| The industrial microwave system has the advantages of uniform heating,precise process control,high heat transfer efficiency,and strong penetration ability.The product quality and production efficiency of the process are greatly improved.Moreover,the economic benefits are remarkable.As a new type of industrial processing technology and equipment,its development and innovation for food,pharmaceutical,chemical,construction,ceramic,and other industries are significant.Magnetrons are used to generate high-power industrial microwaves.High-voltage electric field power is loaded to the magnetron anode to form an accelerating electric field.A low-voltage filament power supply heats the cathode to produce free electrons flying to the anode.Moreover,by the action of the high-frequency magnetic field,the magnetron cavity has high-frequency oscillation and thus emits microwaves.However,the existing microwave power supply uses an industrial frequency transformer combined with low-frequency electrical energy conversion to obtain a high-voltage electric field power supply and low-voltage filament power supply.It leads to output voltage fluctuations and weak voltage regulation.However,the conventional industrial frequency conversion has power density,low conversion efficiency,and other problems.Therefore,it restricts the development of microwave equipment.Resonant high-frequency DC converter has the advantages of high operating efficiency,high power density,and stable output.It has application advantages in microwave systems.This paper is supported by the Guangdong Province Pearl River Talents Program "Guangdong Introducing Innovative and Enterpreneurial Teams",the enterprise transversal project "Development of High Power Microwave Power Supply," and the Hunan Province Major Project "Key Technology and Demonstration of Large Scale Energy Storage System to Support Safe and Efficient Operation of Power Grid." It conducts an in-depth study on microwave power supply topology,control mode,and high-frequency transformer optimization.The main research contents are as follows:(1)The hybrid microwave power supply topology of LLC and DAB converter is proposed for the high-efficiency operation of high voltage output of microwave field power supply.It consists of multiple fixed frequencies and fixed duty cycle LLC resonant converter unit outputs connected in series to achieve most of the power output.A single Dual Active Bridge(DAB)converter regulates the output voltage.output.A single Dual Active Bridge(DAB)converter regulates the output voltage.Further,the high voltage wide range output is achieved by the throwing and cutting LLC converter units and continuous regulation of the DAB converter.However,the high isolation transformer of the electric field power supply has significant parasitic parameters such as primary and secondary parasitic capacitance and leakage inductance.Therefore,it leads to the difficulty of existing models to accurately describe the operation mode of the converter.For this purpose,an equivalent converter model with parasitic parameters is developed.The operating modes of the converter are analyzed.The time-domain equations of each mode are derived.Meanwhile,a fast solution method for the time domain equations is given based on each mode boundary and power conservation condition.The gain,voltage ripple,and soft switching realization conditions are derived.Finally,the proposed microwave electric field power supply and the model’s accuracy in containing multiple parasitic parameters are verified.(2)The switching control method based on the sliding-mode variable structure is proposed to demand high-efficiency wide voltage range regulation of microwave field power supply.It achieves wide-range output voltage regulation.The method utilizes the characteristics of the DAB converter energy bi-directional conversion to attain fast and continuous regulation of the output voltage.It also extends the output voltage regulation range by combining it with the LLC converter dropout.The sliding mode controller realizes the fast response of the voltage switching process during the switching process.The switching operation of the LLC converter is analyzed.The switching rule of output voltage smoothing output is derived.Moreover,the optimized design of control parameters is carried out.Based on this,the output characteristics and losses of the proposed converter are analyzed.The proposed converter’s voltage regulation range,gain and ripple characteristics,and efficiency are compared with typical converters.Finally,the simulations and experiments verify the proposed control method and parameter design.(3)The microwave electric field power supply is sensitive to the parasitic parameters of the high-frequency transformer.Also,an EE-type multi-winding transformer structure is proposed considering the demand for high isolation and high power density of high-frequency transformers.Multi-objective optimization is also carried out.In this structure,the original secondary winding is around the middle column of the EE-type core,so the magnetic field is evenly distributed,and the leakage is small.The secondary side is wound in parallel and output separately,which realizes the self-leveling of multiple rectifier bridges in series.The core center column and primary side windings are built with heat dissipation air ducts to reduce the heat build-up in the center column.A multi-physics field model of the increased frequency high isolation transformer is developed.Meanwhile,its electromagnetic and temperature distribution characteristics are analyzed.Further,the expressions for the set parameters of its leakage inductance,parasitic capacitance,and temperature are derived.On this basis,the operating frequency,primary and secondary spacing,and primary turns of the transformer are optimized with multiple objectives,taking into account the parasitic parameter constraints and the operational characteristics of the resonant converter.Finally,a prototype transformer with 2.5 k V output 60 k V isolated 15 k W is developed.The optimization enables the LLC converter to achieve up to 98.6% operating efficiency over a wide load range.(4)The filament power supply topology of resonant push-pull converter combined with synchronous Buck cascade and its control method is proposed for high isolation,efficiency,and high power density of magnetron filament power supply.The front-stage resonant push-pull converter operates in an open-loop.The rear stage synchronous Buck introduces feedforward control to stabilize the output.High voltage isolation is achieved,and trans-high voltage feedback control is avoided.The proposed topology presents series resonance on the output side of the push-pull converter.It improves the operating efficiency and compensates for the leakage drop.At the same time,the Buck converter input is affected by the open-loop output voltage disturbance of the front stage.Therefore,this paper introduces feedforward based on synchronous Buck output control the backstage.It suppresses the perturbation of the supply voltage by the input voltage fluctuation.Based on the proposed topology,a transformer design method with a toroidal core and separated sector winding is proposed considering the need for high isolation of filament power supply.The complete design flow of the highly isolated filament power supply is also given.Based on the above cascade structure,a prototype filament power supply with 11-13 V output and 60 k V isolation was developed,achieving 92.8%.(5)Based on this paper’s proposed hybrid power supply structure,the engineering design of a microwave electric field power supply with 120 k W/20 k V output is given.The hardware offers the design of crucial parts such as switching devices,driving circuits,sampling circuits,auxiliary power supply,and converter insulation.The software part gives the main program’s design flow and interrupts the program.In addition,the feasibility of the hybrid microwave electric field power supply design is experimentally verified.This hybrid structure’s hardware and software design also provide an essential reference for applying other high-voltage high-power DC power supplies. |
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