| At present,non-controlled rectifier or phase controlled rectifier is often used in the input side power converter of solid-state welder power supply.The power factor of the system is low,and the harmonic content is high,which easily cause power grid pollution.In order to solve this problem,this thesis studied the current source rectifier(CSR),which was suitable for the front input side of the power supply of solid-state welding machine.Because CSR need to output stable DC voltage when it was used in the power supply of welding machine,the output side of CSR could be equivalent to the case of capacitive load.In this thesis,the application of three-phase CSR in the power supply of solid-state welding machine and the control strategy of CSR with capacitive load are mainly studied.Firstly,the three-phase CSR with capacitive load was theoretically analyzed in terms of power topology,basic working principle,device commutation process and mathematical modeling,which provided a theoretical basis for the realization of three-phase CSR system.The commutation process of CSR was decleared in detail,and the voltage stress of switching devices was briefly described.Based on this,the buffer protection circuit of switching devices was designed in the following chapters,which restrained the over-voltage spike and avoided device damage.Secondly,because the capacitor was added to the DC side of the CSR system with capacitive load,when the load of the system fluctuated,the voltage changes lagging behind the current changes,resulting in system fluctuation and control instability.In view of this characteristic,a feed forward decoupling control method based on capacitive energy storage feedback outer loop was proposed.The inner loop used feedforward decoupling method to control the power factor and current harmonics on the network side,and the outer loop used DC side.The method of capacitive energy storage feedback and load power feedforward was used to realize the stable output control of DC voltage and current.The simulation results showed that the proposed method has good performance of tracking and dynamic response,but with the decrease of load,the DC output voltage became more pulsating and the grid side current harmonic distortion became serious.Thirdly,aiming at the problems of current feed-forward decoupling control method based on capacitive energy storage feedback outer loop,a quasi-PR control method based on DC current feed-forward was proposed.The inner loop used quasi-PR control method to realize high power factor and low harmonic distortion rate of current in two-phase static coordinate system.The outerloop used DC voltage feedback and current feed-forward control method to compensate.The influence of load fluctuation on the system was compensated.The simulation results showed that under the same conditions,the output voltage of the system was more stable,the load adaptability was wider,and the control effect of the system could be guaranteed.Finally,in order to verify the feasibility and validity of the control method,the software and hardware of CSR system with capacitive load were designed.Based on this,an experimental prototype was built.The current feed-forward decoupling control method based on capacitive energy storage feedback outer loop and the quasi-PR control method based on DC current feed-forward were compared experimentally,and the practicability of buffer protection circuit for switching devices was analyzed.The experimental results showed that the quasi-PR control method based on DC current feedforward had the advantages of stronger suppression ability of harmonic current on the network side and higher stability of DC output voltage.It also proved the practicability and effectiveness of switching device buffer circuit. |
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