Research On Control Strategy And Topology Of High Parameter Flat-top Pulse High Magnetic Field Power Supply System

As an extreme experimental environment,pulsed high magnetic field is conducive to reveal unknown scientific phenomena and explore effects of substances,so it is widely applied in frontier science fields such as physics,chemistry and biology.Combining the advantages of both pulsed high magnetic field and steady high magnetic field,flat-top longpulse high-magnetic field has become one of the hot topics in the field of strong magnetic field.With the further advance of scientific exploration process,parameters of existing flattop long-pulse high-magnetic field couldn't meet the increasingly stringent requirements of certain scientific experiments.Therefore,improving the parameters of the flat-top long-pulse high-magnetic field is of great theoretical and experimental value.The power supply system is one of the core components of the flat-top pulsed high magnetic field system.Its main types include the pulse generator-rectifier power supply,capacitor power supply,battery power supply,etc.Important parameters(magnetic field peak intensity,flat-top stability and flat-top duration)used in the evaluation of the flat-top magnetic field are closely related to the choice of power supply scheme and the design of control strategy.Therefore,after extensive reading of relevant literature,the key theory and technology of flat pulsed magnetic field power supply system are further researched in this paper based on existing pulse power supply system of Wuhan national high magnetic field center in order to achieve high parameters of flat-top pulse strong magnetic field.The research contents include: the control strategy and dynamic reactive power compensation of 100 MVar pulse generator-rectifier power supply for flat-top magnetic field system,the reactive power compensation system of pulse generator rectifier for flat-top magnetic field system,the active embedded control system for flat-top magnetic field system and multi power combined supply method for flat-top magnetic field system.In research on the control strategy of pulse generator-rectifier power supply,from the aspect of improving control accuracy of time-varying nonlinear complex system,a hardware circuit decoupling scheme and two high-precision control strategies are proposed to improve the flat-top stability of flat-top magnetic field.Aiming to overcome the control difficulty caused by the current coupling effect within 50 T dual-coil magnet,a decoupling transformer whose mutual inductance can counteract with the 50 T magnet's mutual inductance is connected series in the circuit.Implementation accuracy and robustness of the control strategy are improved by hardware circuit decoupling.A compound control strategy based on genetic algorithm(GA)and back propagation(BP)neural network is proposed.GA is used to optimize the initial parameters used in BP neural network,avoiding BP neural network's difficulty of setting initial parameters,problem of easy to fall into local optimum and slow convergence speed.Considering that single closed-loop PI feedback control,feed forward control and double closed ring PI self-tuning control are not adaptable in complex nonlinear time-varying system,the model predictive control strategy(MPC)is proposed in this paper based on the establishment of an external characteristic prediction model of 12 pulse wave rectifier and a nonlinear prediction model of magnetic resistance.A high precision control strategy based on model predictive control of 12 pulse rectifier power supply for flat top magnetic field system is put forward.The digital simulation model based on the pulse generator-rectifier flat-top magnetic field system verifies the effectiveness of the decoupling scheme of the hardware circuit and the control strategy.In research on dynamic reactive power compensation system for the pulse generatorrectifier power supply,from the aspect of reducing the influence of rectifier input voltage fluctuation on control strategy accuracy,a reactive power compensation system is proposed on the basis of 10 MVar STATCOM and 15 MVar single-tuned filter.By reducing the falling amplitude of the input voltage of the rectifier,the problem of decreasing control accuracy with the deepening of discharge time is solved,and it prolongs the flat-top duration of the magnetic field.On the basis of analyzing the variation law of load reactive power,the optimization design is carried out for the reactive power compensation capacity of single tuned filter bank and STATCOM to ensure that the reactive power compensation system has high economy,stability and adaptability.A single tuned filter bank based on thyristor switching shunt capacitor and a STATCOM circuit topology using phase shift transformer for obtaining four reset structure are proposed to compensate the reactive power of the fixed value and also give consideration to the filtering function of the specific subharmonic.A control strategy based on the model prediction method is proposed to accurately track the change of load's reactive power consumption;Based on the simulation model of the pulse generator-rectifier flat-top magnetic field system,reactive power compensation system is established.Combined with the control strategy of pulse generator-rectifier power supply for flat-top magnetic field system which is based on the model predictive control(MPC),the operation status of the reactive power compensation system is analyzed and the compensation effect is verified.In research on the active embedded control system for flat-top magnetic field,from the perspective of tracking and compensating the magnetic field fluctuation in the flat-top stage,an active embedded magnetic field control system based on magnetic field superposition principle is proposed to improve the stability of flat-top magnetic field.A full bridge MOSFET circuit based on supercapacitor is proposed to achieve two-way flow of energy and generate compensation magnetic field for tracking magnetic field fluctuations;The control system magnet coil that can be embedded in the original magnet is designed under the considerations of scientific experiment requirements,engineering realization and generality;It's proposed to series connect the smoothing inductor in the discharge circuit to avoid the overcompensation caused by excessive voltage of mutual inductance;A control strategy on the basis of bipolar PWM is proposed to meet the requirements of the compensation system for response speed,compensation precision and robustness.And the coordinated control strategy of pulse generator-rectifier power supply system and the active magnetic field control system is further proposed;On the digital simulation platform which is combined respectively with the flat-top magnetic field system powered by capacitor,battery and pulse generator-rectifier,the working process of the active magnetic field control system is analyzed,and effectiveness of the control system is verified.In research on multi power combined power supply system,from the aspect of combining various advantages of different power supply system,a variety of combined power supply system is put forward to improve the peak field strength while maintaining the duration and stability of the flat-top.Circuit topology and magnet parameters of various combined power supply systems are designed.The evaluation function reflecting economy and engineering realization of magnet coil for combined power supply system is proposed;The combined power supply system consisting of a capacitor parallel to the pulse generatorrectifier power supply obtains the highest peak value of magnetic field,and its economic and engineering realization of magnet coil is the best,thus both the circuit topology and the 65 T dual-coil magnet based on this combined power supply system are further optimized;Aiming to solve the problem of the short circuit breakdown which may appear once the output voltage difference between the two kinds of power supply is large,the protection system of multi power supply cooperative work is proposed for the 65 T flat-top magnetic field system;A coordinated control strategy of multi power supply for 65 T flat-top magnetic field system is proposed to achieve high precision control of coil current;A simulation model of 65 T flattop magnetic field system is established on the digital simulation platform,and the effectiveness of the system is verified.