| EAST(Experimental Advanced Superconducting Tokamak)is the first all superconducting Tokamak device designed and developed by China,and also the first all superconducting Tokamak nuclear fusion experimental device in the world.EAST fast control power supply is an important part of the active feedback control system of plasma vertical displacement,which is used to suppress plasma vertical unstable displacement.At present,EAST fast control power supply adopts H-bridge cascade/parallel topology.There are 18 groups of single-phase full-bridge inverters.The whole inverter system adopts complex carrier phase shifted modulation.Every three H-bridges are cascaded into one branch,and there are six branches in total.The maximum output current is ±9 k A and the maximum output voltage is ±1.6 k V.Therefore,EAST fast control power supply system is bulky with complex topology and control strategy.In this thesis,from the point of view of optimizing EAST fast control power supply topology,reducing power supply volume and simplifying control strategy,an active lossless snubber circuit of H-bridge is discussed in order to solve the problem of voltage overshot at turn-off transient.Firstly,this thesis analyzes the operation mode of a single switch module in H-bridge.Based on the operation logic of the main switch and auxiliary switch in the snubber,the working state of each component in a single switch module is analyzed under the two circuit states of overdamping and underdamping,and the overshoot phenomenon is calculated theoretically.Then the influence of circuit components on the turn-off overshoot of switch in the snubber and the basis for component parameter selection are analyzed.Simulink simulation results verify the theoretical calculation and the above analysis process.Compared with the current H-bridge RC snubber of EAST fast control power supply and RCD structure,the active lossless snubber circuit has some advantages in ohmic loss,switching frequency and turn-on transient characteristics of main switch.Secondly,based on two different modes: without phase shift and with phase shift,the operation state of the whole H-bridge inverter and the commutation circuit of H-bridge in each stage are analyzed and compared.According to the Simulink simulation operation waveforms of the main switch,auxiliary switch and corresponding snubber capacitor in the two modes,the turn-off overshoot,ZVS(Zero Voltage Switch)/ ZCS(Zero Current Switch)and other phenomena in the operation process are analyzed,and the commutation analysis results are verified.The results show that the active lossless snubber circuit has less ohmic loss than the RC structure.The introduction of auxiliary switch instead of R does not increase additional ohmic loss theoretically.In practice,the auxiliary switch has only a small amount of conduction loss.Finally,a confirmatory experiment with 5k@30V@3A is carried out.The preparation of the experiment includes circuit design,driving signal generation based on DSP(Digital Signal Process)e PWM module,selection of some main components and related calculation.By analyzing the operation characteristics of main switch,auxiliary switch and snubber capacitor in different modes and different circuit positions,the above analysis and simulation results are verified.It mainly includes verifying the ZVS/ZCS phenomenon of the switches on the H-bridge under the two operating modes,the difference in the number of charge and discharge stages of the snubber capacitors on the leading leg and the lagging leg under the phase shift control mode,and explaining that the introduction of the auxiliary switch instead of R does not lead to excessive losses for the entire H-bridge to avoid problems such as increased volume and difficulty in heat dissipation of the power supply.The switching frequency of the power supply can also be further improved.Through the analysis and research in this thesis,the active lossless snubber structure is not only simple in structure,easy to select parameters and simple in control logic,but also avoids the ohmic loss caused by traditional RC and RCD structure in high-power circuit and the space and heat dissipation problems caused by high-power resistance.Therefore,the volume of the power supply can be further reduced and the switching frequency can be further improved.Compared with RC and RCD,the H-bridge snubber structure does not participate in the operation of the main circuit when the main switch is turned on,which avoids the problem of excessive current peak when the main switch is turned on and has higher reliability.The H-bridge scheme in this thesis can provide some reference for the structure design of fast control power supply in the future.Figure [47] table [4] reference [54]... |
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