Study On The Power Supply To Realize The High-Stability Flat-Top Of The Long-Pulse Magnetic Field

There are separate characteristics while only using traditional continuous magnetic field or traditional pulsed magnetic field. Continuous magnetic field is featured by its low ripple and long duration. But there are several drawbacks, such as the field lower than 50 T and the high cost. Pulsed magnetic field is featured by its high field and low cost. But the duration is always short and the field changes with time. Considering aspects of the field and the stability, the long-pulse magnetic field with high-stability flat-top, can combine the advantages of the two fields above. So that it can meet the requirements of these extreme experiments, such as material specific heat test and nuclear magnetic resonance. Therefore, it is important to realize the high-stability flat-top of the long-pulse magnetic field.The power supply system is one of the core elements to realize the high magnetic fields. There are many types of the power supply systems, such as pulse capacitors, storage coils, pulse generators, rectifiers powered by the grid and etc. The design of the power supply, the selection of parameters, and the control strategy implementation, directly determine the quality of the magnetic field waveform, whereas scientific experiments related may be impacted. Therefore, the design and implementation of the power supply to realize the high-stability flat-top of the long-pulse magnetic field, will be the main contents of this thesis.The pulse generator is composed of an induction motor and a synchronous generator. The equivalent model of the induction motor is established oriented by the stator flux. To accelerate the speed of the motor-generator, a double-loop decoupling control strategy for the converter at the rotor side is proposed. Thus, the energy stored can be released in full. To guarantee the operation of the phase-controlled rectifier, the effect of the AC side impedance is analyzed. A RC filter solution is proposed to deal with the oscillation which might be caused by the AC side cable. Based on the analyses of the input and output characteristics of the phase-controlled rectifier, a solution to switch a group of single-tuned filters on different time is adopted. Therefore, the AC side power quality may be improved without reactive-power reversing.To suppress the high-frequency oscillations caused by the stray capacitance of the coaxial cable, a paralleled RC filter branch is adopted. In order to attenuate the even ripple in the DC side brought by the phase-controlled rectifier, a combined passive filter scheme is proposed. Meanwhile, the oscillations can be also eliminated. To better the performance, a DC-side shunt active power filter scheme, is proposed to attenuate the DC current ripple in an effective way. The detection method and the control strategy are detailed. Simulation results verify the feasibility of the active filtering scheme.Two single-coil quasi-continuous magnets are designed with the efficient design software respectively. Taking account of the resistance rise of the coils, the repetitive control is utilized in the composite control strategy which is composed of the firing angle open-loop and the magnet current (or magnetic field) closed-loop. The tracking error can be minimized, whereas the high-stability flat-top of the long-pulse magnetic field could be realized. Based on the research above, a novel topology of the power supply is proposed, which combines the battery bank and the phase-controlled rectifier in series. The novel topology can provide a wider flat-top than the normal topology.Taking account of design factors of the quasi-continuous magnet, a two-coil magnet is designed. The coupling problem is described. One decoupling transformer is utilized to decouple the mutual inductance. Based on this method, several power supply solutions are proposed, such as the supply combination with the phase-controlled rectifier and the pulse capacitor, the supply combination with the phase-controlled rectifier and the battry bank, and the supply combination with two phase-controlled rectifiers. A digital control method is presented without the decoupling transformer. The repetitive control strategy is applied, so that the phase-controlled rectifiers output an extra voltage to offset the mutual inductance effect. Simulation results are presented to validate the effectiveness of the methods proposed, and characteristics of the combination supplies are compared, which can guide the implementation of the project.