Research On Phase Separation Rectification Control Strategy Of Thermoacoustic Power Generation System

Thermoacoustic power generation system utilizes the thermoacoustic engine to drag the permanent magnet linear generator to perform high-frequency reciprocating linear motion,thereby realizing the conversion of thermal energy to electric energy.The thermoacoustic power generation technology can realize the collection and utilization of low-quality heat sources such as solar energy,industrial waste heat and nuclear reactor waste heat.Under the energy crisis and the increasingly serious environmental pollution,the thermoacoustic power generation technology has more room for development.However,due to the special operation conditions of the linear generator,the output voltage is a three-phase non-sinusoidal asymmetric waveform with high harmonic content,resulting in low utilization ratio of electric energy.Therefore,by selecting an appropriate rectification control strategy,it is of great significance to reduce the harmonic content of input current and improve the utilization ration of the electrical energy output by the thermoacoustic generator.In this thesis,the characteristics of electric energy output by permanent magnet linear generators in thermoacoustic power generation system are studied in the following aspects:Firstly,on the basis of fully understanding the characteristics of the voltage output by the permanent magnet linear generator and the active power factor correction technology,a rectifier program of combined three-phase two-stage PFC is proposed.The topological structure and control strategy of the pre-stage and post-stage main circuit are analyzed and compared respectively,and the Boost PFC circuit structure based on the average current control is applied in the pre-stage circuit.The post-stage circuit adopts a phase-shifted full-bridge circuit structure with an isolation transformer,and analyzes the realization conditions of the zero-voltage switching state.Secondly,the design of the pre-stage and post-stage main circuits is analyzed respectively,and the design process of the related parameters of the components in the pre-stage and post-stage circuits is provided.The hardware circuit of the pre-stage and post-stage is built by Multisim simulation software to verify the rationality of the design of the parameters in the pre-stage and post-stage circuits.Then,the control circuit of the pre-stage and post-stage is designed.The UC3854 control chip is selected as the controller of the pre-stage circuit.The phase-shifted full-bridge circuit of the post-stage takes UC3895 control chip as the controller And the design of parameters in the both control circuits is provided separately.The specific parameters of the resonant network are analyzed to provide a theoretical reference for the zero-voltage switching of the switching tubes.Finally,based on the analysis of the working mode of the pre-stage Boost PFC circuit and the post-stage phase-shifted full-bridge circuit,the circuit simulation is performed by Matlab/Simulink simulation software,and the PFC circuit is analyzed and compared to verify that the proposed phase-phase rectification control strategy can realize the input current of three cells following the respective input voltage under non-sinusoidal asymmetric voltage conditions,thereby achieving unit power factor and improving the utilization ratio of electric energy.Through pre-stage and post-stage main circuits control,the three-phase input currents are equal,and a stable DC voltage is obtained.The feasibility of the designed circuit and the rationality of the control scheme are verified by analyzing the simulated waveform.