Waveform Control Of Repetitive Pulsed Flat-top High Magnetic Field Based On Pulsed Generator System

As the repetitive pulsed flat-top high magnetic field(RPFHMF)has the advantages of repetitive pulsed magnetic field and pulsed flat-top magnetic field,and the RPFHMF system can run for a long time to improve test efficiency,so it meets the needs of various scientific experiments and industrial applications(such as neutron diffraction,magnetic refrigeration,terahertz source,etc.),and it has wide application prospects.When generating the RPFHMF by pulsed magnets,due to the limited capability of heat dissipation,the magnet’s temperature and resistance drastically changes,leading to inconsistencies of the waveform.Therefore,it’s necessary to study the control strategy of RPFHMF waveform to improve waveform quality.The RPFHMF system consists of two parts: power supply and load.The power supply mainly includes the following types: the storage capacitors,the pulse generator-rectifier and the battery.In order to control the magnetic field waveform,the output voltage of the power supply needs to be adjusted to make the magnet current meet the given.The waveform quality of the magnetic field is closely related to the power system and control strategy.In this paper,based on extensive reading of the relevant literature,and combined with the existing power supply type of Wuhan National High Magnetic Field Center(WHMFC),the pulse generator-12 pulse rectifier system is selected as the power supply of the RPFHMF system.And it takes advantage of the good control characteristics of the pulse generator-12 pulse rectifier system to control the magnetic field waveform.The pulse generator-rectifier system is a complicated system.There is mutual influence of the pulse generator,rectifier unit and load,which makes it difficult to analyze the characteristics of the power supply.Aiming at these problems,this paper established a suitable generator and transformer model,which greatly simplifies the analysis of the pulse generator-rectifier system.Based on the fully considering the interaction of various parts in the power system,this paper analyzes its working process by taking the pulse generator-12 pulse rectifier as a whole.As a result,the external characteristic equation of the output voltage is obtained.Due to the drastic changes in the magnet resistance and the power supply has nonlinearity,time delay and time varying characteristics make it difficult to control the magnetic field waveform during the operation of the RPFHMF system.Against the changes of the pulse magnet resistance during the discharge process,this paper proposed a method using the adding window least squares algorithm for online identifying the magnet resistance,and compensate the voltage in the controller to improve the adaptability of the control system.In order to enhance control accuracy,this paper proposes a phase locked loop structure to quickly track the change of the generator angular speed,ensuring the accurate triggering of the rectifier.In order to control the RPFHMF waveform,a generalized model predictivesection PI controller was designed to control the whole waveform and eliminate the influences of nonlinearity and time delay characteristics in the system.Finally,in this paper,the corresponding simulation circuit was built based on the Matlab/Simulink simulation platform.In order to verify the correctness of the pulse generator rectifier system’s model and the effectiveness of controller,the control algorithm for the pulse generator-12 pulse rectifier was implemented to generated 20T/100 ms RPFHMF.