible variable mode to control and upgrades the traditional LLC converter,so that the LLC converter can work with high efficiency in the whole wide gain range.It has certain reference significance for the high-efficiency design and optimization of other wide-range DC/DC and DC/AC converters.